Arbiter Systems 931A Operation Manual

Operation Manual 931A POWER SYSTEM ANALYZER CURRENT VOLTAGE TRANSDUCER TIMER SETUP 1 SETUP 2 SETUP 3 SETUP 4 SETUP 5 SETUP 6 NARROW-BAND-WIDE MEAS 3 PHASE CH1 RANGE RESTART CONFIG SHIFT HELP REVIEW PRINT LOG STORE SETUP SCALE ESCAPE ENTER VOLTS AMPS PHASE FREQUENCY POWER VARS VA PF HARMONICS WAVEFORM CHANNEL 1 SELECT CHANNEL 2 SELECT MEASURE HOLD CH2 RANGE MIN MAX TRANSDUCER MENU LOG DATA PRINT LAST SETUP CH1 / CH2 ON/OFF FUSE 1AF/250V 85-264 Vac 47-440 Hz 110-250 Vdc RS-232 GROUND BEFORE USE DISPLAY CONFIG ARM / RESET A B C N 750 Vrms / 1000 Vdc MAX 20 Arms MAX 10Vdc MAX 100mAdc MAX A B 300V MAX A B Arbiter Systems, Inc. Paso Robles, CA 93446 U.S.A. www.arbiter.com

Systems. Reasonable effort was made to verify that all contents were accurate as of the time of publication. Check with Arbiter Systems at the address below for any revisions made since the original date of publication. Contact Information Arbiter Systems, Inc. 1324 Vendels Circle, Suite 121 Paso Robles, CA 93446 (805) 237-3831 www.arbiter.com [email protected] [email protected] Definition This manual describes the Model 931A Power System Analyzer—, and accessories. Firmware and Firmware Updates This manual was created based on the following firmware: Copyright Program: 10 February 2010 Help Version: 25 JUNE 1996 DSP Version: 093098 The firmware versions indicated above are displayed on the Model 931A at startup. To freeze the display during this screen, press and hold the ESCAPE key until finished viewing. Also, the 931A will issue this information from the serial port using the VER command. See the VER command on page 124. Firmware Updates are available as a ROM replacement from Arbiter Systems by contacting technical support at the information above. ii

product manufactured or sold by Arbiter Systems except for the following limited warranty against defects in materials and workmanship on products manufactured by Arbiter Systems. Products manufactured by Arbiter Systems are guaranteed against defective materials and workmanship under normal use and service for one year from the date of delivery. The responsibility of Arbiter Systems under this warranty is limited to repair or replacement, at Arbiter Systems’ option, of any product found to be defective. Arbiter Systems shall have no liability under this warranty unless it receives written notice of any claimed defect, within the earlier of: ˆ Thirty days of discovery by Buyer, or; ˆ One year from the date of delivery. For warranty service or repair, products must be returned to a service facility designated by Arbiter Systems. Buyer shall prepay all shipping charges, duties, and taxes to send the product to Arbiter Systems and Buyer shall prepay shipping charges, duties, and taxes to return the product to Buyer. THE WARRANTY SET FORTH HEREIN CONSTITUTES THE ONLY WARRANTY OBLIGATIONS OF ARBITER SYSTEMS, EX- PRESSED OR IMPLIED, STATUTORY, BY OPERATION OF LAW, OR OTHERWISE. ARBITER SYSTEMS DISCLAIMS ANY WAR- RANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICU- LAR PURPOSE, AND BUYER EXPRESSLY WAIVES ALL OTHER WARRANTIES. This limited warranty does not extend to any product, which has been subject to: 1. Improper use or application, abuse, or operation beyond its rated capacity, or contrary to the instructions in the operation and maintenance manuals (if any); 2. Accident; 3. Repair or maintenance performed by Buyer, except in accordance with the operation and maintenance manuals, if any, and any special instructions of Arbiter Systems; 4. Modification without the prior written authorization of Arbiter Systems (whether by the substitution of non-approved parts or otherwise). iii

In no event shall Arbiter Systems be liable for direct, indirect, incidental or consequential damages (including loss of profits), whether based on contract, tort, or other legal theory. FOR THE FASTEST POSSIBLE SERVICE, PLEASE PROCEED AS FOLLOWS: 1. Notify Arbiter Systems, Inc., specifying the instrument model number and serial number and giving full details of the difficulty. Service data or instrument-return authorization will be provided upon receipt of this information. 2. If instrument return is authorized, forward prepaid to the manufac- turer. If it is determined that the instrument is not covered by this warranty, an estimate will be made before the repair work begins, if requested. See Contact Information on page ii. iv

Model 931A Power System Analyzer Operation Manual Table of Contents Chapter 1 General Information Chapter 2 Functional Description Chapter 3 Operation Chapter 4 Specifications Appendix A RS-232 Commands Appendix B Optional Accessories Appendix C CE Mark Certification Index Copyright Arbiter Systems Incorporated September 2021 All rights re- served. International copyright secured. PD0017400T Reorder Number: AS0094000 v

1 1.2 Supplied Equipment . . . . . . . . . . . . . . . . . . . . . . 1 1.3 Available Accessories . . . . . . . . . . . . . . . . . . . . . . 2 2 Functional Description 3 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2 Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2.1 Voltage . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2.2 Current . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2.3 Transducer . . . . . . . . . . . . . . . . . . . . . . . 5 2.2.4 Timer . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.3 Measurement Channels . . . . . . . . . . . . . . . . . . . . . 5 2.4 Measurement Method . . . . . . . . . . . . . . . . . . . . . 6 2.4.1 Sampling and Filtering . . . . . . . . . . . . . . . . . 8 2.5 User Interface . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.5.1 Graphics Display . . . . . . . . . . . . . . . . . . . . 8 2.5.2 Keypad . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.6 RS-232C Interface . . . . . . . . . . . . . . . . . . . . . . . 9 2.7 Power Supply and Battery . . . . . . . . . . . . . . . . . . . 9 2.7.1 Battery Power . . . . . . . . . . . . . . . . . . . . . 9 2.7.2 Line Power/Battery Charging . . . . . . . . . . . . . 10 2.7.3 Auto-Shutdown Mode . . . . . . . . . . . . . . . . . 11 2.8 Start-Up Sequence . . . . . . . . . . . . . . . . . . . . . . . 11 2.8.1 Holding the Start-Up Sequence . . . . . . . . . . . . 11 2.8.2 Reset – Instrument Default Setup . . . . . . . . . . 11 3 Operation 13 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 3.2 Front Panel Connections . . . . . . . . . . . . . . . . . . . . 13 vii

13 3.2.2 Voltage Inputs . . . . . . . . . . . . . . . . . . . . . 14 3.2.3 Current Inputs . . . . . . . . . . . . . . . . . . . . . 14 3.2.4 Transducer Inputs . . . . . . . . . . . . . . . . . . . 15 3.2.5 Timer Inputs . . . . . . . . . . . . . . . . . . . . . . 15 3.3 Front Panel Keys . . . . . . . . . . . . . . . . . . . . . . . . 15 3.3.1 Main Functions . . . . . . . . . . . . . . . . . . . . . 15 3.3.2 Secondary Functions . . . . . . . . . . . . . . . . . . 26 3.3.3 Data Entry Functions . . . . . . . . . . . . . . . . . 41 3.3.4 Timer Control Functions . . . . . . . . . . . . . . . . 42 3.4 Front Panel Display . . . . . . . . . . . . . . . . . . . . . . 44 3.5 Direct Measurements . . . . . . . . . . . . . . . . . . . . . . 44 3.5.1 AC Voltage Measurement . . . . . . . . . . . . . . . 44 3.5.2 AC Current Measurement . . . . . . . . . . . . . . . 46 3.5.3 DC Voltage Measurement . . . . . . . . . . . . . . . 48 3.5.4 Frequency Measurement . . . . . . . . . . . . . . . . 49 3.5.5 Harmonic Measurement . . . . . . . . . . . . . . . . 50 3.6 Combined Measurements . . . . . . . . . . . . . . . . . . . 52 3.6.1 Phase Angle Measurement . . . . . . . . . . . . . . . 52 3.6.2 Active Power – Reactive Power . . . . . . . . . . . . 54 3.6.3 Apparent Power – Power Factor . . . . . . . . . . . 56 3.6.4 Waveform Display . . . . . . . . . . . . . . . . . . . 58 3.7 Timer Measurements . . . . . . . . . . . . . . . . . . . . . . 58 3.7.1 Connecting the Inputs . . . . . . . . . . . . . . . . . 59 3.7.2 Configuring the Timer . . . . . . . . . . . . . . . . . 59 3.7.3 Timer Measurement Categories . . . . . . . . . . . . 62 3.8 Transducer Testing . . . . . . . . . . . . . . . . . . . . . . . 64 3.8.1 Configuring the Transducer . . . . . . . . . . . . . . 64 3.8.2 Connecting the Inputs . . . . . . . . . . . . . . . . . 70 3.8.3 Connecting the Outputs . . . . . . . . . . . . . . . . 75 3.8.4 Performing the Measurement . . . . . . . . . . . . . 75 3.8.5 Custom Pulse, or Contact Output Tests . . . . . . . 75 3.8.6 Performing a Test . . . . . . . . . . . . . . . . . . . 80 3.9 Using External PT’s and CT’s . . . . . . . . . . . . . . . . 84 3.10 Data Logging . . . . . . . . . . . . . . . . . . . . . . . . . . 84 3.10.1 Capturing Data . . . . . . . . . . . . . . . . . . . . . 84 3.10.2 Reviewing Data . . . . . . . . . . . . . . . . . . . . . 85 3.10.3 Erasing Logged Data . . . . . . . . . . . . . . . . . . 86 3.11 Printing / Exporting Data . . . . . . . . . . . . . . . . . . . 86 3.11.1 Print / Data Export Setup . . . . . . . . . . . . . . 86 3.11.2 ASCII Format . . . . . . . . . . . . . . . . . . . . . 87 3.11.3 Graphics Format (FX-80) . . . . . . . . . . . . . . . 87 viii

87 3.11.5 Spreadsheet . . . . . . . . . . . . . . . . . . . . . . . 88 3.11.6 Initiating Printing / Exporting . . . . . . . . . . . . 97 4 Specifications 99 4.1 Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 4.1.1 Voltage . . . . . . . . . . . . . . . . . . . . . . . . . 99 4.1.2 Current . . . . . . . . . . . . . . . . . . . . . . . . . 99 4.1.3 Transducer . . . . . . . . . . . . . . . . . . . . . . . 99 4.1.4 Timer . . . . . . . . . . . . . . . . . . . . . . . . . . 100 4.2 Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . 100 4.2.1 Voltage and Current . . . . . . . . . . . . . . . . . . 100 4.2.2 Phase Angle . . . . . . . . . . . . . . . . . . . . . . . 100 4.2.3 Frequency . . . . . . . . . . . . . . . . . . . . . . . . 101 4.2.4 Timer . . . . . . . . . . . . . . . . . . . . . . . . . . 101 4.2.5 Transducer . . . . . . . . . . . . . . . . . . . . . . . 101 4.2.6 Harmonics . . . . . . . . . . . . . . . . . . . . . . . . 101 4.2.7 Power Quantities . . . . . . . . . . . . . . . . . . . . 101 4.3 General Specifications . . . . . . . . . . . . . . . . . . . . . 102 4.3.1 Measurement Bandwidth . . . . . . . . . . . . . . . 102 4.3.2 Memory . . . . . . . . . . . . . . . . . . . . . . . . . 102 4.3.3 Display . . . . . . . . . . . . . . . . . . . . . . . . . 102 4.3.4 Keypad . . . . . . . . . . . . . . . . . . . . . . . . . 102 4.3.5 Environment . . . . . . . . . . . . . . . . . . . . . . 102 4.3.6 Input Power . . . . . . . . . . . . . . . . . . . . . . . 103 4.3.7 Serial Port . . . . . . . . . . . . . . . . . . . . . . . 103 A RS-232C Commands 105 A.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 A.2 Serial Port Examples . . . . . . . . . . . . . . . . . . . . . . 106 A.3 Command Summary . . . . . . . . . . . . . . . . . . . . . . 107 A.3.1 Battery Charging Status (BAT) . . . . . . . . . . . 107 A.3.2 Backlight Set (BLT) . . . . . . . . . . . . . . . . . . 107 A.3.3 Channel Calibrate (CCH) . . . . . . . . . . . . . . . 107 A.3.4 Ratio CH1/CH2 (CCR) . . . . . . . . . . . . . . . . 108 A.3.5 Channel Input Select (CHS) . . . . . . . . . . . . . . 108 A.3.6 Calibrate Input (CIN) . . . . . . . . . . . . . . . . . 109 A.3.7 Transducer Configuration (COT) . . . . . . . . . . . 109 A.3.8 Daylight Saving Time, Set (DAY) . . . . . . . . . . 110 A.3.9 Display Dump, ASCII (DDA) . . . . . . . . . . . . . 110 A.3.10 Data Dump, Bitmapped (DDB) . . . . . . . . . . . 111 A.3.11 Store Calibration Data in EEPROM (EEP) . . . . . 111 ix

A.3.13 Frequency, Return (FRQ) . . . . . . . . . . . . . . . 111 A.3.14 Timer Calibrate (FTM) . . . . . . . . . . . . . . . . 112 A.3.15 Harmonics Display (HAR) . . . . . . . . . . . . . . . 112 A.3.16 Harmonic Magnitude, Return (HMA) . . . . . . . . 112 A.3.17 Harmonic Phase Angle, Return (HPH) . . . . . . . . 113 A.3.18 Power Down (KIL) . . . . . . . . . . . . . . . . . . . 113 A.3.19 Log Data (LOG) . . . . . . . . . . . . . . . . . . . . 113 A.3.20 Last Setup (LSU) . . . . . . . . . . . . . . . . . . . 113 A.3.21 Magnitude (Channel), Return (MAG) . . . . . . . . 114 A.3.22 Measure Hold (MHD) . . . . . . . . . . . . . . . . . 114 A.3.23 MIN/MAX, Display (MMN) . . . . . . . . . . . . . 114 A.3.24 Bandwidth-Narrow, Set (NAB) . . . . . . . . . . . . 114 A.3.25 Overload Status (OVD) . . . . . . . . . . . . . . . . 115 A.3.26 Phase/Frequency Display (P F) . . . . . . . . . . . . 115 A.3.27 Power/Vars Display (P V) . . . . . . . . . . . . . . . 115 A.3.28 Power Factor, Return (PFA) . . . . . . . . . . . . . 115 A.3.29 Phase Mode, Set (PHM) . . . . . . . . . . . . . . . . 116 A.3.30 Phase, Return (PHS) . . . . . . . . . . . . . . . . . 116 A.3.31 Power, Return (PWR) . . . . . . . . . . . . . . . . . 116 A.3.32 Range Hold, Set (RHD) . . . . . . . . . . . . . . . . 117 A.3.33 Logged Data, Review (RLD) . . . . . . . . . . . . . 117 A.3.34 Range Hold, Release (RRH) . . . . . . . . . . . . . . 117 A.3.35 MIN/MAX, Restart (RST) . . . . . . . . . . . . . . 117 A.3.36 Transducer Channel (SCC) . . . . . . . . . . . . . . 118 A.3.37 Serial Number (SER) . . . . . . . . . . . . . . . . . 118 A.3.38 Flash Log (SLO) . . . . . . . . . . . . . . . . . . . . 118 A.3.39 Scale On/Off (SOO) . . . . . . . . . . . . . . . . . . 119 A.3.40 DSP Speed (SPD) . . . . . . . . . . . . . . . . . . . 119 A.3.41 Phase Preference, Set (SPH) . . . . . . . . . . . . . 119 A.3.42 Range, Set (SRG) . . . . . . . . . . . . . . . . . . . 120 A.3.43 Scale Factors, Set or Return (SSC) . . . . . . . . . . 120 A.3.44 Store Setup (SST) . . . . . . . . . . . . . . . . . . . 121 A.3.45 Setup, Recall (SUP) . . . . . . . . . . . . . . . . . . 121 A.3.46 Timer, Arm (TAM) . . . . . . . . . . . . . . . . . . 121 A.3.47 Time, Return (TDR) . . . . . . . . . . . . . . . . . . 121 A.3.48 Time, Set (TDS) . . . . . . . . . . . . . . . . . . . . 121 A.3.49 Timer Configuration, Set or Return (TCF) . . . . . 122 A.3.50 Transducer Display (TDU) . . . . . . . . . . . . . . 122 A.3.51 Timer Display (TIM) . . . . . . . . . . . . . . . . . 123 A.3.52 Timer Reading, Return (TMR) . . . . . . . . . . . . 123 A.3.53 Timer, Reset (TRS) . . . . . . . . . . . . . . . . . . 123 x

A.3.55 Timer, Start (TST) . . . . . . . . . . . . . . . . . . 123 A.3.56 Volts/Amps Display (V A) . . . . . . . . . . . . . . 123 A.3.57 VA/PF Display (V P) . . . . . . . . . . . . . . . . . 124 A.3.58 Volt-Amps, Return (VAM) . . . . . . . . . . . . . . 124 A.3.59 VARS, Return (VAR) . . . . . . . . . . . . . . . . . 124 A.3.60 Version, Return (VER) . . . . . . . . . . . . . . . . 124 A.3.61 Waveform Display (WAV) . . . . . . . . . . . . . . . 125 A.3.62 Bandwidth Wide, Set (WIB) . . . . . . . . . . . . . 125 A.3.63 Transducer Input, Display (XDI) . . . . . . . . . . . 125 A.3.64 Transducer Output, Display (XDO) . . . . . . . . . 125 B Optional Accessories 127 B.1 Precision Current Transformer . . . . . . . . . . . . . . . . 127 B.1.1 Specifications . . . . . . . . . . . . . . . . . . . . . . 127 B.1.2 Input Connections . . . . . . . . . . . . . . . . . . . 127 B.1.3 Current Display . . . . . . . . . . . . . . . . . . . . 128 B.2 Handle/Bail . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 B.2.1 Parts and Accessories . . . . . . . . . . . . . . . . . 128 B.2.2 Required Tools . . . . . . . . . . . . . . . . . . . . . 128 B.2.3 Procedure . . . . . . . . . . . . . . . . . . . . . . . . 128 B.2.4 Operation . . . . . . . . . . . . . . . . . . . . . . . . 128 B.3 Extended Memory . . . . . . . . . . . . . . . . . . . . . . . 129 B.3.1 Data Organization . . . . . . . . . . . . . . . . . . . 130 B.3.2 Computing the Number of Files and Records . . . . 132 B.3.3 Log Data Triggering . . . . . . . . . . . . . . . . . . 133 B.3.4 Front Panel Operation . . . . . . . . . . . . . . . . . 134 B.3.5 Remote Operation . . . . . . . . . . . . . . . . . . . 135 B.3.6 Setup of Logged Data Operation . . . . . . . . . . . 135 B.3.7 Review of Logged Data . . . . . . . . . . . . . . . . 137 B.3.8 Trigger Remote Data Logging . . . . . . . . . . . . . 138 C CE Mark Certification 139 xi

2.1 Model 931A Front Panel . . . . . . . . . . . . . . . . . . . . 4 2.2 Input Multiplexing . . . . . . . . . . . . . . . . . . . . . . . 5 3.1 Phase, Power Factor, and VAR Definitions . . . . . . . . . . 19 3.2 Phase, Power Factor, VAR Quadrants . . . . . . . . . . . . 20 3.3 Three-Phase Measurement Selection . . . . . . . . . . . . . 28 3.4 Three Phase Display Selection . . . . . . . . . . . . . . . . . 28 3.5 Three Phase Tabular Display . . . . . . . . . . . . . . . . . 28 3.6 Three-Phase Displays for an ABC System . . . . . . . . . . 32 3.7 Three-Phase Displays for a CBA System . . . . . . . . . . . 33 3.8 1-Phase, 2-Wire, 1-Element Connections . . . . . . . . . . . 34 3.9 1-Phase, 3-Wire, 2-Element Connections . . . . . . . . . . . 34 3.10 3-Phase, 3-Wire, 2-Element Connections . . . . . . . . . . . 35 3.11 3-Phase, 4-Wire, 2.5-Element Connections . . . . . . . . . . 35 3.12 3-Phase, 4-Wire, 3-Element Connections . . . . . . . . . . . 36 3.13 Phase Angle Example . . . . . . . . . . . . . . . . . . . . . 54 3.14 1-Phase, 2-Wire, 1-Element Transducer Test . . . . . . . . . 71 3.15 1-Phase, 3-Wire, 2-Element Transducer Test . . . . . . . . . 72 3.16 3-Phase, 4-Wire, 2.5-Element Transducer Test . . . . . . . . 73 3.17 3-Phase, 4-Wire, 3-Element Transducer Test . . . . . . . . . 74 3.18 3-Phase, 4-Wire, 3-Element Custom Pulse Transducer Test 83 B.1 Model 931A Case with Handle/Bail . . . . . . . . . . . . . 129 xiii

2.1 AC Measurement Configurations . . . . . . . . . . . . . . . 6 2.2 DC Measurement Configurations . . . . . . . . . . . . . . . 7 2.3 RS-232C Port Pinout / Signal Description . . . . . . . . . . 10 2.4 931A Reset Selection Screen . . . . . . . . . . . . . . . . . . 12 3.1 Phase Angle Preferences . . . . . . . . . . . . . . . . . . . . 20 3.2 Channel 2, AC Voltage Ranges, Vrms . . . . . . . . . . . . 23 3.3 Channel 2, AC Current Ranges, Arms . . . . . . . . . . . . 23 3.4 Channel 2, DC Voltage Ranges, Vdc . . . . . . . . . . . . . 23 3.5 Channel 1, AC Voltage Ranges, Vrms . . . . . . . . . . . . 37 3.6 Channel 1, AC Current Ranges, Arms . . . . . . . . . . . . 37 3.7 Channel 1, DC Voltage Ranges, Vdc . . . . . . . . . . . . . 37 3.8 Phase Convention . . . . . . . . . . . . . . . . . . . . . . . . 54 B.1 Custom Data Table . . . . . . . . . . . . . . . . . . . . . . . 132 xv

art instrument offering unprecedented accuracy in the measurement of pa- rameters related to AC Power Generation, Transmission, and Distribution. Using Arbiter’s proprietary PowerDSA— Digital Signal Processing (DSP) circuitry, the Model 931A greatly enhances the precision measurement of these AC parameters. Powered by either an internal rechargeable battery or by AC line voltage, the Model 931A is truly portable. This manual is divided into four chapters and two appendices as follows: Chapter 1. General Information Chapter 2. Functional Description Chapter 3. Operation Chapter 4. Specifications Appendix A. RS-232C Commands Appendix B. Optional Accessories 1.2 Supplied Equipment The Model 931A is supplied with a standard AC Power Cord (P09R), RS- 232 Null-Modem Cable (P/N CA0019806), Safety Ground Lead (812HA-8) and one Operations Manual (AS0094000). 1

Model Number Description 931A/01 16-Megabyte internal memory AS0060000 PowerCSV, Applications software (download only). Requires Option 01 AS0035901 Adjustable handle/bail Assembly 09311A 400 Amp 20:1 precision CT, 0.1% accuracy. Includes AS0036000 Mounting Bracket AP0012800 1000:1 Clamp-on CT, 200 Amps AP0012900 250:5, 500:5, 1000:5 Clamp-on CT, 1000 Amps AP0001300 1000:1; 1000A, 600V, Cat. III, EN61010 811AT/CT* 3-Phase Universal Test Plug Current Lead Set 813AT/BT* 3-Phase Safety Voltage Lead Set 815AT/BT* 3-Phase Fused Voltage Lead Set 816AT/CT* 3-Phase Spade-lug Current Lead Set 817AT* 3-Phase CT Lead Set: red, yellow, blue * This is a partial list. Other high-quality test leads and accessories are also available. Contact Arbiter Systems for further information. 2

Model 931A components. Figure 2.1 illustrates the front panel. 2.2 Inputs 2.2.1 Voltage Measure AC or DC voltages through four color-coded insulated banana jacks on the front panel. Labeled A, B, C, and N, each terminal can accept input voltages of up to 750 Vrms or 1000 Vdc. Each input voltage terminal is isolated from signal common with an impedance of 1 megohm, and is physically isolated from the chassis. 2.2.2 Current The 931A features three independent, transformer-coupled AC current inputs, accessible via three pairs of front-panel binding posts, which are color-coded for polarity and labeled A, B, and C. Each terminal can accept an AC signal with a rms current value of up to 20 amps. All current inputs are isolated to withstand a potential of 1000 Vpeak from chassis ground. 3

CURRENT VOLTAGE TRANSDUCER TIMER SETUP 1 SETUP 2 SETUP 3 SETUP 4 SETUP 5 SETUP 6 NARROW-BAND-WIDE MEAS 3 PHASE CH1 RANGE RESTART CONFIG SHIFT HELP REVIEW PRINT LOG STORE SETUP SCALE ESCAPE ENTER VOLTS AMPS PHASE FREQUENCY POWER VARS VA PF HARMONICS WAVEFORM CHANNEL 1 SELECT CHANNEL 2 SELECT MEASURE HOLD CH2 RANGE MIN MAX TRANSDUCER MENU LOG DATA PRINT LAST SETUP CH1 / CH2 ON/OFF FUSE 1AF/250V 85-264 Vac 47-440 Hz 110-250 Vdc RS-232 GROUND BEFORE USE DISPLAY CONFIG ARM / RESET A B C N 750 Vrms / 1000 Vdc MAX 20 Arms MAX 10Vdc MAX 100mAdc MAX A B 300V MAX A B Figure 2.1: Model 931A Front Panel 4

These inputs share a common return, and accept signals of up to 10 volts DC, or 100 mA DC. The Model 931A can be configured to measure the voltage or current directly, or convert the signals for display of either measured input units or a percentage of full-scale or percent error. 2.2.4 Timer Timer inputs “A” and “B” accept signals of up to 300 volts peak or DC, without regard to polarity. The timer circuitry can be triggered by application or removal of AC/DC voltage, or by contact closure/opening. Display results of timer measurements in either seconds, or cycles. 2.3 Measurement Channels The Model 931A incorporates two measurement channels, referred to as Channel 1 and Channel 2. Multiplexing of the voltage and current inputs makes it possible to connect them to one or both of these measurement channels, in different configurations. Figure 2.2 illustrates multiplexing of voltage and current inputs between the two measurement channels. Figure 2.2: Input Multiplexing Tables 2.1 and 2.2 list the possible input configurations for the two measurement channels. Table 2.1 lists AC Measurement Configurations and Table 2.2 lists DC Measurement Configurations. Using the two measurement channels individually allows concurrent measurements of separate signals (voltage and/or current). 5

connecting the first voltage (i.e. Va-b) to Channel 1 and the second voltage (i.e. Vc-n) to Channel 2. Likewise, analyze two currents by referencing Channel 2 to Channel 1. For power quantities such as real power (POWER), vars (VARS), Volt-amperes (VA), and power factor (PF), connect the voltage to Channel 1 and current to Channel 2. Since channel 1 is used as the internal reference, connect the lowest distortion input signal to Channel 1. For most power systems the voltage has lower distortion than the current. If analyzing only one signal, it must be connected to Channel 1. If analyzing a single highly distorted waveform, connect a reference signal of the same fundamental frequency to Channel 1 and the highly distorted waveform to Channel 2. Configuration Measured Input Referenced To Va-b Voltage A Voltage input B Vb-c Voltage B Voltage input C Vc-a Voltage C Voltage input A Va-c Voltage A Voltage input C Vc-b Voltage C Voltage input B Vb-a Voltage B Voltage input A Va-n Voltage A Voltage input N Vb-n Voltage B Voltage input N Vc-n Voltage C Voltage input N Va-s Voltage A Synthesized neutral Vb-s Voltage B Synthesized neutral Vc-s Voltage C Synthesized neutral Ia Current A Independent Ib Current B Independent Ic Current C Independent In - (Ia+Ib+Ic) Channel 2 only Table 2.1: AC Measurement Configurations 2.4 Measurement Method The fundamental frequency, of an input signal, is first analyzed by the Model 931A digital signal processing (DSP) algorithms. Using only Channel 1, these measurements require a fairly ”clean” signal. To make accurate measurement of the fundamental frequency, input signal must have less than 30% total harmonic distortion (THD). A stable frequency display indicates that the fundamental measurement was successful. 6

Vb-c Voltage B Voltage input C Vc-a Voltage C Voltage input A Va-c Voltage A Voltage input C Vc-b Voltage C Voltage input B Vb-a Voltage B Voltage input A Va-n Voltage A Voltage input N Vb-n Voltage B Voltage input N Vc-n Voltage C Voltage input N Va-s Voltage A Synthesized neutral Vb-s Voltage B Synthesized neutral Vc-s Voltage C Synthesized neutral Table 2.2: DC Measurement Configurations The Model 931A has two simultaneous measurement modes: wide-band and narrow-band. Except for harmonics and waveform, all measurements are made continuously, regardless of the measurement displayed. Changing the display selection, other than for harmonics or waveform, does not affect the measurement process. In contrast, the 931A measures harmonics and waveform on-demand. The Wide-Band Mode simulates the operation of an extremely accurate analog rms detector or analog multiplier. Therefore, measurements made in wide-band include the effect of harmonics within the instrument’s 3.05 kHz bandwidth. The Narrow-Band Mode is a completely different measurement pro- cess. Through proprietary DSP state-estimation algorithms, it accurately estimates the parameters (viz. frequency, magnitude, and phase angle) of the input waveform. This mode rejects the effects of noise, distortion, and DC offsets, measuring the fundamental parameters with great precision. Unlike an FFT, these algorithms are insensitive to the input frequency, and will make accurate measurements for any frequency within the rated range of 20-500 Hz. For measuring a signal with more than 30% THD, or a signal that has any harmonic with greater amplitude than the fundamental component, apply the signal to be measured to CH2 and a clean synchronous signal with the desired fundamental frequency to CH1. The Model 931A will lock on to the CH1 signal and the CH2 signal can be analyzed. 7

The Model 931A normally samples input signals at approximately 62.5 thousand samples per second (kS/s) and employs a 15 kHz, two-pole analog anti-alias filter. The signals are filtered again using a digital low- pass filter to remove signals outside the measurement bandwidth (3.05 kHz). The digital filter provides greater accuracy and repeatability and a better rejection rate than could be accomplished with analog filtering. Measurements performed with this technique are essentially free of the harmful effects of aliasing. 8,192 samples are taken from Channels 1 and 2 during each mea- surement cycle. This process requires approximately 131 milliseconds. Depending on the exact measurements made, approximately three mea- surement cycles are executed per second. Since substantial dead time between measurements occur, the Model 931A is not capable of performing cycle-by-cycle, real-time monitoring. For fundamental signals below approximately 40 Hz, the sampling rate is automatically reduced to 12.5 Ks/s, allowing accurate measurements at frequencies down to 5 Hz. The record length under these conditions is 655 ms. The Model 931A completes a measurement cycle 2 to 3 times per second. The cycle includes collecting data, processing and displaying results. A faster update rate of 4 to 5 times per second is achieved by initiating the “Fast Mode.” Pressing the shift key twice, or issuing the SPD RS-232 command, starts this mode. The speed increase is accomplished by eliminating the computation of harmonic data. If the unit is in the Fast Mode and the harmonics display is selected it will revert back to normal operation. Using the Fast Mode does not degrade the accuracy of the Model 931A. 2.5 User Interface The user interface for the Model 931A is designed to streamline overall operation by making the most commonly used functions easily accessible. The following paragraphs briefly describe the Model 931A user interface. 2.5.1 Graphics Display A supertwist liquid crystal display (LCD) serves as the main display and is capable of displaying both characters and graphics, including the waveforms of the input signals. The display features a backlight that can be enabled for operation in subdued lighting conditions. 8

functions generally relate to the most commonly used features. Access secondary functions by first pressing the SHIFT key and then the sec- ondary function key. When a menu operation requires cursor movement or data entry, the top row of keys functions as such. 2.6 RS-232C Interface The Model 931A includes an RS-232C communications port, which allows remote control and command of the instrument using a PC, modem, or terminal. When connecting the Model 931A to a PC, use the supplied null-modem cable. The RS-232C port may also be used to connect a printer to the instrument. Serial port configuration information for the RS-232C port is described in Section 4.3.7 and RS-232C commands are listed in Appendix B. Refer to Section 3.11.6 for information on printing and exporting data. Table 2.3 lists the connector types, pin locations and signal descriptions for the RS-232C port of the Model 931A and other devices. Once properly set up, a host computer may assume total control. All functions and data available from the front panel are also available to the host computer. All commands consist of three letter commands preceded in some cases by setup parameters separated by commas. The Model 931A does not echo commands. Once a valid three-letter command has been received, it will be acted upon immediately. The action taken depends on the command given. “Display change,” “setup modification,” “data output (or export),” and “data logging” are some examples. When the Model 931A returns a “?” it signifies an unrecognizable command or an out-of-bounds number. 2.7 Power Supply and Battery The Model 931A can operate either from an internal, rechargeable battery, or from an external AC/DC power source. 2.7.1 Battery Power In normal operation, the battery will operate the Model 931A for eight hours on a full charge. Factors affecting the operating time include: 9

use of the timer and transducer inputs, and the measurement function. 931A PC PC Seiko ATENS EPSON Seiko DPU-411 XP-320 FX-80 DPU-414 DB9F DB9F DB25M DB25M DB25M DB25M DB9M 2 / RXD 3 / TXD 2 / TXD N/C 3 / TXD 2 / TXD 2 / TXD 3 / TXD 2 / RXD 3 / RXD 2 / RXD 2 / RXD 3 / RXD 3 / RXD 4 / DTR N/C N/C N/C N/C N/C N/C 5 / GND 5 / GND 7 / GND 7 / GND 7 / GND 7 / GND 5 / GND 7 / RTS 6 / DSR 5 / CTS N/C 4 / CTS 4 / CTS N/C N/C 8 / CTS 6 / DSR N/C 20 / DSR 20 / DSR N/C 8 / CTS 7 / RTS 4 / RTS 5 / Busy 5 / RTS 5 / RTS 8 / RTS Table 2.3: RS-232C Port Pinout / Signal Description 2.7.2 Line Power/Battery Charging Battery charging occurs whenever power is applied to the Model 931A main power inlet. The internal charger supplies a steady level of power to the instrument, whether powered on or off. If the 931A is powered on, power is split between instrument operation and battery charging. If using the back light, additional power is directed to the instrument, and increases the time to charge the NiMH battery. To charge the battery completely from a depleted state should take approximately 8 hours with the Model 931A powered off. Charge only if ambient temperature is in the range: 0 ◦C – 40 ◦C (32 ◦F – 104 ◦F). NiMH battery charging in the Model 931A is monitored and controlled using three factors: (1) ∆T/∆t, (2) ∆V/∆t, and (3) time. ∆T/∆t: When the cell reaches full charge, most of the charging energy is converted to heat. This increases the rate of change of battery temperature, which can be detected by a sensor such as a thermistor. ∆V/∆t: When the battery is fully charged the voltage across its terminals drops slightly. The charger can detect this and stop charging. Elapsed Time: Total charge time is monitored and battery charging stops when the preprogrammed time interval has elapsed. The low battery state is indicated on the main display by “LOW BAT!!”, and flashes On and Off. The Model 931A will automatically shut down if the low battery condition persists for longer than several minutes. It is recommended that the unit be charged or shut off when it indicates a low battery condition. 10

ment power if no input signals are present and no keystrokes occur within a period of approximately 10 minutes. To return to normal operation, simply press the ON/OFF key. Activate the Auto-Shutdown Mode by using the MENU key (see Section 3.3.1.13). 2.8 Start-Up Sequence Several tasks are performed during the power-on initialization sequence. First, the Model 931A reads calibration data from the EEPROM (installed only in units with serial numbers greater than A0194). The initial sign-on message reports any errors in the calibration data along with the cali- bration date. These errors are corrected using a built-in Hamming Code Algorithm. If the number of reported errors increases with subsequent start-ups it is an indication that the EEPROM should be replaced. The calibration date is displayed as a decimal number with the format: MMDDYY. The second part of the sign-on display shows the ROM program copyright date, the Help ROM version date and the DSP ROM version date. The DSP ROM date is displayed as a decimal number in the format: MMDDYY. As new features are added to the Model 931A these dates are updated. 2.8.1 Holding the Start-Up Sequence Holding the escape key during the startup sequence holds the startup displays, including the two parts mentioned above. Holding the enter key during the startup sequence allows resetting the setup parameters of calibration. 2.8.2 Reset – Instrument Default Setup To reset the instrument to original default conditions when it shipped from the factory, follow the resetting procedure listed below. Three menu selections are available, shown in the simulated display below. Normally, only the first or second items should be selected. Selecting FULL will completely reset the instrument and calibration constants will be lost. To reset the 931 to factory defaults, select PARTIAL. To escape from this menu, select EXIT and press the ENTER key. 11

EXIT (Nothing Disturbed) PARTIAL (Calibration Not Disturbed) FULL (All Values Set To Default) Table 2.4: 931A Reset Selection Screen 2.8.2.1 Resetting Procedure NOTE: DO NOT SELECT “FULL” UNLESS YOU INTEND TO COMPLETELY ERASE THE INSTRUMENT CALIBRATION! NOTE: Normally, select “PARTIAL” to restore the instrument to original default conditions. 1. Press the ON/OFF button to start the unit. 2. Press and release the ENTER key when the first display screen becomes visible. 3. Using the Cursor keys (up or down arrows) select “PARTIAL” from the three options shown in Table 2.4. 4. Press ENTER and the instrument should ask, “ARE YOU SURE?? YES=UP NO=DOWN”. Press the UP arrow to complete the reset procedure. Otherwise, press the DOWN arrow to escape. 5. The display should indicate the message, “PLEASE WAIT 10s TO 4m”. After a short time the display should return to the final VOLTS AMPS display indication. 6. You may need to configure your settings under MENU and/or SHIFT > SCALE. 12

Analyzer. Topics discussed in this section include: Front panel connectors, front panel controls and display, measurement configuration, taking mea- surements, use of external PT’s and CT’s, data logging, and printing/data exporting. 3.2 Front Panel Connections There are a total of eighteen connectors on the front panel (excluding the RS-232C and power inlet connectors), and all will accept a standard banana plug. Eleven of the front panel banana jacks are recessed and insulated for safety at high voltages. The remaining seven jacks are of a type suitable for high-current applications. The following paragraphs describe the functions of each of these connectors. 3.2.1 Chassis Ground A ground lug, located in the lower right-hand corner of the front panel, is connected to the instrument chassis, and also to the safety ground lead of the AC power connector. When the Model 931A is operated with the power line cord connected, the chassis of the instrument will be connected to the safety ground for the ac outlet. However, when operated from the internal battery with the power cord disconnected, the chassis will be floating. 13

chassis to be tied to a safety ground, especially during battery operation. CAUTION: The front-panel ground terminal should always be connected to the safety ground for the circuit under test. This is especially critical for operation with the line cord unplugged, since the AC line input safety ground will not be connected. 3.2.2 Voltage Inputs The Model 931A features four, front-panel inputs, which can be used for measurement of AC or DC voltages. These inputs are labeled “A”, “B”, “C”, and “N” (for phase A, phase B, phase C, and Neutral, respectively). All four of the inputs utilize identical circuitry, which allows for measurement of voltages up to 750 Vrms or 1000 Vdc between inputs. The 1 megohm input voltage dividers are tied to a common point. Any unused voltage inputs will float at the average value of the used inputs. Safety-insulated banana jacks are used for the connections. Measure voltage between any two of the inputs (e.g., “A” and “N”). Also, the 931A will measure voltage between the input and a synthesized neutral, which is the average of the voltages at inputs A, B, and C. 3.2.3 Current Inputs The Model 931A has three inputs for use in AC current measurement. Each of the inputs uses a pair of five-way binding posts, and has a maximum current capability of 20 amps rms. For each pair of terminals, the left-hand side is positive, and the right-hand side is negative. For measurement of 3-phase neutral current, the neutral signal (In) is available on Channel 2. (3.1) In = −(Ia + Ib + Ic) 14

sharing a common return. One input permits mea- suring a transducer voltage output and the other permits measuring a transducer current output. Make connections via insulated banana jacks. For safety, the measurement-input section is electri- cally isolated from the instrument chassis and all other inputs. A transducer can be tested “live” in a circuit, or using an external source. The transducer inputs are connected to the Model 931A voltage or current measurement channels, and the transducer output is connected to the Model 931A transducer measurement input, except for Custom Pulse, which uses the Timer Input. For details on transducer testing, refer to Section 3.8. 3.2.5 Timer Inputs ������� ������ ��������� ���� � ��� � � ����� Two timer inputs are provided via two pairs of insulated banana jacks, with the inputs being independently and optically coupled. The timer is designed for testing of protective relays, and other similar or related tasks. 3.3 Front Panel Keys The following paragraphs describe the functions and features that can be accessed via Front Panel Keys. The functions of the keys in the main keyboard are divided into three groups: Main Functions, Secondary Functions, and Data Entry Functions. The Secondary and the Data Entry Functions differ from the Main Functions in that they must be preceded by another keystroke (either the shift key, or one invoking a selection menu). There is also a separate group of three keys having functions associated with the control of the internal timer. The functions of these keys are referred to as Timer Control Functions. 3.3.1 Main Functions The primary functions of the front panel keys are described below. The text located directly below each key identifies its primary function. Press the key once to access these primary functions. 15

the signals routed to Channels 1 and 2. The input multiplexing circuitry determines which input signals are connected to the measurement channels, according to selections made by the operator (see Sections 3.5.1.2 and 3.5.2.2). Press the VOLTS/AMPS key again to produce a tabular display showing the signals routed to Channels 1 and 2. Also present is a graphical display of the phase angle. Tabular values, including phase, Watts, VARs, VA, Lead or Lag and frequency (Hz) are located on the right side of the display. Make amplitude measurements with the instrument in either the narrow-band mode (fundamental only), or wide-band mode (true rms). In wide-band mode, the square root of the average of the squared instantaneous sampled values determines the true rms amplitude. It includes harmonics up to 3.05 kHz and removes DC prior to calculation. In narrow-band mode, an extremely accurate, proprietary digital signal processing (DSP) algorithm determines the fundamental amplitude. It also excludes the effects of DC, harmonics and noise. 3.3.1.2 Phase/Frequency ������ � ����� ��������� Press the PHASE/FREQUENCY key to display the frequency of the input signal routed to measurement Channel 1, and the phase angle of the signal routed to Channel 2 (relative to the signal on measurement Channel 1). The input multiplexing circuitry determines which input signals are connected to the measurement channels, according to selections made by the operator (see Sections 3.5.1.2 and 3.5.2.2). Phase angle and frequency are always measured using narrow-band fundamental DSP techniques, guaranteeing accurate measurements in the presence of harmonics, noise, and DC offsets. The displayed phase angle is that of the fundamental component only. 16

angle may also be chosen to be positive or negative by convention. Select your preferred phase convention as described in Section 3.3.1.13, under Menu. See Figure 3.1 for Phase Angle definitions. 3.3.1.3 Power/Vars ������ � ����� ���� Press the POWER/VARS key to display active and reactive power for the combination of signals routed to Channels 1 and 2. The input multiplexing circuitry determines which input signals are connected to the measurement channels, according to selections made by the operator. (see Section 3.5.1.2). To use the POWER/VARS function, Channel 1 must be set to measure AC voltage, and Channel 2 must be set to measure AC current. In wide-band mode, active power (watts) is measured by taking the average of the products of the instantaneous values of voltage and current, including the effects of harmonics. Reactive power (Vars) is measured by taking the vector difference of the wide-band apparent power less the active power (active power is described above). The wide-band apparent power is the product of the wide-band rms voltage and the wide-band rms current. (3.2) Wide − band V ARs = � V A2 + W 2 Mathematically, reactive power is defined as the square root of the quantity apparent power squared minus active power squared. The sign of the wide-band reactive power is determined from the sign of the narrow- band reactive power. In narrow-band mode, active power (Watts) is measured by multiplying the fundamental voltage and current magnitude and the cosine of their phase angle, all determined accurately by DSP. Harmonics are ignored. Narrow-band reactive power (Vars) is measured by multiplying the funda- mental voltage and current by the sine of negative of the fundamental phase angle, all determined accurately by DSP. Again, harmonics are ignored. (3.3) Narrow − band V ars = Vfund × Ifund × Sin(−Θ) Press the POWER/VARS key a second time to toggle the display from Power to Energy. Both Watt-hours and VAR-hours are continuously accumulated. Use the RESTART key to zero the Energy readings. Power 17

produce Energy readings. 3.3.1.4 VA/PF ������ � �� �� Press the VA/PF key to display the apparent power and power factor for signals routed to Channels 1 and 2. The input multiplexing circuitry determines which input signals are connected to the measurement channels, according to selections made by the operator (refer to Section 3.5.1.2 and 3.5.2.2). To use the VA/PF function, Channel 1 must be set to mea- sure AC voltage, and Channel 2 set to measure AC current. Measurements may be made in either wide-band or narrow-band mode. The power factor range is between -1 and +1, leading or lagging (see Figure 3.1). In wide-band mode, apparent power (volt-amps, or VA) is determined by multiplying the wide-band rms voltage by the wide-band rms current. Power factor is determined by dividing the wide-band active power by the wide-band apparent power (refer to Section 3.3.1.3). In narrow-band mode, apparent power is determined by multiplying the fundamental amplitude of the voltage and the current (accurately by DSP). Power factor is the cosine of the phase angle between the fundamentals of the current and the voltage, ignoring harmonics. The Lead/Lag indication for Power Factor may be disabled. Refer to Section 3.3.1.13, Menu - Phase Preference. Pressing the VA/PF key a second time toggles the display from Power to Energy. VA-hours are continuously accumulated. Use the RESTART key to zero the Energy readings. Power readings are summed once every second, using the real-time clock, to produce Energy readings. 18

�� �� ��� ���� �� � � �� �� ����� �� ���� ��� �� ������ ��� ���� � ������� � �� �� � ������ �� �� ������ �� ���� ��� �� � ��� ����� �� ����� �� �� �� �� � ������ �� ����� �� � ������ ��� ����� � ������ � �� �� � ������� � �� ����� �� ���� ��� � �� ��� ���� �� � � �� � �� ����� �� ����� ��� � ������ ���� ���� �� ������� � �� �� � ������ �� �� ����� �� ���� ��� �� ������� ���� ���� �� ������ � �� � � ������ � �� ����� � ���� ��� �� �� ���� ���� � ����� � �� �� � � ������� ���� ������� �������� ������ ������� ����������� ����� �� ��� ���� ������ ��������� ���� ��� ��� �������� ��� ���� �� ������� ���� � ������� ������������ ����� ������ � ��� � ����� � ������ � ������ �� ���� ���� ����� � ����� � ������ � ���� � ��� � ������ � ����� ������ �������� � ����� ����� ������� ������� ���� �������� �� �������� ������ ��������� ���� ������� ��� ������� �������� ���������� ����� ������ � �������� ��� � ���� � ���� � � � ���� �� ��� � � � � �������� ������ ������ �� ���� � � Figure 3.1: Phase, Power Factor, and VAR Definitions 19

�������� ������ ����� ��������� �������� ������ ������ ��������� �������� ������ ����� �������� �������� � � �� � �� ������ � � �� � � � �� � � � � �� ��� � � � � � �� �������� ��� � ���� � � � � � � � �� � �� � � �� � � �� � � ������ ����� ������� �������� ��� ������ ����� ������� ��������� ��� �������� ����� ������ �������� ��� �������� ����� ������ ��������� ��� ����� ������ ���� ������ ������ ���� ����� ������ ����� ����� ������ ����� Figure 3.2: Phase, Power Factor, VAR Quadrants Phase Convention Quadrant I Quadrant II Quadrant III Quadrant IV CH2 Lagging CH1 (-) for ±180◦ 0◦ to -90◦ -90◦ to -180◦ +180◦ to +90◦ +90◦ to 0◦ (+) for ±180◦ 0◦ to +90◦ +90◦ to +180◦ -180◦ to -90◦ -90◦ to 0◦ (-) for 0 - 360◦ 360◦ to 270◦ 270◦ to 180◦ 180◦ to 90◦ 90◦ to 0◦ (+) for 0 - 360◦ 0◦ to 90◦ 90◦ to 180◦ 180◦ to 270◦ 270◦ to 360◦ Table 3.1: Phase Angle Preferences Phase angle of Channel 2 (current) relative to Channel 1 (voltage) Lagging Current – An alternating current which, in each half-cycle, reaches it maximum value a fraction of a cycle later than the maximum value of the voltage that produces it. 20

magnitude of individual harmonics for the signals routed to Channels 1 or 2. The input multiplexing circuitry determines which input signals are connected to the measurement chan- nels, according to selections made by the operator (refer to Sections 3.5.1.2 and 3.5.2.2). Harmonics up to the 50th are shown for fundamentals of 50 or 60 Hz. At 400 Hz, only harmonics up to the 7th are displayed, due to the instrument bandwidth limitation of 3.05 kHz. Harmonics are measured by first determining the AC fundamental and the DC components of the signal, and removing them algebraically from the digitized waveform. For the spectral display, K-factor, and individual harmonic measurements, Fast Fourier Transform analysis determines the residual. Dividing the rms of the residual by the wide-band rms amplitude determines the Total Harmonic Distortion (THD). With these techniques, harmonic measurement accuracy is not dependent upon fundamental frequency. Select any harmonic with the movable cursor found in the graphic display using the arrow keys. The display also shows corresponding numerical values of the amplitude and the phase angle of the harmonic relative to fundamental. Press CHANNEL 1 SELECT or CHANNEL 2 SELECT to toggle the display between the signals applied to Channels 1 or 2. Numerical display of THD and K-factor are always available. THD is the rms of the residual, including noise and spurious signals, as a percent of the wide-band rms. K-factor is the rms sum of the fundamental plus the individual harmonics (each weighted by the square of the harmonic number) expressed as a ratio to the fundamental. It is an estimate of the heating effect of harmonic energy in magnetic materials. K-factor is used to determine transformer de-rating. K-factor is 1.0 for a perfect sine wave and greater than 1.0 with distortion. 3.3.1.6 Waveform ������ � �������� ����� Press the WAVEFORM key to view a graphic display of the waveforms for the signals, which are routed to Channels 1 and 2. The input multiplexing circuitry determines which input signals are connected to the measurement channels, according to selections made by the operator. 21

they have been digitized and subjected to digital low-pass filtering. The display includes all components of the signal up to 3.05 kHz. The waveform display is normalized to positive going zero crossings of Channel 1 signal fundamentals. To inspect the current waveform, reference the current at Channel 2 to the voltage at Channel 1. The displayed waveform amplitude is relative to the displayed percentage of the selected range. View waveforms individually by pressing CHANNEL 1 SELECT, or CHANNEL 2 SELECT, with the waveform display active. 3.3.1.7 Channel 1 Select �������� � ������ ����������� Press the CHANNEL 1 SELECT key to view the input config- uration menu for Channel 1. Always connect the lowest distortion input signal to Channel 1 since it is used as the internal reference. For most power systems the voltage has lower distortion than the current. If applying only one signal, it must be connected to Channel 1. If analyzing a single highly distorted waveform connect a reference signal of the same fundamental frequency to Channel 1 and the waveform to be analyzed to Channel 2. Combinations from the front panel inputs allow twenty-seven choices; three AC currents (A, B, C); twelve AC voltages, and twelve DC voltages. Each voltage terminal may be referenced to any other voltage terminal, to the front-panel neutral, or (for AC) to a synthesized neutral, which is the average of “Va”, “Vb” and “Vc”. Tables 2.1 and 2.2 list the possible input combinations. 3.3.1.8 Channel 2 Select �������� � ������ ��������� Press the CHANNEL 2 SELECT key to select the input con- figuration menu for Channel 2. Front panel input combinations allow twenty-eight choices; four AC currents (A, B, C, N); twelve AC voltages, and twelve DC voltages. The Neutral Current “N” is minus the vector sum of “Ia, Ib, and Ic”. Each voltage terminal may be referenced to any other voltage terminal, to the front-panel neutral, or (for AC) to a synthesized neutral, which is the average of “Va”, “Vb” and “Vc”. Tables 2.1 and 2.2 list the possible input combinations. 22

process and hold the instantaneous value of each measured parameter. With the exceptions of harmonics, waveform and 3- phase, any display function may be selected during the time that the measurement hold mode is active, and the corresponding values observed. Harmonics, waveform, or 3-phase information may only be displayed if the instrument was in that respective mode when the MEASURE/HOLD key was pressed. Press the MEASURE/HOLD key again to leave the Measurement Hold mode and resume measurements. The display indicates whenever the Measurement Hold mode is active. Two other methods of activating the Measurement Hold mode is by reviewing Logged Data, or by the Timer Stop Gate (see 3.7.2.5). 3.3.1.10 CH2 Range ��� ����� ���� ����� Press the CH2 RANGE key to select the operating voltage or current range for Channel 2. The ranges are only approximate and vary from unit to unit. Range values allow selection of either auto range, or a fixed range made available from one of the following groups (depending on the input mode selected): 0 – 3.5 12 – 28 96 – 224 3 – 7 24 – 56 192 – 448 6 – 14 48 – 112 384 – 750 Table 3.2: Channel 2, AC Voltage Ranges, Vrms 0 – 0.09 0.32 – 0.75 2.56 – 5.97 0.08 – 0.18 0.64 – 1.49 5.12 – 11.9 0.16 – 0.37 1.28 – 2.98 10.24 – 20.0 Table 3.3: Channel 2, AC Current Ranges, Arms 0 – 5 17 – 40 135.8 – 320 4.2 – 10 34 – 80 271.5 – 640 8.5 – 20 68 – 160 543 – 1000 Table 3.4: Channel 2, DC Voltage Ranges, Vdc 23

��� ��� ������� Press the MIN/MAX key to display the minimum, maximum and average values for any and all measured parameters. Accumulation of 3-phase minimum and maximum parame- ters occur only while the 3-phase display is active. The MIN/MAX/AVERAGE feature continuously updates the mini- mum, maximum and average values stored since initial power-on. During display of a parameter, any new value exceeding the currently stored minimum or maximum will overwrite it. Averaging is continually updated during the measurement period. Accumulation of data can also be re- initiated, by pressing the SHIFT key, then the RESTART key. Pressing the MIN/MAX key repeatedly scrolls between minimum, maximum, average and present data. 3.3.1.12 Transducer ���������� ������ Press the TRANSDUCER key to show measurements taken at the front-panel transducer voltage and current inputs. Config- ure the Model 931A to display the transducer-input magnitude as either the actual measured quantity or as a percentage of full scale. Likewise, display the transducer output level as either the measured quantity or percentage of full scale, or as a percent error (based on the input and output ranges). Prior to initiation of Transducer measurements, the Model 931A automatically performs a self-calibration. 3.3.1.13 Menu ���� ���� Press the MENU key to display a configuration menu used to define configurable parameters within the Model 931A. The sub- menus and functions available from the MENU key are defined as follows: ˆ RS-232 Port Setup: Used to set the baud rate, data bits, stop bits, parity, and flow control for the RS-232C communications port. ˆ Set Real-Time Clock: Set the Year, Month, Day, Hour, Minute, Second, and also the Daylight Saving mode. ˆ Backlight and Auto-Shutdown: Select the operating mode for the display backlight and for the Auto-Shutdown function. The Auto-Shutdown function will turn the instrument off if there are no input signals or keystrokes for approximately 10 minutes. 24

display. This includes whether phase angle is displayed as ±180◦ or 0−360◦ and (–) for Channel 2 lagging Channel 1 or (+) for Channel 2 lagging Channel 1. The Phase Preference selection only affects the displayed phase angle and no other quantities. Section 3.6.1 describes the phase convention selection. There is also a selection for enabling or disabling the Power Factor “Lead/Lag” display. ˆ Print Selections: Allows selection of the type of data to be printed or exported when pressing the PRINT key. A complete description of the printing function is contained in Section 3.11. ˆ Print Broadcast Mode: Allows automatic output of the selected print option at various time intervals. ˆ Auto-Log Setup: Shows up only when 16-Mbyte memory card is installed. See Section B.3.4 for details. 3.3.1.14 Log Data ���� ���� ������ Press the LOG DATA key to store measurement data to non- volatile memory. Stored data includes current time and date, according to the built-in real-time clock. The memory location in which data is stored will be indicated momentarily in the lower right corner of the display. Displays a diagnostic message if the memory is full. See Section 3.10 for details of data logging features and controls. For a Model 931A equipped with extended memory, see Section B.3. 3.3.1.15 Print ����� ������ ��� Press the PRINT key to transmit the current measurement data to a printer, modem, or computer connected to the RS-232 port. See Section 3.11 for a complete description of printing functions. 25

what it was immediately prior to the last change. It may be used to undo an unwanted change, or to toggle between two different setups. When LAST SETUP is pressed, the current state is also stored as the new LAST SETUP. 3.3.1.17 Ch1/Ch2 ��� �� ��� ����� Press the CH1/CH2 key to display the magnitude and phase of the signal at Channel 1 divided by the signal at Channel 2. Depending on the input signals selected, the displayed units for magnitude will be either ohms (Channel 1 voltage and Channel 2 current), mhos (Channel 1 current and Channel 2 voltage), or P/U (both channels the same). The value shown for phase represents the phase angle between the signal at Channel 1 and the signal at Channel 2. It is displayed in accordance with the phase convention defined for the instrument (see Section 3.6.1.3). When using the CH1/CH2 function, any scaling factors for magnitude and/or phase will apply to the displayed result (see Section 3.3.2.17 for a discussion of scaling factors). CH1/CH2 is useful for checking the amplitude and phase angle ac- curacy of current transformers. Connect the primary in series with a Model 931A current input and set that input to Channel 1. Connect the transformer secondary to another current input and set that input to Channel 2. Set the scale factor for the CT input (see Section 3.3.2.17) and press CH1/CH2. Using an external source, supply the appropriate level current. 3.3.2 Secondary Functions The secondary functions of the front panel keys are shown below. They are identified by the text located directly above each of the keys, and are highlighted in gray. Access these functions by pressing SHIFT prior to pressing the desired key. 3.3.2.1 Shift Press the SHIFT key to access the functions in the shaded gray areas above the keys. An indicator in the display shows when the SHIFT key has been pressed. Press SHIFT a second time to prevent access to the secondary functions. 26

Up to six different instrument configurations can be stored for future measurements using STORE SETUP (see Section 3.3.2.16) and recalled by first pressing SHIFT and then the applicable SETUP 1 through SETUP 6 front panel key. The stored setup information includes Channel Selection, CT/PT Scale Factors, Transducer and Timer Configurations. Setup keys do not enable SCALE factors, and are shown below. ������ � ����� ���� ������ ������ � ����� ��������� ������ � ����� ���� ������ � �� �� ������ � ��������� ������ � �������� ����� 3.3.2.3 Narrow Band �������� � ������ ����������� Press the NARROW-BAND key to change the measurement mode for amplitude and power quantities to measure the fun- damental frequency only. The system uses proprietary DSP algo- rithms in which harmonics are ignored. Refer to the help screens for each individual measurement for more detailed descriptions. Channel 1 is used as the internal reference. Use Channel 1 if only one signal is measured. If measuring both a current and a voltage, use Channel 1 for measuring the voltage and Channel 2 for the current. 3.3.2.4 Wide Band �������� � ������ ��������� Press the BAND-WIDE key to change the measurement mode to wide-band for amplitude and power quantities; this includes all frequencies up to 3.05 kHz. For more information, refer to the help screens for each individual measurement. 3.3.2.5 Measure 3 Phase ������� ���� ����� ������ Press SHIFT, then MEAS 3 PHASE to display the 3-phase mea- surement selection window. MEAS 3 PHASE permits the Model 931A to make sequences of measurements on sets of voltage and current inputs. The measured set of input combinations depends on the 3-phase measurement selection chosen (see Figure 3.3). 27

To select the appropriate measurement mode, move the cursor to the desired mode and press ENTER. The input pairs shown in parenthesis are those used for the TABULAR display. The Model 931A displays the following display selection menu when you press ENTER: Figure 3.4: Three Phase Display Selection 3.3.2.6 Tabular Display The 931A makes a sequence of measurements as shown in the 3-phase Measurement Selection menu. Amplitude, power and phase quantities for the individual phases are shown along with the totals for the system. In the right column, the screen identifies totals by a “T”, energy readings by “H” and as averages by a “*”. The sample Tabular display below identifies the individual quantities. Values for Va and Ia Values for Vc and Ic Combined Values Phase Sequence Indication Average Voltage Average Current Average Phase Total Active Power Total Reactive Power Total Apparent Power Average Power Factor/lead/lag Measurement Indicator Mode Indicator ABC Figure 3.5: Three Phase Tabular Display 28

“Van,Ia” and “Vcn,Ic”. This is useful for making measurements on split- phase systems. The column on the far right shows the averages for voltage, current, phase and the totals for power quantities. The columns for “A” and “C” show the voltage; characters in the lower right-hand corner of the display alternate between “VanIa” and “VcnIc”, indicating the current measurement. In 3-phase 3-wire 2-element mode, the instrument alternates between measurements of “Vab,Ia”,“Vcb,Ic”,“Vac,Ib”, and “Vcb,Vab”. It com- putes “Vac” and includes it in the 3-phase average voltage. While Ib is measured, it is not included in the 3-phase results. This procedure yields accurate results for active power, but to estimate apparent power, a correction of 0.866 must be arbitrarily applied since accuracy depends on the symmetry of the phase voltages. “VcbVab” phase is measured to determine phase rotation. In 3-phase 3-wire 3-element mode, the instrument sequences between measurements of “Vas,Ia”, “Vbs,Ib”; and “Vcs,Ic” (“s” denotes synthe- sized neutral, which is the average of the signals present at voltage inputs “a”, “b”, and “c”). Results are accurate for active power, but to estimate apparent power synthesized neutral is used, and accuracy depends on symmetry of the phase voltages. Reactive power, power factor, and phase angle also are estimated. “VasVbs” phase is measured to determine phase rotation. In 3-phase 4-wire, 3-element mode, the instrument sequences between measurements of “Van,Ia”, “Vbn,Ib”, and “Vcn,Ic”. All results are accurate. This is the preferred mode for 3-phase measurements when neutral is available. Phase rotation is determined by measuring “VanVcn”. In 3-phase 4-wire 2.5 element mode, the instrument sequences between measurements of “Van,Ia”, “Vb,Ib”, “Vcn,Ic”, and “VcnVan”. NOTE: The “B” voltage input must be externally connected to the “N” voltage input. “Vb” is internally generated using the synthesized neutral circuit, and the accuracy of all results depends on the symmetry of the phase voltages. In all three-phase modes, the Model 931A also measures and displays phase the sequence, “ABC” or “CBA”. (see Figures 3-2 and 3-3). A phase measurement of “Vab to Vac” is made at the end of each sequence. If the “Vab to Vac” phase is negative, the sequence is “ABC” otherwise it is “CBA”. Phase Sequence may be checked using the waveform display. 29

display will show the peak of “Vbn” 120 degrees after the peak of “Van” for an “ABC” Phase Sequence. The waveform display always begins at the zero crossing of the Channel 1 signal. Dashes displayed for the phase sequence indicate that the Model 931A could not measure a valid “Vab to Vac” phase. Phase rotation is determined by measuring “VcnVan”. The second tabular display (Watt/VAR/VA Hour) replaces the total power quantities with accumulated energy readings. The energy readings are set to zero by pressing the RESTART key. 3.3.2.7 Vector Diagram The Vector Diagram consists of a table of the measured voltages, currents and phase angles along with their vector representation. The “A” phase voltage vector is fixed in the horizontal direction. Positions of all other vectors rotate according to their phase angle with respect to the “A” phase voltage. Positive phase angle is denoted by counter-clockwise rotation. The length of the vectors shows the relative amplitude of each phase. The largest voltage and the largest current each have the longest vectors. A vector with a length of less than one pixel is not displayed. All voltage and current phases are made with respect to the “A” phase voltage. The “A” phase voltage must be present for a proper Vector Diagram display. 3.3.2.8 Voltage and Current Sequence The Voltage and Current Sequence display shows the measured voltages, currents and phase angles in the top portion of the display. The bottom half of the display shows the positive (V1, I1), negative (V2, I2) and zero (V0,I0) sequence values. The Model 931A defines the positive sequence as the values in the “ABC” direction and negative sequence as values in the “CBA” direction. Also included is a computed value for the neutral current amplitude and phase angle. All voltage and current phases are made with respect to the “A” phase. The “A” phase must be present for a proper Voltage and Current Sequence display. Positive-Sequence Current (I1) and Voltage (V1) are the normal com- ponents represented in balanced three-phase (3-wire and 4-wire) systems. They are present in operating motor and generator windings. Negative-Sequence Currents (I2) and Voltages (V2) are the components in 3-phase systems that result from unbalanced phase-to-phase current and voltage. They cause undesired heating in motor and generator windings. Reversed phase sequence – ACB vs ABC – can be viewed as an extreme negative sequence case. 30

unbalanced 3-phase four-wire systems, and correlate to “neutral shift”, where there is a current and potential difference in motor or generator windings with respect to system ground. Zero-Sequence conditions result from unequal phase-to-neutral parameters. 31

Vector Diagram Voltage and Current Sequence Waveform Figure 3.6: Three-Phase Displays for an ABC System 32

Vector Diagram Voltage and Current Sequence Waveform Figure 3.7: Three-Phase Displays for a CBA System 33

������ ���� � �� �� Figure 3.9: 1-Phase, 3-Wire, 2-Element Connections 34

������ ���� � �� � � Figure 3.11: 3-Phase, 4-Wire, 2.5-Element Connections 35

36

current range for Channel 1. The ranges are only approximate and vary from unit to unit. Press SHIFT then the CH1 RANGE key to view a menu showing a selection of auto range or a fixed range. The following fixed range groups are available: 0 – 3.5 12 – 28 96 – 224 3 – 7 24 – 56 192 – 448 6 – 14 48 – 112 384 – 750 Table 3.5: Channel 1, AC Voltage Ranges, Vrms 0 – 0.09 0.32 – 0.75 2.56 – 5.97 0.08 – 0.18 0.64 – 1.49 5.12 – 11.9 0.16 – 0.37 1.28 – 2.98 10.24 – 20.0 Table 3.6: Channel 1, AC Current Ranges, Arms 0 – 5 17 – 40 135.8 – 320 4.2 – 10 34 – 80 271.5 – 640 8.5 – 20 68 – 160 543 – 1000 Table 3.7: Channel 1, DC Voltage Ranges, Vdc When an input signal exceeds the upper limit of a range which is held, the numbers in the display will change to dashes, and the message ”Channel 1 Overload” will appear. 3.3.2.11 Restart ��� ��� ������� Press the RESTART key to erase minimum, maximum and average values previously stored and begin recording new ones. Pressing RESTART will also reset Energy values to zero. 37

and output ranges; it affects the testing of transducers. The Model 931A can be set to automatically calculate and display transducer error as percent of full scale, when the same input signal is applied to the transducer under test and the Model 931A. Any calibrator or load box with source may be used, or transducers may be calibrated in-circuit. Press the CONFIG key to view the following menu: Use the arrow keys to select a menu item, then press ENTER. Selections made from this menu will activate other sub-menus, which allow for various transducer-test configurations. Once all parameters have been set, press ESCAPE and Transducer Operation will begin. See Section 3.8 for further information on transducer testing. 3.3.2.13 Help ���� ���� Press SHIFT then the HELP key to find reference information about the functions of the Model 931A. To get help for a specific function, press SHIFT, then HELP, followed by the key for the desired function. Use the up and down arrow keys to page through the help message; press the ESCAPE key to return to normal operation. Display a menu featuring help topics for general operation by pressing SHIFT then HELP twice (i.e. SHIFT/HELP/SHIFT/HELP). 3.3.2.14 Review ��� ���� ������ Press SHIFT then REVIEW to view a menu of stored records. An example display is shown below: 38

reviewed 2. Press ENTER to view the highlighted record. After pressing ENTER, the unit goes into measurement hold mode and the stored record overwrites the current data. See Section 3.10 for further in- formation on data logging and reviewing. Press MEASURE/HOLD to release the instrument from the measurement hold mode. 3. When in the selection menu display, press the left arrow key to clear the highlighted record from memory. 4. To remove all data records from memory, press ENTER when Clear All Entries is highlighted. 5. Press escape to return the instrument to normal operation with out any modification of stored data. 3.3.2.15 Print Log ����� ������ ��� Press SHIFT then PRINT LOG to print to a list of the stored records to printer or computer connected to the serial interface (RS-232 port). 3.3.2.16 Store Setup ���� ����� ������ ����� Use the STORE SETUP key to save the current instrument- state in one of six memory registers: SETUP 1 through SETUP 6. Press SHIFT then STORE SETUP to produce the following prompt on the display: Press SHIFT and desired SETUP key to store current instrument-state. Press SHIFT, followed by one of the six SETUP keys (highlighted in gray across the top row) to store the current instrument setup into the corresponding register (SETUP 1 through SETUP 6). All setups are stored in non-volatile memory. For instructions on recalling instrument setups, see Section 3.3.2.2. 3.3.2.17 Scale ��� � ��� ����� Use the SCALE key to apply individual Scale Factors to each AC measurement input function. Scale Factor corrections can adapt the Model 931A for use with current or potential transformers. 39

and account for the ratio of a CT or PT. Amplitude and phase scale factors may be entered for: ˆ Each of the three current inputs; ˆ Each of the three voltage inputs relative to neutral; ˆ The three voltage inputs relative to each other. Use the store SETUP FUNCTION described in Section 3.3.2.16 to store global PT and CT scale factors (not individual) for later retrieval. The following assignments are made: Set Scale: Auto Sets: Set Scale Auto Sets: Van Vas, Vb Vbc Vcb Vbn Vbs Vca Vac Vcn Vcs Ia In Vba Vab SCALE does not allow scale factors to be entered for DC measurements. Press SHIFT > SCALE to view Scale Factor Gain and Phase Selections. The display then shows the magnitude and phase scale factors for each of the input functions as seen below. For magnitude, the factor represents the number by which a measured value is multiplied during the measurement process. For example, a magnitude scale factor of 100, with 10 volts applied to the Model 931A input, displays 1000 volts. Therefore, if the Model 931A was used to measure the voltage at the output of a 100:1 PT, and the magnitude scale factor was set to 100, the display would show the actual voltage value present at the PT input (compensating for the 100:1 reduction of the PT). Valid range for Scale Factors is 999999 to 0.0001. Apply global PT and CT scale factors and simplify operation when desiring to use a PT or CT on any input. For example, press SHIFT > SCALE, then select PT with the cursor, then press ENTER. Using the cursor, select the appropriate digit, or decimal point, using the right and 40

numerical digit, or decimal point, and press ENTER. After the changing the PT and CT values, move the cursor to PT/CT ON, and press ENTER. When done, this applies the new scale factors for PT and CT to every input, and blocks out the individual scale factors shown for Vxy and Ix. Phase angle scale factors indicate the offset, in degrees, that will be added to the input signal before it is displayed. Additionally, these offsets apply only at the fundamental frequency of the signal. In the harmonic display mode, phase offsets equal the offset at the fundamental frequency multiplied by the chosen harmonic number. Enable or disable individual scale corrections globally using the SCALE menu (see Scale Factor Screen above), bottom line. Measurements made in wide-band mode use digital true-rms detection. Phase corrections are applied for power quantities by using complex multiplication. The accuracy of this method depends on the absence of significant harmonic power and the size of the phase offset. 3.3.3 Data Entry Functions When performing operations, which require modification of parameters or making selections from menus, the arrow keys in the top row of the keyboard are used for cursor movement as described in the following paragraphs. The general procedure for selecting items from a menu is to use the arrow keys to move the cursor (arrow symbol) to the desired selection and press the ENTER key. If the menu selection was a number to be modified, the cursor (flashing underline) will appear under the digit to be modified. Use the right/left arrow keys to select the digit to be modified. Use the up/down arrow keys to cycle the digit (+, ,., 0, 1, 2, 3, 4, 5, 6, 7, 8, 9). Press ENTER when the number is correct. The plus, minus and decimal point will only be included in the cycle where appropriate. 3.3.3.1 Nomenclature ������ � ����� ��������� ������ � ����� ���� ������ � �� �� ������ � ��������� ������ � �������� ����� ������ � ����� ���� ������ 41

movement function associated with this key is automatically enabled when required. After making a menu selection, this key will return to its primary function. 3.3.3.3 Down Arrow Use the down arrow key to move the display cursor down. The cursor function associated with this key is automatically enabled as required. After making a menu selection, this key will return to its primary function. 3.3.3.4 Up Arrow Use the up arrow key to move the display cursor up. The cursor movement function associated with this key is automatically enabled when required. After making a menu selection, this key will return to its primary function. 3.3.3.5 Right Arrow Use the right arrow key to move the display cursor right. The cursor movement function associated with this key is automatically enabled as required. After making a menu selection, this key will return to its primary function. 3.3.3.6 Enter Press the ENTER key to make menu selections and accept modified numbers. 3.3.3.7 Escape Press the ESCAPE key to back-out of menus or selections. While not necessary to precede ESCAPE with SHIFT, ESCAPE is automatically available when applicable. Also, use ESCAPE to terminate the display of waveforms, 3-phase, harmonics, or XMODEM file transfers. To view the sign-on message, press and hold the ESCAPE key while the Sign-On message is being displayed; release to continue. 3.3.4 Timer Control Functions Three keys, located left of the timer connection terminals, control opera- tion of the internal timer. The functions of these keys are described below. 42

the time measurement, the timer function and trigger modes. An example is shown below. In the main timer display, FUNCTION shows the parameter that the timer is configured to measure. TRIGGER A and TRIGGER B describe the actions, which will constitute valid triggers for the “A” and “B” inputs. 3.3.4.2 Config Press the CONFIG key to display the timer configuration menu, which appears as follows: One or more sub-menus follow each of the menu selections, which allow configuration of the specific functions. Section 3.7 provides more detailed information about the timer sub- menus and their functions. 3.3.4.3 Arm/Reset Use the ARM/RESET key to arm and reset the active timer. Once stopped, pressing the ARM/RESET key will reset the timer. Pressing it a second time arms the timer for next cycle. The ARM/RESET function may also be used to manually stop the timer during a measurement cycle. 43

The Model 931A uses a supertwist liquid-crystal display with a resolution of 240 horizontal pixels by 64 vertical pixels. In most cases, both mea- surement channels simultaneously display information from measurements and some instrument configuration. The display has a bright CCFL backlight available for low ambient light situations. See Section 3.3.1.13 Menu, Backlight and Auto-shutdown control, for directions on using the backlight. Use of the backlight significantly increases the battery drain. Display changes in response to keystrokes allow selections from multiple menu levels, resulting in a self-prompting interface. 3.5 Direct Measurements For measurement of certain parameters, the Model 931A computes results from one or both channels individually. Always use Channel 1 if only one input signal is present. These measurement parameters include the following: ˆ AC Voltage ˆ AC Current ˆ DC Voltage ˆ Frequency ˆ Harmonics ˆ Waveform The following sections provide instructions for performing measure- ments of parameters within this group. 3.5.1 AC Voltage Measurement The Model 931A can measure and display AC voltages of up to 750 Vrms. 3.5.1.1 Input Connections Four inputs, labeled “A”, “B”, “C”, and “N” are available for measuring AC voltage, and each uses identical circuitry. Input multiplexing circuitry allows measurement of the value at inputs “A”, “B”, or “C”, relative to any other input. For example, to measure a voltage between terminals “A” and “N” simply connect the leads to those two terminals. 44

between voltage inputs and chassis ground lug. Make all measurements between two (or more) of the voltage inputs. The ground lug is included for safety purposes only, especially during battery operation. See Sec- tion 3.2.1. 3.5.1.2 Configuring the Channels Configure the chosen measurement channel after connecting the voltage to the appropriate input terminals. If measuring only one AC voltage (e.g. single-phase), use Channel 1, since this channel is used for frequency measurements. Press the CHANNEL 1 SELECT key to configure the measurement channel and to display the following menu: Arrows form the cursor, highlighting one of the selections. Press the arrow keys to locate the measurement value. For example, using the arrow keys move the cursor to Van to measure an AC voltage between inputs “A” and “N”. Press the ENTER key to confirm the selection. Measure two separate voltages concurrently by configuring both Chan- nels 1 and 2. For example, use the selection method above to use Channel 1 to measure “Van” and use Channel 2 to measure “Vcn”. The two voltage signals must have the same fundamental frequency. 3.5.1.3 Performing the Measurement Press the VOLTS/AMPS key to display the measured AC voltage and produce a display similar to the one shown below: The large number at the top of the display indicates the voltage 45

corresponds to the voltage value for measurement Channel 2. The display indicates the general measurement bandwidth near the lower left-hand corner. The Model 931A uses either wide-band or narrow- band mode to measure and display AC voltage. Press the SHIFT key then BAND-WIDE to change the measurement mode to wide-band RMS and include all frequencies up to 3.05 kHz. Press the SHIFT key then NARROW-BAND to measure the fundamental magnitude only, using DSP algorithms; harmonics are ignored. The Model 931A displays dashes for Channel 1 and Channel 2, when in narrow-band mode, if the signal present on Channel 1 is below a value, which can be accurately measured. NOTE: Channel 1 is used as the internal reference; if only one signal is measured, Channel 1 must be used. If both a current and a voltage are measured, Channel 1 should be used for the voltage and Channel 2 for the current. 3.5.2 AC Current Measurement The Model 931A can directly measure and display AC currents of up to 20 Arms. It can measure higher currents using a current transformer (CT) and with direct readout using the scaling feature (see “Scale” in Section 3.3.2.17). 3.5.2.1 Input Connections The Model 931A provides three sets of input connectors for measuring AC current: labeled “A”, “B”, and “C”. All three inputs use identical circuitry and are electrically isolated from all others: the voltage inputs, and chassis ground. The input multiplexing circuitry allows measurement of the value at any one the inputs. The Neutral Current, In = −(Ia + Ib + Ic), is available for measurement on Channel 2. 3.5.2.2 Configuring the Channel Configure the chosen measurement channel after connecting the current to the appropriate input terminals. If measuring only one AC current (e.g. single-phase), use Channel 1, since this channel is used for frequency measurements. 46

options, press the CHANNEL 1 SELECT key. Arrows form the cursor and highlight one of the selections. Press the arrow keys to locate the measurement value. For example, using the arrow keys move the cursor to Ia to measure an AC current at the two “A” terminals. Confirm selection by pressing ENTER. 3.5.2.3 Performing the Measurement Press the VOLTS/AMPS key to display the measured AC current, and produce a display similar to the one shown below: The large number at the top of the display indicates the current value measured by Channel 1. The number below it corresponds to the current value measured by Channel 2. The display indicates the general measurement bandwidth (i.e. Wide- Band) near the lower left-hand corner. The Model 931A uses either wide- band or narrow-band mode to measure and display AC voltage. Select measurement bandwidth by pressing SHIFT, followed by either NARROW-BAND or BAND-WIDE. Press SHIFT then BAND-WIDE to change the measurement mode to wide-band RMS and include all frequencies up to 3.05 kHz. Press SHIFT then NARROW-BAND to measure the fundamental mag- nitude only, using proprietary DSP algorithms. Harmonics are ignored. If the signal at Channel 1 is too low to be accurately measured, when in narrow-band mode, the Model 931A displays dashes for both Channel 1 and Channel 2. 47

The Model 931A can directly measure and display DC voltages of up to 1000 Vdc. 3.5.3.1 Input Connections The Model 931A provides four connectors for measuring dc voltage. Labeled “A”, “B”, “C”, and “N”, all four inputs use identical circuitry. Additionally, input multiplexing circuitry allows referencing the voltage across any two, voltage terminals. For example, to measure a voltage from “A to N”, connect the leads between those two terminals. NOTE: The Model 931A does not have a provision for measurement of voltage between any of the voltage inputs and the chassis ground lug. Make all voltage measurements between two (or more) of the voltage terminals. The ground lug is included for safety purposes only. 3.5.3.2 Configuring the Channels Configure the chosen measurement channel after connecting the voltage to the appropriate input terminals. Configure Channel 1 by first pressing the CHANNEL 1 SELECT key, and the following menu will appear on the display: Arrows form the cursor, and highlight one of the selections. Press the arrow keys to locate the measurement value. For example, using the arrow keys move the cursor to highlight Van to measure a DC voltage between inputs “A” and “N” (“Van” is in the third row up from the bottom). Confirm the selection by pressing ENTER. 3.5.3.3 Performing the Measurement Press the VOLTS/AMPS key to display the measured DC voltage and view a display similar to the one shown below: 48

measured by Channel 1. The display below it corresponds to Channel 2, which is not used in this example. The display indicates the general measurement bandwidth near the lower left-hand corner. However, the bandwidth setting has no effect on DC measurements. 3.5.4 Frequency Measurement The Model 931A measures fundamental frequencies within the range of 20 Hz to 500 Hz. The following paragraphs describe the steps required to perform Frequency measurements. 3.5.4.1 Input Connections The Model 931A can measure the frequency of AC voltages or currents connected only on Channel 1. Make connections in the same manner as for magnitude measurements (see Section 3.2.2 for AC voltages, and Section 3.2.3 for AC currents). 3.5.4.2 Configuring the Channels Frequency measurement is permitted only on signals routed to measure- ment Channel 1. Configure Channel 1 by first pressing CHANNEL 1 SELECT; the following menu will appear on the display: Use the arrow keys to locate the measurement value and press ENTER. For example, using the arrow keys move the cursor to highlight Van to measure an AC voltage between inputs “A” and “N”. For frequency measurement of an AC current at input “A”, select “Ia” in the top row. 49

Press the PHASE/FREQUENCY key to display the measured frequency and produce a display similar to the one shown below: The large number in the middle of the display indicates the frequency of the signal on Channel 1. The indication for phase angle may consist of dashes because only one signal is being input or the signal level is too low, making phase comparison impossible. The display shows dashes when the signal at Channel 1 is below a value that can be accurately measured, indicating that the signal is insufficient. 3.5.5 Harmonic Measurement The Model 931A can measure harmonic content up to the 50th harmonic for fundamental signals of 50 or 60 Hz. Use either Channel 1 or 2 to measure harmonics, but on only one channel at a time. 3.5.5.1 Input Connections Make connections for harmonic measurement in the same manner as for AC voltage or current magnitude measurements. Since the Model 931A derives the harmonic value from the same inputs, simply press the HARMONICS key to view them. See Section 3.2.2 (AC voltages) and Section 3.2.3 (AC currents) for descriptions of AC Input connections. 3.5.5.2 Configuring the Channel(s) To configure the Model 931A for harmonic measurement, press either the CHANNEL 1 SELECT or CHANNEL 2 SELECT key and use the cursor keys to select the measurement signal from the channel menu. The Model 931A measures harmonics on signals processed by either channel. 3.5.5.3 Performing the Measurement Press the harmonics key to display harmonics. By default, Channel 1 initially displays harmonics. To switch between harmonics on either 50

The harmonics display appears as follows: In the example above, the display shows the harmonic content of the AC current at the input of a switching power supply. While all harmonics are shown, only the odd harmonics have enough amplitude to be displayed. The first, vertical bar (on the left) represents the fundamental. An arrow, below the second bar, represents the cursor, and lies under the third harmonic. Move the cursor in increments of 1 harmonic with the right and left arrow keys. Change the vertical scale to better view harmonics with the up and down arrow keys. The harmonic magnitude factor applied from using the up/down arrow keys appears in the upper right corner. The second and third lines of display text describe individual harmonic information, highlighted by the cursor. These values include the following: ˆ The channel being measured ˆ The input configuration for the channel ˆ The harmonic number ˆ The harmonic amplitude as a percentage of fundamental amplitude ˆ The rms amplitude of the harmonic ˆ The phase angle of the harmonic, relative to the fundamental ˆ The frequency of the harmonic The top line of text shows THD and K-factor, which relate to the overall input signal, and do not change when the cursor is moved. The Model 931A analyzes harmonics by first determining the AC fundamental and the DC components of the signal. It then removes them algebraically from the digitized waveform. Fast Fourier Transform (FFT) analysis determines the residual for the spectral display, K-factor, and individual harmonic measurements. Total Harmonic Distortion (THD) is determined by dividing the rms of the residual by the wide-band rms amplitude. With these techniques, harmonic measurement accuracy does not depend upon fundamental frequency. 51

and combine the signals from each channel. Combination measurements of power quantities include: ˆ Phase ˆ Active Power ˆ Reactive Power ˆ Apparent Power ˆ Power Factor ˆ Waveform Display The following sections provide instructions for performing measure- ments of parameters within this group. Connecting the Inputs When comparing two signals, configure the inputs of the Model 931A individually, as specified in earlier sections. See Section 3.2.2 to set up voltage connections and Section 3.2.3 for current connections. Make any comparison of voltage-to-voltage, voltage-to-current, or current-to-current in this manner. For phase angle and/or power quantity measurements, route the voltage signal to Channel 1, and the current signal to Channel 2. Since the voltage in a power system is usually more stable and less distorted than the current, the Model 931A uses Channel 1 as a reference for phase measurements. Both a voltage and current input signal are required to measure all power quantities. 3.6.1 Phase Angle Measurement The Model 931A can measure and display the phase angle between two AC signals routed to channels 1 and 2. A narrow-band quantity, phase is the difference between the two fundamental signal components. A signal at Channel 1 provides the reference to which the signal at Channel 2 is compared. For correct comparison, both signals must have the same fundamental frequency. 52

NOTE: See Section 3.2.2 and 3.2.3 for input connection description. Connect the signals to the appropriate input terminals and configure the measurement channel by pressing CHANNEL 1 SELECT and CHAN- NEL 2 SELECT. See channel selection screens below. 3.6.1.2 Performing the Measurement Press the PHASE/FREQUENCY key to produce a display similar to the one shown below: The large number at the top of the display shows the phase angle of the signal routed to Channel 2, relative to that of Channel 1. It also shows the frequency of the signal at Channel 1. Dashes will appear for phase angle if signals of sufficient amplitude are not routed to both Channel 1 and Channel 2. For a more detailed description of Frequency Measurement, see Sec- tion 3.5.4. 3.6.1.3 Phase Preference If the value displayed for Phase Angle does not appear correct, the phase preference may need changing. Choose either ±180◦ or 0−360◦. Also, set the phase to read negative or positive for Channel 2 lagging Channel 1. 53

none of the power quantities. Press the MENU key and select Phase Preference (Section 3.3.1.13) to set the phase preference. Table 3.8 describes the four possible phase settings and the resultant displays for each, when the signals, shown in Figure 3.13, are applied. See Section 3.6 for input connection description. Range Polarity Setting Resultant Setting for Ch 2 lagging Ch 1 Reading ±180◦ negative -60 ◦ ±180◦ positive +60 ◦ 0 − 360◦ negative 300◦ 0 − 360◦ positive 60◦ Table 3.8: Phase Convention Figure 3.13: Phase Angle Example 3.6.2 Active Power – Reactive Power The Model 931A can measure the active power (rms watts) and reactive power (vars) from the combination of an AC voltage routed to measure- ment Channel 1 and an AC current routed to Channel 2. NOTE: Refer to Section 3.6 for input connection description. 54

Configure the chosen measurement channels after connecting the voltage and current to the appropriate input terminals (see Figure 2.1 for instru- ment locations). Press CHANNEL 1 SELECT to begin configuring channel 1. The following menu will appear on the display: Arrows form the cursor, which highlights one of the selections. Press the arrow keys to locate the measurement value. For example, using the arrow keys move the cursor to “Van” to measure an AC voltage between inputs “A” and “N”. Press ENTER to confirm the selection. Press CHANNEL 2 SELECT to configure channel 2 current (e.g. Ia). Move the cursor to the desired measurement value and press ENTER to confirm the selection. For example, using the arrow keys move the cursor to “Ia” to measure an AC current at the “A” input terminals. 3.6.2.2 Performing the Measurement Pressing POWER/VARS will produce a display similar to the one shown below: The large number at the top of the display shows the active power measured. The lower number shows the reactive power. Also, the display indicates if the Model 931A is making wide-band or narrow-band measurements. 55

to 3.05 kHz) active power in Watts by taking the average of instantaneous values of voltage and current multiplied by each other. Wide-band reactive power (VARS) is determined by taking the vector difference of the product of the wide-band rms voltage and current (wide-band apparent power) less the active power. The formula is shown in 3.4 below: (3.4) ReactivePower = � (V A)2 − (ActivePower)2 The polarity of the wide-band reactive power is determined by the narrow-band result. Press SHIFT then NARROW-BAND to switch the measurement mode from wide-band to narrow-band. Narrow-band mode measures the fundamental magnitude of the voltage and current only, using proprietary DSP algorithms. Harmonics are ignored. Dashes will appear in the display if insufficient signals are present during measurements performed in narrow-band mode. Narrow band results are computed in 3.5 and 3.6. (3.5) ActivePower = Vfund × Ifund × cos(θ) (3.6) ReactivePower = Vfund × Ifund × sin(−θ) 3.6.3 Apparent Power – Power Factor The Model 931A can measure the apparent power (volt-amps, or VA) and power factor from the combination of an AC voltage routed to Channel 1 and an AC current routed to Channel 2. NOTE: See Section 3.6 for input connection description 3.6.3.1 Configuring the Channels Configure the chosen measurement channels after connecting the voltage and current to the appropriate input terminals (see Figure 2.1 for instru- ment locations). Press CHANNEL 1 SELECT to configure measurement channel 1 and to view the following menu: 56

the arrow keys to locate the measurement value. For example, using the arrow keys move the cursor to “Van” to measure an AC voltage between inputs “A” and “N”. Press ENTER to confirm selection. Press CHANNEL 2 SELECT to configure Channel 2 in the same way as for channel 1. An almost identical menu (except for In) will appear: Move the cursor to the desired measurement value and press ENTER to confirm the selection. For example, using the arrow keys move the cursor to “Ia” to measure an AC current at the “A” input terminals. 3.6.3.2 Performing the Measurement Press VA/PF to produce a display similar to the one shown below: The large number at the top of the display shows the apparent power measured. The lower number shows the power factor. Also, the display indicates whether the values are wide-band or narrow-band measurements. Press SHIFT then BAND-WIDE to change the measurement mode to wide-band RMS, including all frequencies up to 3.05 kHz. Wide-band apparent power is determined by multiplying the wide-band voltage and current as shown below. Power factor is the quotient of the Active Power divided by the Apparent Power as seen in 3.7 and 3.8. Wide-Band: (3.7) V A = Vrms × Irms (3.8) PF = ActivePower ÷ V A Press SHIFT then NARROW-BAND to change the measurement mode to measure the fundamental magnitude of the voltage and current only, using proprietary DSP algorithms. This measurement mode ignores 57

band apparent power is determined by multiplying the fundamental voltage by the fundamental current as seen in 3.9. Power Factor is the cosine of the angle between Vfund and Ifund as seen in 3.10. Narrow-Band: (3.9) V A = Vfund × Ifund (3.10) PF = Cos(θ) 3.6.4 Waveform Display Press the WAVEFORM key at any time to display waveforms for the signals at measurement channels 1 and 2. Initially, waveforms for both channels will be displayed. Display individual channels by pressing CHANNEL 1 SELECT or CHANNEL 2 SELECT. Press the WAVEFORM key again to display both wave shapes simultaneously. The Model 931A Waveform Display includes a text display showing the rms magnitudes for the two signals and the frequency of the signal at Channel 1. The following example shows a typical Waveform Display: Signals are aligned so that the zero crossings of each channel appear at the left-hand edge of the display. 3.7 Timer Measurements The Model 931A includes a timer for measuring events such as relay contact timing. The timer has two channels, which are optically isolated from the instrument common and from each other. Both inputs can accept various triggering inputs, including: ˆ Contact opening or closure, ˆ AC applied or removed (20 - 300 Vrms), ˆ DC applied or removed (4 - 300 Vdc). See Section 3.7.2.4, “Select Timer Trigger A” for more information. 58

The two timer inputs are labeled “A” and “B”, with one black terminal and one red terminal for each input. Apply AC or DC input signals to either channel without regard to polarity. NOTE: In contact closure or opening mode, external voltage should not be applied to the inputs; only DRY contacts should be used. 3.7.2 Configuring the Timer Press the CONFIG key to invoke the timer configuration menu, which will be similar in appearance to the following: Select timer functions using the arrow keys; highlight the desired item and press ENTER to confirm the selection. The following sections describe the individual selections from this menu. 3.7.2.1 Select Timer Function Select Function from the Timer Configuration menu and press ENTER to view the following display: ˆ “Time A to B” configures the timer circuitry to display the time elapsed between a valid trigger for the “A” input and a valid trigger for the “B” input. ˆ “Time A For X Counts” configures the timer to display the time elapsed between a valid trigger for the “A” input and the Xth valid trigger for the “A” input. ˆ “Time Width of A” sets the timer circuitry to measure the duration of the triggering event on the “A” input. 59

event at the “A” input. NOTE: The timer triggers without regard to polarity. If selecting DC Applied as the trigger and a symmetric signal of greater than 6 Vpp is applied, the rate displayed will be double the actual frequency. ˆ “Count A Events” configures the timer circuitry to display the number of valid trigger events, which occur on the “input”. These may be periodic or random. ˆ “Count A Gated By B” sets the timer circuitry to count events on input “A” only during the time in which a valid trigger condition exists on input “B”. The events counted during successive valid “B” input trigger periods are cumulative. 3.7.2.2 Timer Display Choices To select whether time data is displayed in seconds or in cycles, select Display Choice from the Timer CONFIG main menu and press ENTER. For cycles, the data may be based on 50 Hz, 60 Hz, or the fundamental frequency of the signal present at measurement Channel 1 (Ch 1 Hz). Select Display Choice from the Timer Configuration Menu to view the following display: ˆ Seconds sets the timer to display measurement results in seconds. ˆ Cycles (50 Hz) causes the timer to display the measurement result in cycles, assuming a frequency of 50 Hertz. ˆ Cycles (60 Hz) causes the timer to display the measurement result in cycles, assuming a frequency of 60 Hertz. ˆ Cycles (Ch 1 Hz) causes display of measurement results in cycles, using the signal present at Channel 1 as the reference frequency. 60

Select Hold Mode On Stop from the Timer Configuration Menu and press ENTER to view the following sub-menu: Use this sub-menu to leave the instrument in the measure hold mode at the end of a timer cycle. Select Disable to continue normal operation, with all measured param- eters being updated continuously. Select Enable to continue in the measure hold mode at the end of the timer cycle. It then retains values for all measured parameters as of the end of the timer cycle. 3.7.2.4 Select Timer Trigger A Select Trigger A from the Timer Configuration Menu and press ENTER to view the following display: This sub-menu allows selection of the type of input to be used for the trigger for timer “Channel A”. The following are descriptions of each of the choices: ˆ “DC Applied” configures the timer input to trigger with a ± 3 volts DC or greater signal. ˆ “DC Removed” configures the timer input to trigger with removal of a ± 3 volts DC or greater signal. ˆ “AC Applied” configures the timer input to trigger with an AC voltage. The minimum triggering voltage is frequency dependent, but must be greater than 3 volts rms at any frequency. Slight errors may occur, when using this mode of triggering, that depend on the 61

of frequency, is shown in the following graph: NOTE: The minimum rms voltage at 60 Hz is (approx.) 11 volts. ˆ “AC Removed” configures the timer to trigger on the removal of an ac voltage, as described above. The point in time at which the signal last falls below the threshold is interpreted as the trigger. Slight errors may occur, when using this mode of triggering, that depend on the instantaneous trigger voltage. However, this error should not exceed 1 millisecond. ˆ “Contact Open” configures the timer input to recognize the opening of an electrical contact as a trigger event. The threshold is (approx.) 2.9 volts, with a pull-up impedance of (approx.) 47 kilohm to a source voltage of (approx.) 8 volts. ˆ “Contact Closed configures the timer input to recognize the closing of an electrical contact as a trigger event. The threshold is (approx.) 2.6 volts, with a pull-up impedance of (approx.) 47 kilohm to a source voltage of (approx.) 8 volts. 3.7.2.5 Select Timer Trigger B Press the Timer CONFIG key and select Trigger B from the Timer Configuration Menu and press ENTER. Select the appropriate trigger signal type for timer “Channel B” from this menu. The choices for input “B” are exactly the same as those for input “A”. See Section 3.7.2.4. 3.7.3 Timer Measurement Categories All measurements performed by the timer section of the Model 931A can be classified as either time or count measurements. The following paragraphs describe both categories. 62

Stopped. Initially, the timer will be in Standby. After configuring the timer, press the ARM/RESET key to Arm the timer. A timing cycle begins with a start trigger, and the Timer switches from Armed to Active. When the predetermined stop trigger occurs, the timing cycle ceases, and the timer Stops (except in Count Modes, where it switches to Standby). The ARM/RESET key functions as a reset key, when the timer stops in time measurement modes, or at any time in count measurement modes. Press ARM/RESET to clear the timer data and reset the display to zero. Pressing ARM/RESET also switches the timer from the Stopped to Standby. The Model 931A displays the timer-state below the word “Timer.” A blank status indicator signifies the instrument is in Standby. 3.7.3.2 Time Measurements Time Measurement Timer functions return a time value with finite start and stop points. Measurements falling in this category are: ˆ Time A to B ˆ Time A for X Counts ˆ Time Width of A During these modes of operation, the timer cycles through all four timer states. 3.7.3.3 Count Measurements Count Measurement Timer functions result in measurements having a finite starting point, then are continuously updated. Measurements falling into this category are: ˆ Rate of A ˆ Count A Events ˆ Count A Gated by B In these modes of operation, the timer can only be in the Standby, Armed or Active states as described in Section 3.7.3.1. The Stopped State is invalid with these modes. 63

The Timer reports a time measurement after the timer stops (the Stopped State). The Model 931A then displays this value until pressing the ARM/RESET key (which returns the timer to the Standby state). During count measurements, the display continuously updates the count during the measurement cycle. Pressing the ARM/RESET key resets the count display back to zero, and also re-arms the timer. 3.8 Transducer Testing Testing transducers with the Model 931A is straightforward using an external source, such as a calibrator or source and load box. Also perform live, in-circuit tests. Prior to starting a transducer test the Model 931A automatically makes a self-calibration. Use the main measurement inputs to precisely monitor the transducer input values. Transducer output may be set to either Measured Quantity, Percent Full Scale, or Percent Error, while simultaneously displaying the transducer inputs. This provides a look at the input and output quantities for better control during the measurement, and fewer chances for measurement or setup errors. The Model 931A Transducer input uses accurate, optically isolated input sections to accept transducer outputs in the range of 0 − 10 Vdc or 0 − 100 mA. Alternatively, transducer custom pulse outputs may also be tested using the Model 931A Timer A input. 3.8.1 Configuring the Transducer Press SHIFT > CONFIG to configure transducer measurement section via a series of menus (a second function of TRANSDUCER). The main menu, in the series, is the Transducer Configuration menu, which is similar in appearance to the display shown below: The following paragraphs describe the functions and capabilities of each of the Transducer Configuration menu selections. 64

ENTER to view the following sub-menu: Select any of the available input modes for testing transducers from this menu. For 3-phase measurements, see description in Section 3.3.2.5. Menu selections are described below and help explain how these selections apply when performing Transducer Testing. ˆ “1Ph 2Wire 1E” sets the Model 931A to measure values in a single- phase circuit, having a hot wire and a neutral wire. Since sequential measurements are not necessary, the internal operating software for the Model 931A utilizes whichever inputs are currently routed to measurement channels 1 and 2. For a voltage or frequency transducer, use Channel 1 for the transducer input. For a current transducer, use Channel 2 for the transducer input, and route a voltage or current of the same frequency to Channel 1. Do not select the same input for both Channel 1 and Channel 2. See Figure 3.14. ˆ “1Ph 3Wire 2E” sets the Model 931A to measure values in a circuit having two hot wires and a neutral wire. Commonly referred to as Split-Phase, this type of circuit is generally used to supply residential service. This particular configuration is intended for testing 2-element transducers. See Figure 3.15. Use internal operating software definitions for inputs as follows: ”VanIa”, “VcnIc” (i.e., a sequential measurement of the following two combinations: voltage “A” to “N” with current “A”, and voltage “C” to “N” with current “C”). ˆ “3Ph 3Wire 2E” sets the Model 931A to measure values on a 3-phase delta circuit, for comparison with a 2-element transducer. Use internal operating software definitions for inputs as follows: “VabIa”, “VcbIc” (i.e., a sequential measurement of the following two combinations: voltage “A” to “B” with current “A”, and voltage “C” to “B” with current “C”). 65

3-phase delta circuit, for comparison with a 2.5-element transducer. See Figure 3.16. Use the internal operating software definitions for inputs as follows: “VanIa”; “VbIb”; and “VcnIc” (i.e., a sequential measurement of the following three combinations: voltage “A” to “N” with current “A”, voltage “b” with current “B”, and voltage “C” to “N” with current “C”). To create voltage “b”, connect the “B” voltage input to the “N” voltage input. ˆ “3Ph 4 Wire 3E” sets the Model 931A to measure values on a 3-phase Y circuit, for comparison to a 3-element transducer. See Figure 3.17. Use internal operating software definitions for inputs as follows: “VanIa”; “VbnIb”; and “VcnIc” (i.e., a sequential measurement of the following three combinations: voltage “A” to “N” with current “A”; voltage “B” to “N” with current “B”; and voltage “C” to “N” with current “C”). Three-phase display and percent error calculations use the average for V, A, θ (phase), and PF, and the total for W, VAR, and VA. 3.8.1.2 Input Type Select Input Type from the Transducer Configuration menu and press ENTER to view the following sub-menu: ˆ “Volts” sets the Model 931A to make Voltage measurements at the predefined input routed to Channel 1, for comparison to a voltage transducer. For 3-phase configurations, the display shows average voltage. See Section 3.2.2 for a description of AC voltage measurements. ˆ “Phase” sets the Model 931A to measure the Phase Angle between the voltage and current at the predefined inputs, for comparison to a phase angle transducer. For 3-phase configurations, the display shows average phase angle. See Section 3.6.1 for a description of phase measurements. 66

Based on voltage and current measurements from the predefined inputs, the results are compared to an active power transducer. For three-phase configurations, the display shows total active power. See Section 3.6.2 for a description of power measurements. ˆ “Volt-Amps” sets the Model 931A to calculate apparent power (VA). Based on voltage and current measurements from the pre- defined inputs, the results are compared to an apparent power transducer. For three-phase configurations, the display shows the total apparent power. See Section 3.6.3 for a description of apparent power measurements. ˆ “Amps” sets the Model 931A to make current measurements on the predefined input routed to Channel 2 and compares it to a current transducer. Route input to measurement Channels 1 and 2 if only a current signal is available. If available, route synchronous voltage signal to channel 1. For three-phase configurations, the display shows average current. See Section 3.2.3 for a description of AC current measurements. ˆ “Frequency” sets the Model 931A to measure frequency at (prede- fined) channel 1, for comparison to a frequency transducer. The displayed frequency actually represents the instantaneous value, which is updated with each measurement cycle. See Section 3.5.4 for a description of frequency measurements. ˆ “Vars” sets the Model 931A to calculate reactive power (vars) based on voltage, current, and phase measurements from the predefined inputs. The results are compared to a reactive power transducer. For three-phase configurations, the display shows the total reactive power. See Section 3.6.2 for a description of reactive power. ˆ “Power Factor” sets the Model 931A to calculate power factor based on voltage and current from the predefined inputs. The results are compared to a power factor transducer. For three- phase configurations, the display shows average power factor. See Section 3.6.3 for a description of power factor measurements. 3.8.1.3 Input Range Select Input Range from the Transducer Configuration menu and press the ENTER key to view the available input ranges. The displayed 67

Section 3.8.1.2 for a description of available Input Types). When the Model 931A is configured to test a voltage transducer, the display shows following selection menu: Custom allows the user to determine the upper and lower limits of the measurement range. Determine a custom range, as a part of this sub-menu, for all input types. See Section 3.3.3 for Data Entry Function description. 3.8.1.4 Output Range Select Output Range from the Transducer Configuration menu to view the following sub-menu: The Model 931A allows these output ranges when the transducer outputs are connected to the transducer terminals on the front panel. Within the ranges shown, the Model 931A accepts either voltage or current signals. Refer to Section 3.8 for details on connecting transducer inputs, and Section 3.3.3 for a description on data entry. ˆ Custom V allows the user to enter a voltage range within the limits of 0 to 10 volts DC. ˆ Custom mA allows the user to enter a current range within the limits of 0 to 100 milliamperes DC. ˆ Custom Pulse allows the user to setup the Model 931A to accept a calibrated pulse from the transducer that is proportional to the measured transducer value. 3.8.1.5 Display Input As Select Display Input As from the Transducer Configuration menu and press the ENTER key to view the following sub-menu: 68

measurement inputs in actual measurement units (e.g. volts, amps). ˆ “Percent Full Scale” displays the value present at the Model 931A measurement inputs as a percentage of full-scale. Full-scale is defined by the lower and the upper limit of the currently selected input range (see Section 3.8.1.3 for a description of Input Ranges). 3.8.1.6 Display Output As Select Display Output As from the Transducer Configuration menu to display the following sub-menu: ˆ “Measured Quantity” sets the Model 931A to display the actual value measured at the output of the transducer under test (i.e., volts or milliamperes). ˆ “Percent Full Scale” displays the measured value (at the output of the transducer under test) as a percentage of full-scale. Full-scale is defined by the lower and the upper limit of the selected output range. Does not apply for Custom Pulse. ˆ “Percent Error” displays the measured error of the transducer based on the measured input and output quantities. To properly utilize the Percent Error feature, enter the following: (1) the upper and lower transducer input quantities and (2) the upper and lower transducer output range limits. Setting the output range limits are critical for transducers having a lower output range limit of other than zero. For example a typical transducer may have a 4−20 mA output. With such a transducer, zero at the input corresponds to 4 mA at the output. 69

If needed, use the main measurement inputs on the Model 931A as the input for transducer tests at any value up to their rated maximum (see Specifications in Section 4). Connect the voltage and current measurement inputs according to the type of transducer being tested. The operating software defines which combination of inputs to use for testing of each type of transducer (except 1-Phase 2-Wire). These definitions are described in the Transducer Mode Selection menu, shown in Section 3.8.1.1. Figures 3.14 through 3.17 illustrate various examples of connections for transducer testing. Use any of the voltage and current inputs to measure single-phase, two- wire transducers since they do not require sequential measurements. Use channel 1 for voltage and channel 2 for current, as channel 1 is used as a reference channel, as the voltage signal is typically the most stable signal. 70

�������� ����������� ������������� ������� ���� ������ ������ � ���������� ���� ��� ���� �� �������� �������� � ��� � ���� ��� ���� �� �������� ������� ���� ��� ������ � ������ ��� ����� ���� ����� �������� Figure 3.14: 1-Phase, 2-Wire, 1-Element Transducer Test 71

CURRENT VOLTAGE TRANSDUCER SETUP 1 SETUP 2 SETUP 3 SETUP 4 SETUP 5 SETUP 6 NARROW-BAND-WIDE MEAS 3 PHASE CH1 RANGE RESTART CONFIG SHIFT HELP REVIEW PRINT LOG STORE SETUP SCALE ESCAPE ENTER VOLTS AMPS PHASE FREQUENCY POWER VARS VA PF HARMONICS WAVEFORM CHANNEL 1 SELECT CHANNEL 2 SELECT MEASURE HOLD CH2 RANGE MIN MAX TRANSDUCER MENU LOG DATA PRINT LAST SETUP CH1 / CH2 ON/OFF FUSE 1AF/250V 85-264 Vac 47-440 Hz 110-250 Vdc RS-232 GROUND BEFORE USE A B C N 750 Vrms / 1000 Vdc MAX 20 Arms MAX 10Vdc MAX 100mAdc MAX A B C DISPLAY CONFIG ARM / RESET A B 300V MAX L1 L2 L1 L2 N N Iout LOAD SOURCE { + - { I1 + - { I2 + - { V1 + - { V2 + - Figure 3.15: 1-Phase, 3-Wire, 2-Element Transducer Test 72

CURRENT VOLTAGE TRANSDUCER SETUP 1 SETUP 2 SETUP 3 SETUP 4 SETUP 5 SETUP 6 NARROW-BAND-WIDE MEAS 3 PHASE CH1 RANGE RESTART CONFIG SHIFT HELP REVIEW PRINT LOG STORE SETUP SCALE ESCAPE ENTER VOLTS AMPS PHASE FREQUENCY POWER VARS VA PF HARMONICS WAVEFORM CHANNEL 1 SELECT CHANNEL 2 SELECT MEASURE HOLD CH2 RANGE MIN MAX TRANSDUCER MENU LOG DATA PRINT LAST SETUP CH1 / CH2 ON/OFF FUSE 1AF/250V 85-264 Vac 47-440 Hz 110-250 Vdc RS-232 GROUND BEFORE USE A B C N 750 Vrms / 1000 Vdc MAX 20 Arms MAX 10Vdc MAX 100mAdc MAX A B C A N C C A N B B DISPLAY CONFIG ARM / RESET A B 300V MAX Iout LOAD SOURCE { + - { I1 + - { V1 + - { V3 + - { I2 + - { I3 + - NOTES: In 3-Phase 4-Wire 2.5 Element Mode, the Model 931A voltage input 'B' must be connected to voltage input 'N'. Figure 3.16: 3-Phase, 4-Wire, 2.5-Element Transducer Test 73

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Figures 3.14 through 3.17 illustrate the Transducer Signal Outputs con- nected between the transducer current input (far right) and common (middle). If testing transducers with voltage outputs, connect them between the transducer voltage input (left) and common (middle). NOTE: Be certain to configure the Model 931A to accept the type of transducer signal and range, whether voltage or current output. Sec- tion 3.8.1.4 describes available Output Ranges. 3.8.4 Performing the Measurement Once in the Transducer Configuration Menu, press the ESCAPE key to automatically place the unit in the transducer measurement mode. To access the Transducer Configuration Menu, press SHIFT then CONFIG. Instrument configuration determines the appearance of the display during transducer measurements. The upper number represents the transducer input, and the lower number represents the transducer output. Display configuration determines whether measurement results are pre- sented as a measured value, or as a percent of full-scale. Sections 3.8.1.5 and 3.8.1.6 describe the Display Modes. Additionally, the Model 931A can present the lower number as a percentage of error in the transducer. Percentage error is determined by comparing the ratio of the input and output values to the ratio of the input and output ranges. Section 3.8.1.6 describes how to set the Model 931A to display percentage error in transducer measurements. 3.8.5 Custom Pulse, or Contact Output Tests 3.8.5.1 Choosing a Test Method Testing transducers with contact outputs can be accomplished by using the Custom Pulse feature of the Model 931A. By following the steps outlined below, most transducers with contact outputs may be tested simply and accurately. 1. Determine the type of transducer output. 2. Configure the Transducer menu, on the Model 931A. 3. Configure the Timer menu, on the Model 931A. 4. Setup the required test equipment and transducer. 5. Test the transducer. 75

Most transducers with contact (or pulse) outputs use either an electrome- chanical or a solid-state relay. If the transducer has an electromechanical relay at the output, it is important to use the Debounce feature on the Model 931A. Otherwise, do not use it. 3.8.5.3 Configuring in the Transducer Menu Press SHIFT then CONFIG to access the Transducer Configuration menu. Set each of the six categories in the Transducer Configuration menu that best fits the transducer being tested. Use the arrow keys and ENTER to make and confirm selections. As each of the six categories is setup, the arrow cursor moves down to the next category. The sample menu shown below pertains to a 3-phase power transducer illustrated in Figure 3.18. Make these selections as follows (as shown in the screen above). 1. Input Mode – select the Phase, number of Wires and Elements (e.g. 3P 4W 3E). 2. Input Type – select Volts, Phase, Power, Volt-Amps, Amps, Frequency, Vars, or Power Factor (e.g. Power). 3. Input Range – select the transducer range being tested (e.g. 0 - 1500). 4. Output Range – this selects the Custom Pulse feature. Choose Custom Pulse (only) for this menu item. Note that after Custom Pulse is selected (under the Transducer Output menu) the bottom line will clear and read ”Watt-hours per pulse = 0.00000”. Use the right and left arrows to move the cursor and the up and down arrows to change the digit value. 100 (watt hours per pulse) is the largest acceptable value 5. Display Input As – select either Measured Quantity or Percent Full Scale (e.g. the above settings will display Measured Quantity in kWatts). 76

Error. Although the menu choices include Percent Full Scale, only Measured Quantity and Percent Error pertain to Custom Pulse. The sample Transducer Configuration Menu shown below illustrates settings for a different transducer using the “Rate of A” Function instead of “Time A to X Counts.” Notice the large difference in Output Range compared to the “Time A to X Counts” configuration above. When all of the six categories are set up correctly, press ESCAPE to return to the main menu. If initially setting up a transducer custom pulse test, proceed to the section on Timer Configuration below. 3.8.5.4 Configuring in the Timer Menu Press the Timer CONFIG key to access the Timer Menu. A sample menu is shown below. Only two selections under Timer Function apply to the Custom Pulse feature: “Time A For X Counts” and “Rate of A.” Make the Timer Configuration selections as follows: 1. Function – select either Time A For X Counts, or Rate Of A. Use Time A for X counts if the contact closure rate is < 1/sec. Use Rate of A if the contact closure rate is > 1/sec. For more details on which function to choose, see below under “Contact Closures < 1/second”, or “Contact Closures > 1/second.” 77

X awaiting confirmation. Use the Up or Down arrow keys to change this value. 3. Display choice – select Seconds 4. Hold Mode On Stop – select Disable 5. Trigger A – select Contact Closed or Contact Open 6. Trigger B – do not use this item for the Custom Pulse function. 7. Debounce A – select “ON” for electromechanical contacts, “OFF” for solid-state contacts. 8. Debounce B – do not use this item for the Custom Pulse function. 3.8.5.5 Contact Closures < 1/second The best selection for contact closures < 1/second is Time A For X Counts. This function allows the Model 931A to measure transducers with contact outputs that are relatively slow – in the range of seconds between pulses. Typical devices that fit into this category could be transducers. 1. Select Function, in the Timer Configuration Menu, and press ENTER. 2. Select Time A For X Counts in the Select Timer Function menu, using the arrow keys and press ENTER. 3. When ENTER is pressed, a numerical value replaces X and awaits adjustment or confirmation. 4. Use the UP or Down arrow keys to increase or decrease the number of contacts. 5. Press ENTER to confirm the selection and return to the Timer Configuration menu. 78

Counts” function, the Model 931A computes average output values, or the % error. It does this by measuring the overall time for multiple contacts (defined by X) and divides that time by the number of contact closures. At the end of a test, the Model 931A displays and holds the Input and Output values until pressing ARM/RESET, which begins a new test. 3.8.5.6 Contact Closures > 1/second “Rate of A” is generally used for calibration standards (transducers) with output rates normally much greater than 1 Hz. Notice the values listed in the Timer Configuration Menu. Remember that Trigger B and Debounce B are not used in Custom Pulse transducer measurement functions. 1. Press the Timer CONFIG key to access the Timer Configuration Menu. With the cursor, select “Function” and press ENTER to access the Timer Function menu. 2. In the Timer Function menu select “Rate of A” and press ENTER. 3. The ”Rate of A” Function also continuously updates the transducer measurements during a test. In this example, “Rate of A” was chosen based on the nameplate rating of 0.00001 Whr/pulse. Dividing the number of Transducer Input Watts by 0.00001 Whr/pulse and dividing by 3600 sec/hour gives a pulse rate of approximately 20,000 pulses per second. The calculation is shown in 3.11 below. (3.11) (718.8W ÷ 0.00001Whr/pulse) ÷ 3600sec/hr = 19, 966pulses/sec 79

terminals with suitable cables. The Custom Pulse function works only with Timer Input A. Connect the transducer and the Model 931A to a source providing the required output levels for testing the transducer. Refer to Figure 3.18 for an illustration of using a power transducer. Note: Check the Model 931A maximum ratings prior to applying power, to avoid damaging the equipment. Always consult the manufacturers original documentation for the power source and the transducer for proper test setup. This may be a manual, or simply be the nameplate on the transducer. 3.8.6 Performing a Test 3.8.6.1 For Contact Closures < 1/second Use Time A For X Counts. After setting up the test and configuring the Model 931A, apply the input power source to the transducer and Model 931A. Refer to Figure 3.18. Press the TRANSDUCER key to view the standard measurement screen. Initially, the Model 931A display will appear similar to the screen below. 1. Allow a few seconds for the Transducer Input value to stabilize. 2. Press the ARM/RESET key twice to reset and arm the timer function. For X = 1, the first pulse starts the timer and the next pulse concludes the timing interval. If using multiple counts per measurement (X > 1), the timer will begin counting on the first pulse and stop with the last pulse. 3. During the custom pulse test the OUTPUT value will change to dashes, as shown below and the date (in the lower right) will be replaced with a timer value, incrementing in seconds. 80

replace the dashes, and the timer value will freeze, indicating the transducer input, transducer output and the number of seconds. The Model 931A will be placed in Hold Mode. 5. To repeat the test with the same or different transducer input, press the ARM/RESET key, adjust the source as necessary, allow the transducer input display to stabilize and press the ARM/RESET key again. 6. To configure new test parameters, press either SHIFT then CON- FIG (transducer) or CONFIG (timer) to change the measurement settings. After re-configuring the test parameters, press the TRANS- DUCER key and the Model 931A is ready for another test. To start the next test, press the ARM/RESET key twice. 3.8.6.2 For Contact Closures > 1/second After setting up the test and configuring the Model 931A, apply the input power source to the transducer and Model 931A. Refer to Figure 3.18. 1. Press the TRANSDUCER key to view the standard measurement screen. Press the ARM/RESET key again if the display is not indicating a reasonable output value, as illustrated below. 81

corner of the display) press the ARM/RESET key. It should immediately begin measuring the transducer. Also, the Timer information (including the contact or pulse output rate in Hertz) should appear and replace the date and time information. The screen below illustrates the Model 931A measuring a transducer using “Rate of A.” 3. Using the “Rate of A” Function, the Model 931A should continually update the measurement values. The Model 931A also cycles between each measured phase indicated in the lower left corner of the display. 4. The Transducer Input value indicates the total input, in this case three-phase power. 5. Adjust the source for subsequent tests to be performed. 82

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Use an external current transformer (CT) and potential transformer (PT) to extend the measurement range of the Model 931A. If used, however, do not exceed the input range of the instrument (refer to Chapter 4, Specifica- tions). Using an external PT and/or CT by directly displaying measured primary CT and PT values greatly simplifies measurement. Programming the scaling feature of the Model 931A, whether for magnitude or phase, effectively cancels offset errors. To activate and configure the scaling function, press SHIFT then SCALE. See Section 3.3.2.17 for details on using the Scale feature. Measure the ratio and phase error of a CT or a PT by using the CH1/CH2 function included in the Model 931A. Press the CH1/CH2 key to display the phase difference and magnitude ratio of the signals measured by Channel 1 to the signal measured by Channel 2. Further discussion of the CH1/CH2 function can be found in Section 3.3.1.17. Example: measure the ratio of a PT by performing the following steps: 1. Use Channel 1 to configure the Model 931A to measure the voltage at the input of the PT. 2. Use Channel 2 to configure the Model 931A to measure the output of the PT. 3. Apply the operating voltage to the input of the PT, and press the CH1/CH2 key. 4. The resultant display shows the voltage at Channel 1 divided by the voltage at Channel 2, along with the phase angle between the two. 3.10 Data Logging The Model 931A data-logging feature greatly simplifies recording measure- ments, either from the front panel or through the serial interface for later review. The following paragraphs describe how to record and review data. 3.10.1 Capturing Data Use the LOG DATA function to record four different data type measure- ment results in internal memory. These data types are: ˆ Standard data includes all of the Narrow-Band and Wide-Band parameters for Channels 1 and 2, along with Timer and Transducer results. All logged data is tagged with the time and date. This type 84