Keithley 148 Instruction Manual

detects Kelthley~in&&nts, Inc. ~&arrantSth~s product to befree from defects fin metertal~ Andy workmanship~ for~e~period of 1 year from date of ship- fin metertal~ Andy workmanship~ for~e~period of 1 year from date of ship- ~~ menb During.the warranty period;~~tia~@;~at our option, either repair ~~ menb During.the warranty period;~~tia~~ill;~at our option, either repair ,~~ ,~~ ~. or ~replatie any~ product that proves~to be defective; :~ ~. or ~replatie any~ product that proves~to be defective; :~ ~~ To~exercise this warranty, ~write~or $811 ~your lo&Kehhley~mpreesnt-: ~~ To~exercise this warranty, ~write~or $811 ~your l6&Keithiey~~p~epresent-: ative, ,or contacts Keithley headquarters in Cleveland, ohlti.~You~will~be ative, ,or contacts Keithley headquarters in Cleveland, ohlti.~You~will~be given prompt assistance and return instructions, Send:the instrument; given prompt assistance and return instructions, Send:the instrument; ~‘~ transportation prepaid; to the indir+sd service f&lii~ jIegairs @l be ~‘~ transportation prepaid; to the indir+sd service f&lii~ jIegairs @l be ~~ ~~ ~rnade~ land the~~instrument returned,~ transpotitiort prepeid.~ R~epaired ~rnade~ land the~~instrument returned,~ transpotitiort prepeid.~ R~epaired products~are~vyarrsnted fork the:bMance of the origin8~warianty period, products~are~vyarrsnted fork the:bMance of the origin8~warianty period, ~~ ~~ or at least 90 ~days. or at least 90 ~days. : LIMITATION~~OF~WARAANTV~~ : LIMITATION~~OF~WARAANTV~~ This warranty does not epply~to ~defectsresulting~ from unauthorized This warranty does not epply~to ~defectsresulting~ from unauthorized mpdification or misuse oft any product or part. This warmnty al&o does mpdification or misuse oft any product or part. This warmnty al&o does ~~ not spply to~fuses; batter@, or damage from ~battery leakege~~ ~~ ~~ not spply to~fuses; batter@, or damage from ~battery leakege~~ ~~ This werranty is in lieu,of all other &rranties, expra$ed or implied, in- This werranty is in lieu,of all other &rranties, expra$ed or implied, in- dluding~ any implied ~warranty of :merchentability nor f%ne& -for a par; dluding~ any implied ~warranty of :merchentability nor f%ne& -for a par; ticularuse; Keithley Instruments, ~lnti. shall not bs IiabMfor any indirect, ticularuse; Keithley Instruments, ~lnti. shall not bs IiabMfor any indirect, special nor coosequential~damsges. ~~~ ~~~~ special nor coosequential~damsges. ~~~ ~~~~ ~~~ ~~ ~~~ ~~ ~~ ~~ ~~ ~~ ;’ ~~~ ;S~~~EM~E,N~T~OF~CAL1BRATION Ran ~: : ~~ ;’ ~~~ ;S~~~EM~E,N~T~OF~CAL1BRATION Ran ~: : ~~ .~ ~~ ~~~ .~ ~~ ~~~ ~~~ This ~itiStrument~ has, been~ inspected land t&tedin~ crCcOrdance v&h ~~~ This ~itiStrument~ has, been~ inspected land t&tedin~ crCcOrdance v&h specifications bublishedby Keithley instruments, fin& ~~ specifications bublishedby Keithley Instruments, fin& ~~ : The~at%uracy and calibration~of this instrument am traceable to the ~~ : The~at%uracy and calibration~of this instrument am traceable to the ~~ ~Nationat ~Bureau of Standards through equipment which is cal~@reted at ~Nationat ~Bureau of Standards through equipment which is cal~@reted at ,~ fWrned ~Jnterv& by comparisqn to ,~ertlfii Standards maintained in ,~ @anned ~Jntery&ls~ by comparisqti !a ,~et$fii standafds nMin@nad in the Laboratories of :Keithley lnstruments;~ Inc. the Laboratories of :Keithley Instruments;~ Inc.

DOCUMENT #29029

(S102) ................. 44 31 Resistor LOcationS on RANOE SWitCh (5102) ................. 44 0375

conveniently measures dc potentials from 10 nanovolts (10 x 10-g volts) to 100 millivolts full scale. It makes accurate and sensitive measurements without painstaking methods often previously required. Meter accuracy is 2% of full scale on all ranges. Noise is less than 1 nanovolt peak-to-peak on the lo-nanovolt range. Zero drift is less than 10 nanovolts per 24 hours after warm-up. On the three most sensitive ranges, line-frequency rejection is greater than 1OOO:l. b. For reliable and versatile use, the Nanovoltmeter is of solid-state design, except for the first two input stages. It has high line isolation and battery or line operation. FIGURE la. Front panel. 0972

eliminat- ing many grounding problems. Battery operation also allows flexibility and convenience in use. The Model 148 automatically recharges the battery if needed when the ac power cord is connected. b. The Nanovoltmeter has a 21 volt at 1 milliampere output at full-scale meter deflections for driving a recorder or oscilloscope. Accuracy is 1% of full scale for output. c. A zero suppression circuit permits measuring small changes in a larger dc signal. l-3. APPLICATIONS. a. The Model 148 Nanovoltmeter measures very small dc potentials or small changes in dc potentials from low impedance sources. These are found in fundamental or applied research, laboratory standards work, cryogenic experiments and instrument development for space research. It can also serve as an amplifier in these uses. b. Typics.1 uses include measuring small temperature differences and small temperature changes indicated by thermocouple outputs, small changes in conductance, super conductivity in the lo-6 ohm range, and thermopile outputs used in narrowband spectrum analysis. Other uses are determining the thermoelectric power of metals, conducting Hall effect studies, and making Bolometer measurements. Also, the Model 148 is suited for use with potentiometers, ratio sets and resistance bridges, including Wenner, Wheatst and Kelvin Double bridges. It can be used to make 4-terminal resistance measurements. 2 0972

GENERAL DESCRIPTION MODEL 148 ZERO s”PPmssIoN POWER SWITCH * 5201 COARSE 5103 FINE R168 4 FIGURE 2. Front Panel Controls. 0972

SECTION 2. OPERATION OPERATION .2-l. FRONT PANEL CONTROLS. (See Figure 2.) a. AC CONNECTED Lamp. The Lamp is lit whenever the unit is connected to the ac line and the POWER SUPPLY Switch is in the AC or OFF position. NOTE The AC CONNECTED Lamp indicates only that the instrument is connected to the ac power line; it does not indicate that the Nanovoltmeter is operating. Also, when the POWER SUPPLY Switch is turned from AC to OFF, a difference in Lamp brightness is normal. b. BATTERY CHARGING Lamp. When lit, this Lamp indicates the battery is charging. The charge current determines its brightness. If the lamp is not lit, then the battery is charged. c. POWER SUPPLY Switch. The Switch controls the mode of operation for the power supply. 1. AC position: The Nanovoltmeter will operate from the ac power lint. The battery will be charged if needed; then, the BATTERY CHARGING Lamp will light. 2. OFF position: The Model 148 is not operating. However ) tk! battery will be charged, if needed and if the power cord is connected. 3. BATTERY position: The Nanovoltmeter is operated from its battery. The ac power line is internally disconnected; the AC CONNECTED Lamp is off; the battery cannot be charged. 4. BATT.TEST position: When the POWER SUPPLY Switch is held in this position, the Model 148 shows the state of the battery charge directly on its meter. All circuits within the instrument are the same as for battery operation except at the meter terminals. Switch Settin TABLE 1. Indicating Lamps and POWER SUPPLY Switch Settings. The table shows the relationship between the front panel lamps, the power cord and the POWER SUPPLY Switch setting.

d. RANGE Switch. The RANGE Switch selects the full-scale meter sensitivity (either microvolts or millivolts) for one of nine ranges, from 0.01 to 100. e. FUNCTION Switch. The FUNCTION Switch selects the function - MICROVOLTS or MILLIVOLTS - which is to be measured. f. ZERO SUPPRESS Controls. Two controls determine the amount of zero suppression. 1. The COARSE Control disconnects the suppression circuit (in OFF position) or selects one of four suppression voltages in decade steps. Refer to Table 3. 2. The FINE Control is a continuously variable adjustment for the suppression voltage set by the COARSE Control. It adjusts the range between the positive and negative values of the maximum voltage set by the COARSE Control. g. INPUT Receptacle. The INPUT Receptacle is of a special low-thermal design. Use only the Models 1481, 1482 and 1486 for mating connectors. WER 5103: RD FIGURE 3. Model 148 Rear Panel Controls and Connections. Circuit designations refer to Replaceable Parts List and schematic diagrams. 2-2. REAR PANEL CONTROLS AND CONNECTIONS. a. Line Voltage Switch. The screwdriver-operated slide switch sets the Model 148 for 117 or 234~volt ac power lines. b. Fuse. 1. For 117~volt operation, use a 3 AG or MDL Slow-Blow l/8-ampere fuse. 2. For 234volt operation, use only a MDL Slow-Blow l/16-ampere fuse. c. Power Cord. The 3-wire power cord with the NEMA approved 3-prong plug provides a ground connection for the cabinet. An adapter for operation from 2-terminal outlets is provided. 6 0464

OPERATION A note above the power cord shows the ac power line frequency for which the rejection filter is adjusted. The instrument will work at any line frequency from 50 to 1000 cps, but ac rejection is best at the indicated frequency. d. DEMODULATOR TEST. A phone jack provides access to the demodulator for test purposes. e. OUTPUT. The OUTPUT Receptacle provides fl volt at one milliampere for a full-scale meter deflection on any range. f. GND and LO Terminals. The ground terminal (GND) is connected to the chassis and the third wire of the power cord. The low terminal is connected to circuit ground and the low side of the input connection. 2-3. MODE OF OPERATION. The Model 148 operates either from an ac power line or from its battery. For most uses, it functions well from ac. Use battery operation, however, if the ac power line will create ground loop or isolation problems. Isolation from low to ground is complete for battery operation when the power cord is disconnected; it is greater than 10' ohms with the power cord connected. Also use battery operation to reduce the 8-cps ripple which may appear at the output with the input shorted in ac operation. See paragraph Z-13. NOTE Before using the battery operation, thoroughly read paragraph 2-4. Inproper battery operation can damage the battery pack and lead to inaccurate measurements. 2-4. BATTERY OPERATION. a. The Model 148 is supplied w;th a rechargeable 6-volt, 4 ampere-hour nickel-cadmium battery pack. Re<,c~mmended: Do not use the battery more than eight consecutive hours without recharging. At this discharge rate / the battery should last about 1000 recharge cycles. NOTE Permanent damage to the battery pack occurs if it is used for more than 14 consecutive hours without recharging. At this discharge rate, the recharge cycles are greatly reduced. Before using the Model 148, check the state of the battery charge. b. Check the battery charge before making a measurement. Hold the POWER SUPPLY Switch in the BATT. TEST position. The minimum acceptable charge is a meter indication of +8; full charge is shown by the BATTERY CHARGING Lamp not being lit. Recharge if needed. Otherwise, battery operation is the same as for the ac power line operating mode; refer to paragraph 2-5. 1067' 7

NOTE When the battery is used beyond its capacity, two effects are seen. There is a shift in zero offset from ac to battery operation. Also, the power supplies do not reg- ulate and high ripple voltages appear at the supply outputs. (See paragraph 4-7.) c. To recharge the battery, come-t the power cord to an ac power line. Turn the POWER SUPPLY Switch to AC or OFF. The BATTERY CHARGING lamp will light. The battery will be charged only if needed, and the circuit automatically prevents it from being overcharged. d. It is suggested that the battery be used during the day and be recharged at night. Leave the instrument always connected to the ac power line; then turn the POWER SUPPLY Switch to OFF at night, After a fully charged battery is used for eight consecutive hours, it will recharge within 14 hours. Leaving the power cord connected has little effect on the isolation: 109 ohms with the POWER SUPPLY Switch in BATTERY position and the low-ground link disconnected. 2-5. OPERATING PROCEDURES, a. Set the front panel controls as follows: POWER SUPPLY Switch OFF FUNCTION Switch MILLIVOLTS RANGE Switch 100 ZERO SUPPRESS COARSE Control OFF NOTE Make sure the ZERO SUPPRESS COARSE Control is OFF. If it is not, a suppression voltage is introduced, causing an error in measurements. b. Connect the unknown voltage source to the INPUT Receptacle. Refer to paragraph 2-6 for suggestions. c. Check the voltage shown on the rear panel Line Voltage Switch; connect the Model 148 to the ac power line. Make sure the frequency shown above the power cord is the frequency of the ac power line. At this point, the AC CONNECTED Lamp will light, as will the BATTERY CHARGING Lamp if the battery is being charged. If the circuit low is to be at ground, put the low-ground link between the LO and GND terminals on the rear panel. d. Turn the POWER SUPPLY Switch to the desired mode of operation, AC or BATTERY. e. Increase the sensitivity of the Model 148 until the meter shows the greatest on-scale deflection. 1. Check the source resistance to make sure it is within the maximum value specified for the range being used. (See Table 2.) If the maximum resistance is exceeded, the Model 148 may not be within its specifications. 1067

OPERATION 2. Zero offsets with the Zero Suppress Controls off will vary with the quality of the circuit's thermal construction. See paragraph 2-14. when a Model 1486 with a copper-wire short is on the Model 148 INPUT Receptacle, offset should be less than 0.2 microvolt. 3. Shifts in source resistance also affect the zero offset, if the source resistance approaches the maximum value given in Table 2. This effect is negligible for source resistances less than 10% of the maxiwm value. 4. If the input is left completely open-circuit, the meter will drift off scale on any range. 5. Refer to Table 4 if problems exist during the measurement. Minimum Input Resistance Maximum Source Line Frequent Range Greater Than Resistance Rejection 0.01 microvolt 1 kcl 10 n 3OOO:l 0.03 microvolt 3 kcl 30 n 1OOO:l 0.1 microvolt 10 kn 100 n 1OOO:l 0.3 microvolt 30 kn 300 11 5OO:l 1 microvolt 100 lcrl 1 lu? 5OO:l 3 microvolts 300 kn 3 kc1 1OO:l .O microvolts 300 kll 3 kn decreasing i0 microvolts 300 kn 3&l to 10 microvolts 300 krl 3kn 5O:l 0.01 millivolt 1 I%,2 10 kn 100: 1 0.03 millivolt 1lQ 10 kcl 5O:l 0.1 millivolt l?Sl 10 kn 2O:l 0.3 millivolt 1 Ma. 10 kn 2O:l 1 millivolt 1Kl 10 kn 2O:l 3 millivolts 3Kl 30 m 1O:l .O millivolts 5 Ml 50 Icn 1O:l IO millivolts 5 I%1 50 k!J 5:l 10 millivolts 5 Nl 50 kn 5:l TABLE 2. Model 148 Input Resistance, Maximum Source Resistance, and Minimum Line Frequency Rejection by Range. The rejection is the ratio of impressed peak-to-peak line frequency (50 or 60 cps) voltage at input to the indicated dc voltage. f. Three millivolt and microvolt ranges overlap: 0.01, 0.03 and 0.1 millivolts and 10, 30 and 100 microvolts. use the millivolt ranges when the source resistance is high or if large 60-cps fields are present. The micro- volt ranges are more convenient to use if subsequent measurements require more sensitive ranges. Refer to Table 2 for maximum source resistance and line frequency rejection by range. g. At low levels, spurious emf's may be generated simply by contact between the input leads and the circuit under test. If possible, always leave the instrument connected, and adjust the zero after establishing a zero reference in the apparatus under test. For example, in bridge measurements, 1067 9

disconnect the bridge exciting voltage; or with a phototube, shield the tube from light. 2-6. ACCESSORIES FOR INPUT CONNECTIONS. a. The easiest way to connect the voltage source to the Model 148 input is with the Model 1481 Low-Thermal Input Cable supplied with the instru- ment. Use the Cable for temporary setups, for measurements at several points, and when fast connections are needed. The Model 1481 connects directly to the INPUT Receptacle. I FIGURF: 4. Model 1481 Low-Thermal b. Where more permanent setups are Input Cable. possible or where very low thermal connections are needed, use the Model 1482 Low-Thermal Input Cable. It is similar to the Model 1481, except it has bare copper leads instead of alligator clips. Clean the bare wire with a non-metallic abrasive, such as Scotch Brite or its equivalent, before making the connection. Crimp connections to the voltage source, as possible with the Model 1483 Kit, provide the best low-thermal connections. C. If cadmium solder is used for a connection, make sure the soldering iron used is clean and that it has not been used with regular solder before. Use only rosin solder flux. If possible, heat sink all cadmium-soldered joints together to reduce generated thermal emf's. d. Use crimp connections with copper wire and lugs for the best low-thermal joints. The Model 1483 Low-Thermal Connection Kit contains a crimp tool, shielded cable, an assortment of copper lugs, copper wire, cadmium solder and nylon bolts and nuts. It is a complete kit for making very low-thermal measur- ing circuits. The Kit enables the user of the Model 148 to maintain the high thermal stability of the Nanovoltmeter in his own circuit. 'IGURE 5. Model 1483 Low-Thermal Connection Kit. e. The Model 1486 male low-thermal input connector is for connecting custom- made circuits to the Model 148. It also makes a good low-thermal shorting plug for testing the Nanovoltmeter: crimp a short length of pure copper No. 18 or No. 20 wire between the two pins of the connector. f. Other available accessories are: The Model 1484 Refill Kit, which contains replacement parts for the Model 1483. The Model 1485 female low- thermal input connector to use with the Model 1481, 1482 or 1486 for building shielded low-thermal circuits. 10 0464.

OPERATION 2-7. ZERO SUPPRESS OPERATION. a. Purpose: The zero suppression circuit cancels any constant voltage in order to use a more sensitive range to observe a superimposed signal. up to 100 times full scale may be suppressed on the ranges from 0.1 millivolt to 0.01 microvolt. For example, the Model 148 can measure changes of less than one microvolt in a lOO-microvolt steady signal on its l-microvolt range. b. Suupression Voltaxes Available: The COARSE Control sets the suppression voltage to one of eight values, depending upon its setting and the FUNCTION Switch setting. (Refer to Table 3.) The FINE Control continuously adjusts the voltage between tile positive and negative value of COARSE Control setting. For example, if the COARSE Control is at 1 for a suppression voltage of 0.24 millivolt, the FINE Control adjustment span is from -0.24 mv to 0 to +0.24 mv. FUNCTION Switch Setting MICROVOLTS MICROVOLTS MICROVOLTS MICROVOLTS ZERO SUPPRESS COARSE Control Setting 1 2 3 4 Maximum Suppression Voltage 0.24 microvolt 1.2 microvolt6 12 microvolt6 120 microvolt6 MILLIVOLTS 1 0.24 millivolt MILLIVOLTS 2 1.2 millivolts MILLIVOLTS 3 12 millivolts MILLIVOLTS 4 120 millivolts TABLE 3. Suppression Voltage by Control Settings. The zero suppression voltage shown is the maximum value, ?15%, for each FUNCTION Switch and COARSE Control setting. c. Operation, 1. Keep the COARSE Control in OFF position. Adjust the RANGE and FUNCTION Switches for the most sensitive meter reading. 2. Completely turn the FINE Control in the direction opposite to the meter deflection (counterclockwise for positive deflections and clockwise for negative deflections). 3. Increase the COARSE Control setting until the meter needle passes through zero. Adjust the FINE Control for zero deflection. 4. Set the RANGE Switch to a more sensitive range, up to 100 times more sensitive than the original range (four RANGE Switch positions). Readjust the FINE Control to zero, if necessary. 0365 11

NOTE On the highest zero suppression range - 120 millivolts maximum - a zero offset will be apparent when changing the RANGE Switch settings. On this zero suppres- sion range, first set the RANGE Switch to the range intended to be used. Then zero the meter with the ZERO SUPPRESS FINE Control. This offset is introduced only when the ZERO SUPPRESS COARSE Control is set to 4 and the FUNCTION Switch is set to MILLIVOLTS. There is no significant offset on any other zero supprss- sion range. 2-8. DIFFERENTIAL MEASUREMENTS. a. The Model 148 will measure the difference between two voltages, neither or which is at power line ground. It can be floated up to 1-400 volts off ground in ac operatior When the Model 148 is battery operated it is completely isolated from line. Unplug the Model 148 power co? and use battery operation before measuring a source which is more than f400 volts instantaneous off ground. Damage to the instrument can result if the power line is connected under these conditions. CAUTION The front panel controls are electrically connected to the case. If the power "cord is unplugged, the case may be at a voltage equal to the off-ground voltage. Use necessary safety precautions. - b. For best results in making differential measurements, follow the steps below: 1. Remove the link from the LO or GND terminal on the rear panel. 2. Connect the voltage source to the Nanovoltmeter i,L,wt. Make measurements as de- scribed in paragraph 2-5. The zero suppress controls may be used for differential meas- urements. Do not ground any recorders used with this operation, since the low of the Model 148 output is no longer grounded. 3. If power line frequency pickup is a problem, battery operation usually provides better results. 2-9. RECORDER OUTPUT. The output of the Nanovoltmeter for a full-scale meter deflection on any range is *l volt at one milliampere. Accuracy is 1% of full scale. Output resis- tance is less than 5 ohms within the amplifier pass band. Output may be used during both ac and battery operation. If the Model 148 is used for differential meas?xements, do not ground the recorder connected to the output. a. When recording the Keithley Model 370 Recorder offers complete compatibility with the Model 148. The output is sufficient to drive the Model 370 without the use of any re- corder preamplifiers. The Model 370 allows maximum capability of the Model 148. It has 1% linearity, 10 chart speeds and can float up to *500 volts off ground. Using the Model 370 with the Model 148 avoids interface problems which may be encountered between a meas- uring instrument and a recorder. b. The Model 370 is very easy to use with the Model 148. All that is necessary is con- necting the two units and adjusting an easily accessible control for full-scale recorder 12 1067

OPERATION L Trouble (seen on meter) Change in offset between ac and battery operation Possible Cause Low Battery Refer to paragraph 2-4 Very slow response time Excessive drift High source resistance paragraph 2-12 Improper shielding paragraph 2-13 I I Thermal emfs I paragraph 2-14 Improper connection to input paragraph 2-15 Excessive noise or needle High source resistance paragraphs 2-11,2-l instability improper shielding paragraph 2-13 Improper connection to input paragraph 2-15 Thermal emfs paragraph 2-14 Excessive temperature sensitivity Thermal emfs paragraph 2-14 presence of large, constant zero suppress Controls on paragraph 2-5 signal Thermal emfs paragraph 2-14 Improper connection to input paragraph 2-15 Excessive 8-cps beat at output I Improper location or poor I paragraph 2-13 or meter magnetic shielding I TABLE 4. Troubleshooting Operating Procedures. *he Table gives some possible sources of errors while using the Model 148 and refers to instructions to correct the situation. deflection. The furnished Model 3701 Input Cable mates with the output connector on the Model 148. On the most sensitive ranges of the Model 148, under some conditions, a" 8- cps beat may appear. This condition can be eliminated by mounting a 100~microfarad capac- itor across pins 14 and 17 in the back of the Model 370 Recorder. 2-10. ACCURACY CONSIDERATIONS. For sensitive measurements - 10 millivolts and below - other considerations beside the voltmeter affect accuracy. The Model 148 reads only the signal received at its input; therefore, it is important that this signal be properly transmitted from trle source. The following paragraphs indicate factors which affect ac- CllrWy: thermal noise, loading, shielding, thermal emfs and circuit connections. Table 4 also offers a quick reference to correct troubles which may occur. 2-11 THERMAL NOISE. a. The lower limit in measuring small potentials occurs when the Johnson noise, or thermal agitation, becomes evident. The amount of noise present in the source is show" in the following equations. 1. The thermal noise in any ideal resistance can be determined from the Johnson noise, equation: -As =4kTRF Eq. 1 where Er,, is the rms noise voltage developed across the voltage source; T is the temperature in degrees Kelvin; 1067 13

R is the source resistance in ohms; F is the amplifier bandwidth in cps; k is the Boltzmann constant (1.38 x lo-23 joules/OK). For an ideal resistance at room temperature (300°K), equation 1 simplifies to E rms = 1.29 x lo-lo (R F)112 Eq. 2 2. Peak-to-peak meter indications are of more interest than the rms value. Experi- mentally, the peak-to-peak Johnson noise is about five times the rms value. At room temperature, equation 2 becomes EPP = 6.45 x lo-10 (R F)li2 Eq. 3 where Epp is the peak-to-peak noise voltage developed across the voltage source. 3. The Model 148 bandwidth, F, can be estimated from the response speed, tr, by: F = 0.35/tr Eq. 4 The response speed varies with the range used and the source resistance. On the O.l- microvolt range when the source resistance is less than 10 ohms, for example, the band- width is greater that 0.7-cps. The maximum specified response speed for this situation is 0.5 second, so the 0.7-cps bandwidth is a minimum value. 4- As an example, determine the Johnson noise of a lo-ohm ideal resistor. Measured with the Model 148 on the 0.1~microvolt range and using equation 3, this becomes 17.1 x lo-10 volts peak-to-peak or 1.71 nanovolts peak-to-peak minimum. b. In general, good wirewound or low-noise metal-film resistors approximate ideal resis- tors, and equations 2 and 3 are nearly correct. If the source resistance is.composed of other materials, it may be necessary to include other terms in the equations to account for flicker, l/f, and current noise over and above the thermal noise. c. As seen in equations 2 and 3, the noise of even low resistance values becomes signi- ficant in the microvolt region. The noise in non-ideal resistors is even greater. There- fore, keep the source resistance as low as possible. Other effects of high source resis- tances are decreased response speed and added pickup of extraneous voltages. 2-12. INPUT RESISTANCE. The Model 148 is a feedback amplifier, and its input resistance is obtained by using high feedback factors. When the source resistance exceeds its physi- cal input resistance - the amplifier without feedback - the feedback is partially de- stroyed. Normally, do not exceed the maximum source resistance specified in Table 2; higher resistances may be used, but noise, offset, slow response time and instability may result. On the most sensitive ranges, the maximum source resistance is consistent with Johnson noise considerations. Z-13. SHIELDING. a. Due to its narrow bandwidth, the Model 148 is somewhat insensitive to ac voltages superimposed upon a dc signal at the input terminals. However, ac voltages which are large compared with the dc signal may drive the Model 148 ac amplifier into saturation, erroneously producing a dc output at the demodulator. Therefore, shield the circuit to the Nanovoltmeter input, particularly for low-level sources. 14 1067

OPERATION b. Improper shielding can cause the Model 148 to react in one or more of the following ways: 1. Needle jitter or instability, from 10% to 20% of full scale. 2. High offset (dc bias). Changing the power cord polarity or the connection between the LO and GND terminals may affect the amount of offset. 3. Slow response time, sluggish action and/or inconsistent readings between ranges. 4. Amplifier saturation. Observe the wave form with an oscilloscope connected to the DEMODULATOR TEST Jack (Figure 3). With the input shorted, it should approximate the wave form shown in Figure 6. If excessive pick- up occurs, the wave form will resemble that of Figure 7. The circuit will operate reasonably well as long as the wave formis not clipped, as shown in Figure 8. At this point a dc offset is introduced. --- FIGURE 6. Normal Wave Form at Demodulator with Input Shorted. Scale is 0.1 v/cm vertical and 10 msec/cm horizontal. FIGURE 7. Wave Form at Demodulator Shown with Some Pickup. Measurements are adequate; there is no offset but some noise. Scale is 0.5 v/cm vertical and 10 msec/cm ho,rizontal. FIGURE 8. Wave Form at Demodulator when Amplifier is Saturated. DC offset is intro- duced and there is greater noise. Note the Nanovoltmeter still reacts to the input signal, Scale is 5 v/cm vertical and 10 msecfcm horizontal. 0365 15

c. To minimize pickup, keep the voltage source and the Nanovoltmeter away from ac sources. Shield as carefully as possible. Connect all shields together at the low side of the input or at the LO terminal. The voltage induced due to a magnetic flux is proportional to the area of the loop. Therefore, minimize loop areas in the shield connections as well as the input circuitry. Connect the shield at only one point. Run all wires in the circuit along the same path, so the loop area is only the small difference in position of two adjacent wires. d. Strong third harmonic magnetic fields - 180 cps for ho-cps units - may create an 8-cps beat at the Nanovoltmeter output and meter. To reduce this effect, turn off all possible nearby sources, such as heavy-duty transformers. Remove the Model 148 and the measuring circuit as far as possible from the magnetic field. If removal does not greatly reduce the beat, magnetic as well as electrostatic shielding around the circuit may be necessary. For informa- tion concerning your particular shielding problem, contact Perfection Mica Corp., 1322 North Elston Street, Chicago, Illinois. e. Shielding is preferable to input filters. Resistive-capacitive filters add noise (see Johnson noise equation), and the resistance value must be sub- tracted from the maximum source resistance in Table 2. Inductive-capacitive filters tend to create loop instabilities with the Nanovoltmeter. Capacity alone across the input, however, is less likely to cause loop instabilities, and it may be used to filter ac components in some cases. 2-14. THERMAL EMF'S. a. Junctions between two dissimilar metals form a thermocouple and will de- velop an emf if there is a temperature difference between the metals. This effect may be seen by blowing on one junction and checking the meter indication. b. Thermal emf's can cause the following problems: 1. Meter instability or zero offset much higher than expected. Note, though, the Model 148 can have some offset (paragraph Z-5). 2. Meter is very sensitive to ambient temperature differences. This is seen by touching the circuit, by putting a heat source near the circuit, or by a regular pattern of instability, corresponding to heating and air con- ditioning systems or changes in sunlight. c. To minimize the drift caused by thermal emf's, use metals having the same thermoelectric powers in the input circuit. Gold, silver and low-thermal solder have a thermoelectric power within about i0.25 pv/"C of copper. This means a temperature unbalance of l°C between these metals would generate a thermal emf of about 0.25 microvolt. At the other extreme, germanium has a thermoelectric power of about 320 IJ-v/'C, and silicon will develop about 420 pv/OC against copper. Standard physical handbooks contain tables of thermoelectric powers of materials. Since the Model 148 input circuit is made of pure copper, use metals with nearly the same thermoelectric power. The best junction is copper to copper; however, slight amounts of copper oxide will cause a very slight ther- mal emf on the order of a few nanovolts per OC. The Model 1483 Kit contains all necessary equipment to make very low-thermal copper crimp joints. 16 0375

OPERATION d. Several other techniques will reduce the effects of thermal emf's. USC? the zero suppression circuit to buckout constant voltages. Keep all circuits from "pen windows, fans, air conditioning vents and similar sources which vary temperatures. If connections must be soldered, use only cadmium-tin low-thermal solder, such as supplied in the Model 1483 Kit. Unl.ike metals - including regular solder - may be used and low thermal cmf's obtained if a well-controlled oil bath or a good heat sink is used. Thermal voltages may be calculated Cram the thermoelectric power of the materials in the junction and the possible temperature difference between the junctions. 2-15. CIRCUIT CONNECTIONS. a. When measuring in the microvolt and nanovolt regions, consider the effect the physical connections will have on the potential being measured. IR drops, which in most circuits are insignificant, now become important. For example!, No. 20 AWG copper wire has a resistance of approximately 10 milliohms per foot. A l-milliampere current through a b-inch length of this wire will produce five microvolts. To reduce this drop to 0.5 nanovolt would mean using a wire 0.0006 inch long. . Four-terminal connections can , , often be used to eliminate this error. Refer to Figure 9. j ;it the zero suppress may be used If an unwanted IR drop is con- ~ 1 M":::d:48 1 to nullify the voltage. d. ' If the currents or resistances I in the measuring system fluctuate, / they will develop fluctuating voltages FIGURE 9. Using Model 148 with which will appear as noise or drict 4-Terminal Connections. in the system. 2-16. OPERATING FROM SOURCE OTHER THAN 117 VOLT, 60 CPS. a. If the ac power source is 234 volts, use a screwdriver to change the Line Voltage Switch on the back panel (Figure 3.) Change the fuse from l/8 ampere to l/16 ampere. Use only 250-volt MDL fuses. No other adjust- ment is necessary. b. For 50-cps ac power sources, change the sideband filter capacitors, Cl03 and C104. The Model 148 can operate satisfactorily from 60 or 50-cps sources, but the best ac rejection is achieved when the filter is set for the lint frequency. Use Keithley part C105-.109M (ClO3) and C45-.0155M (C104) for 50 cps. Refer to Figure 23 for component location. 2-17. RACK MOUNTING. (See Figure 10.) a. The Model 148 is shipped for bench use with four feet and a tilt-bail. 'The Model 4002 Rack Mounting Kit converts the instrument to rack mounting to the standard EIA (RETMA) 19-inch width. b. To convert the Model 148, remove the four screws at the bottom of each side of the instrument case. Lift off the top cover assembly with the 17

handles; save the four screws. To remove the feet and tilt bail from the bottom cover assembly, turn the two screws near the back. The two pawl-type fasteners will release the cover and allow it to drop off. Remove the feet and the tilt bail and replace the cover (2). c. Attach the pair of rack angles (3) t o the cabinet with the four screws (4) previously removed. Insert the top cover assembly (1) in place and fasten to ;he chassis with the two pawl-type fasteners at the rear. Store the top cover with handles, feet and tilt-bail for future use. I Item Keithley k See Fir. 10) Description Part No: Quantity 1 Cover Assembly 17162C 1 2 Cover Assembly, Bottom (Supplied with Model 148) 17695B 1 3 Angle, Rack 14624B 2 4 screw, Slotted, lo-32 UNC-2x1/4 (Supplied with Model 148) --- 4 5 Front Panel (Supplied with Model 148) --- 1 TABLE 5. Parts List for Moi 1 4002 Rack Mounting Kit. ,r. __--... ACOVER ASSEMBLY 4 Z COVER ASSEMBLY FIGURE 10. Exploded View for Rack Mounting. 18 0464:

CIRCUIT DESCRIPTION SECTION 3. CIRCUIT DESCRIPTION 3-1. GENERAL. a. The Model 148 consists of a chopper demodulator system followed by a dc amplifier. Feedback is applied to the whole loop. (See Figure 11.) b. A mechanical chopper converts the dc input signal to a 94-cps signal 'The ac signal is amplified, demodulated, dc amplified and applied co the meter. A feedback network samples the signal at the output and compares it to the input. The dc input signal and the feedback signal are compared in the input transformer primary. The transformer increases the voltage- difference signal between the two. The ac amplifier amplifies the dif- ference signal; line-frequency sidebands of the 94-cps signal are filtered out. The a~ signal is then demodulated by a saturated transistor switch and enters a dc amplifier, which has a feedback capacitor to filter out the demodulator ripple. The dc amplifier output is connected to the meter, the output terminals and the feedback network. The feedback resistors determine full-scale range. The zero suppress signal is con- nected to the feedback point in the input circuit. FIGURE 11. Block Diagram of Model 148 Amplifier Circuits. c. The power source for the Model 148 is either line voltage or the rechargeable battery. Voltage from either source is applied to a dc-to- dc inverter and then to three highly regulated supplies. The three supplies furnish power to the oscillator and the amplifier circuits. There is also a battery charging circuit to charge the battery when it is necess- ary and when the line voltage is connected. NOTE The circuit designations referred to in this section are for Schematic Diagrams 17351F, 17352D and 17353D found at the back of the manual. 0464 19

3-2. INPUT CIRCUIT. a. The dc input signal is connected through the high terminal of the INPUT Receptacle, JlOl, to the center contact of the mechanical chopper, GlOl. (See Figure 12.) The feedback signal is applied to the center tap of the input transformer, TlOl. .The chopper alternately applies a positive and a negative square-wave signal across each half of the primary. The magnitude of the square wave is proportional to the difference between the dc input and the feedback signals. TlOl steps up this signal and applies it to the grid of tube Vl. Chopper 1 0 L t "in VO FIGURE 12. Model 148 Input Circuit. The dc input signal, Vin, is applied to the mechanical chopper. The feedback signal, Vf (the dc amplifier output voltage, Vo, times the feedback ratio,,@ ), is applied to the transformer primary. The signal, Vd, stepped up by the transformer is the difference between the two, Vd = Vin - Vf, When the dc input signal is initially applied to the Model 148, Vf is zero and the voltage across the primary is entirely Vin. As the output voltage rises, Vf increases and Vd decreases to a small value. Vf = Vinj OrgV, = Vin. Only beta, which depends upon the RANGE and FUNCTION Switch settings, determines the amplifier gain. b. The input compartment is designed to insure high thermal stability and to minimize internal ac pickup. 1. Thermal stability is obtained in part by using only copper wire in the input circuitry. The input transformer primary and the mechanical chopper leads are pure copper. The input connector is 99.5% copper; the impurities add to the mechanical strength without creating large thermal emf's. The low voltage portion of the FUNCTION Switch uses pure copper pins and rotor. All connections to components are made with pure copper crimp lugs. Connections between components are made by bolting the lugs together - not soldering - to reduce thermal emf's. 2. The input compartment is doubly shielded against magnetic and electrostatic pickup on all sides. The wires are physically placed to maintain minimum loop area, further minimizing pickup. 20 0464

CIRCUIT DESCRIPTION c. The feedback network is formed from the output of the dc amplifier bacl; to the center tap of the primary of transformer TlOl. The RANGE Switch, SlO2: selects the feedback ratio used for each range. 3-3. AC AMPLIFIER. a. The ac amplifier circuit amplifies the 94-cps difference signal which corresponds to the dc input signal. The signal is applied to the grid of Vl and further amplified by tube V2. A low-noise silicon transistor, Q3, provides a high impedance load for V2. The signal is then ampl~ificd by transistors 44 and Q6. Potentiometer R109, between the Q3 emitter and Q4 base, adjusts the gain to compensate for beta variations. In addition, each stage has some local degeneration. Transistor 95 is for impedance matching. The difference signal is amplified by transistors (27 and 98, which also form a full-wave signal for demodulation. b. A series high-Q filter from the plate of V2 to circuit ground provides notch rejection at the power-line frequency sidebands. The values of ca- pacitors Cl03 and Cl04 depend upon the power-line frequency. Due to the high Q of the inductor, the filter forms sharp notches at 34 cps and 154 cps for 60-cps power lines and 44 cps and 144 cps for 50-cps power lines. ThC ac amplifier's 94-cps gain and phase characteristics are affected very little. c. The tube type and bias point of Vl are selected for low-noise oper- ation at 94 cps. The high-Q tuned circuit in the plate of Vl has a good signal-to-noise ratio, and it provides a narrow bandwidth around 94 cps. The tuned circuit's Q is lowered on the higher ranges for amplifier stability. 3-4. DKMODULATOR. Q9 and QlO in inverted configuration form a transistor switch demodulator. They convert the 94-cps wave from the ac amplifier into a dc voltage with ripple component. Resistors R123 and R124 sum the voltages from each to form a full-wave rectified signal. Jack 5102 allows access to observe the waveform. The 94-cps oscillator furnishes a square- wave drive for the demodulator. 3-5. DC AMPLIFIER. The demodulator signal is amplified by two low-drift, high-gain silicon transistors, Qll and 912, in differential configuration to com- pensate for temperature drift. Transistors Q13 and Q14 form the second amp- lifier stage. Total gain is about 500. The emitter follower output stage - transistors Q15 and Ql6 in pnp-npn configuration - draws little current at zero output. Diodes DlOl and D102 limit the output current, protect- ing Ql5 and Q16. b. A feedback loop with capacitor Cl15 around the dc amplifier acts as an integrator, filtering the ripple component of the demodulated waveform. The effective capacity, which is approximately the value of Cl15 times the dc amplifier gain, and the feedback factor (or open-loop gain) determine the response speed of the system. The capacitive feedback also lessens the noise in the amplifier outside the system bandpass. 0464 21

3-6. OSCILLATOR. The oscillator circuit, stable to 0.1 cps, has three parts: phase-shift network for a 94-cps signal, an amplifier to drive the chopper, and a transistor switch and phase compensation network for the square-wave demodu- lator drive. a. The phase-shift network consists of capacitors C301 through C303, resistors R319 through R321, and the combined resistance of R303 and R318, which bias transistor Q17. The input impedance of the emitter follower, 917, has little loading effect on the effective value of this last resistance. Transistor Q18 compensates for signal losses in the phase-shift network. Potentiometer R319 adjusts the signal frequency. Resistor R322, the filament of a low-power sub- miniature tube, Raytheon CK6418, provides variable degeneration to maintain a sine wave output to the next stage. b. From the phase-shift network, the signal is amplified and used to drive the chopper. Transistor Q19 matches the impedance of transistor 920 to the phase-shift network. Potentiometer R313 adjusts the signal amplitude. From transistor Q20, the signal is applied to the primary of transformer T301, which drives the class B stage, transistors 922 and 923. After amplification the sine-wave signal is applied to the mechanical chopper, GlOl. Transistor 921 develops the bias voltage for the class B stage, providing ambient temper- ature compensation for the chopper-drive signal amplitude. The center taps of transformers T301 and T302 supply dc current for the class B stage. T3;;. The chopper drive signal is also applied to the primary of transformer The transformer drives transistors Q24 and Q25 through a phase-compensa- ting network, resistors R308 to R310, R323 and capacitor C309, which compensates for the chopper phase shift. The transistors alternate between saturation and cut off to form a square-wave drive for the demodulator, transistors Q9 and QlO. 3-7. ZERO SUPPRESSION. The zero suppress circuit provides a regulated voltage from the power supplies to buckout steady background potentials in the input signal. The lo-turn FINE Control, potentiometer R168, is connected between -12 and +12 volt outputs. The resistors R165 to R167 and R172 in the COARSE Switch, S103, further divide the voltage. When the FUNCTION switch, SlOl, is in the MILLIVOLTS position, the suppress voltage is applied directly to the primary of transformer TlOl. When the FUNCTION Switch is in MICROVOLTS pos- ition, the suppress voltage is divided by an evenohm, 0.25% resistor, R140, copper resistor R137A, and a copper resistor R141. Using copper resistors for the lowest voltage points shunted by evenohm resistors provides thermal and re- sistive stability. 3-8. POWER SUPPLIES (See Figure 13.) The power supply for the Model 148 is powered by an unregulated supply from the line voltage or rechargeable battery. Either source feeds a dc-to-dc inverter and three highly regulated supplies with outputs of +12, -12, and +1.2 volts. These power all the other Model 148 circuits. a. The line voltage, battery and battery charging circuit are controlled through the POWER SUPPLY Switch, S201. When the switch is in AC, the battery is charged if necessary and the power supply uses line voltage. When the switch is in OFF, the battery charging circuit will operate if necessary; all other circuits are off. When the switch is in BATTERY, the power supply usas the battery; the other two circuits can not operate. 22 0464

CIRCUIT DESCRIPTION FIGURE 13. Block Diagram of Model 148 Power Supplies. b. The unregulated supply consists of a full-wave rectifier, diodes D212 and D213, and a dropping resistor, R232. The AC CONNECTED Lamp, DS201, is in series with resistor R226, which is connected directly across this supply. For battery operation the primary of transformer T201 is disconnected. c. Voltage from the unregulated supply or the battery is applied to the dc-to-dc inverter circuit. Transistors 428 and Q29 form a switching network to supply an interrupted voltage to transformer T202. The switching fre- quency is about 2 kc, well away from the carrier frequency. Transformer T202 has a saturable ferrite core. The inverter circuit supplies voltages to the three regulated supplies, which are basically the same series regulator design. d. For the +12 volt supply, diodes D206 and D207 full-wave rectify the signal from transformer T202. The signal is applied to the pass transistor, Q30. The output of Q30 is divided by resistors R208 and R209 and compared to the zener diode reference, D205. Transistors Q34 and Q33 amplify any potential difference and apply a signal t,o the base of transistor 932. Diodes D204 and D205 fix the emitter voltage of 432; therefore, the collector voltage of Q33 directly determines the current through Q32, which comes from the -12 volt supply. The current drop through resistor R216 determines the voltage at the base of transistor Q31, and therefore .the output voltage through the base-emitter junction. Diode D203 limits 0464 23

the base-to-emitter voltage of the 430 and 931 combination, thus also limit- * ing the current which it will pass. Diode D203 protects the pass transistor, Q30, if output of the supply is shorted, e. For the -12 volt regulated supply, diodes D210 and D211 full-wave rectify the signal from transformer T202. The signal is applied to the pass transistor, Q35. The output of Q35 is divided by resistors R217 and R218, thereby compar- ing it to the +12 volt supply, using ground as a reference. Transistors 938 and 939 amplify any potential difference and apply a signal to transistor Q37. Transistors Q35 and Q36 form a Darlington combination, and work similarly to that in the ,112 volt supply. The differences are that the -12 volt supply draws a higher current than the +12 volt supply, and therefore uses two diodes, D208 and D209, to protect the pass transistor. The negative "bootstrap" current supply is from a filter, resistor R225 and capacitor C210. f. The +1.2 volt supply operates in the same manner as the 1~12 volt supply with these differences. The output of the pass transistor, Q40, is compared to the output of the t12 volt supply divided down one tenth. The operating voltages for the comparator stage, 443 and 444, are obtained from the -h2 and -12 volt supplies. Except for the comparator stage, npn transistors are used. 3-9. BATTERY CHARGING CIRCUIT. a. The battery charging circuit operates when the POWER SUPPLY Switch, 5201, is in AC or OFF position, and only when the battery needs charging. b. The battery voltage is compared to a reference by two cascaded transistors, 926 and Q27. When it is low, a charging current from transformer T201 is applied to the battery through the BATTERY CHARGING lamp, DS202, transistor 927 and diode D216. The reference is zener diode D214; the reference voltage is adjusted by potentiometer R228. The difference between the battery and the reference poten- tials determines the magnitude of the charge current through Q27. A silicon diode, 0216, prevents the battery from being run down because of leakage currents through Q27, a germanium power transistor. Diode D215 limits the base-to- emitter voltage of the Q26 and Q27 combination, so no more than 400 milliamperes (the rated maximum charge current of the battery) can flow in the circuit. c. This circuit protects the battery. It decreases the charging current to a trickle-charge rate as the battery terminal voltage approaches the reference voltage. It also limits the charge current if the battery was used beyond its ampere-hour capacity, Note, however, that the battery can be damaged if it is used far beyond its capacity. A polarity reversal of a cell may occur, causing heavy circulating currents within the battery. 24 0464,

MAINTENANCE SECTION 4. MAINTENANCE 4-1. GENERAL. a. Section 4 contains the maintenance, troubleshooting and c.libratzon pro- cedures for the Model 148. It is recommended these procedures be followed as closely as possible to maintain the instrument's specifications. b. The Model 148 requires no periodic maintenance beyond the normal care required of high-quality electronic equipment. Components operate well below maximum ratings. Principal maintenance is an occasional chopper replacement. (See paragraph 4-3.) Occasional verification of meter calibration should show any need for adjustment. 4-2. PARTS REPLACEMENT. a. The Replaceable Parts List in Section 5 describes the electrical com- ponents of the Nanovoltmeter. Replace components only as necessary, and use only reliable replacements which meet the specifications. The Model 148 uses no special critical parts except for resistor R322, which is a subminiature tube filament, and the components listed in Table 6. Make sure parts coded 80164 in the Replaceable Parts List are purchased only from Keithley Instruments or its distributors. b. The physical location of components in the input compartment is critical. Place replacement parts in the exact position shown in Figure 14. Circuit loops will introduce extraneous ac signals; see paragraph 2-13. The order of the copper lugs on the insulated posts greatly affects offiset and noise in tllc Model 148. Tag or record the number on each lead as it is removed. Replace in reverse sequence. Table 6 lists components which have lugs crimped on them. When replacing these parts, clean the lug with a non-metallic abrasive, such as Scotch-Brite found in the Model 1483 Kit, or its equivalent. Follow the procedures necessary for good low-thermal connections. ComDonent Circuit Desig. Keithley Part No. Battery pack assembly BA201 Mechanical chopper assembly (See paragraph 4-3.) GlOl Input connector assembly JlOl Copper feedback resistor assembly R137 Evanohm resistor assembly R139 Evanohm resistor assembly R140 Evanohm resistor assembly R14.1 Function switch plate assembly SlOl Input transformer assembly TlOl Model 148' 17689A 17638A 17627A 17635A 17636A 17637A 16883A 17623B TABLE 6. Model 14,8 Pre-assembled Components. These parts have lugs crimped on them and the proper lead length. Use only Keithley parts for replacements; follow instructions given in paragraph 4.-Z. 1266 25

FIGURE 14. Model 148 Input Compartment. Note exact physical location of parts. If replacing, duplicate location and order of leads on posts. Figure 21 gives circuit designations. 4-3. MECHANICAL CHOPPER REPWXMKNTS. a. The mechanical chopper is designed for long life. However, since it is mechanical, it will eventually wear and become noisy. At this point, replace- ment is necessary. b. Removal Procedures. 1. Disconnect the chopper drive coil at connector 5302 (Figure 20). Carefully remove the three thumb screws in the input compartment and the three chopper lead lugs. 2. Carefully slide the degaussing coil, L302 (Figure 20), from the chopper body; remove the old chopper. c. Replacement Procedures. 1. Slide the degaussing coil, L302, over the new chopper body from the bottom. Orient so that the cut-out in the coil fits over the chopper drive lead. 2. Mount the chopper and coil in the input compartment. Dress leads as shown in Figure 14. 26 0365

MAINTENANCE 3. Check the instrument for proper operation. Follow paragraph 4-9, subparagraph b, steps 1, 2 and 3. d. Degaussing Coil Adjustment Procedures. 1. With the input shorted, use the ZERO SUPPRESS Controls to generate a signal through the Model 148. Use a differential input to the Type 503 Oscilloscope (-i- and - inputs) to observe the wave form between the emitters of transistors Q9 and QlO (Points P and Q, Figure 25). 2. The wave form amplitude varies as the degaussing coil is moved along the chopper body. Potentiometer R301 (Figure 21) determines the effect of the coil on the wave form. Adjust both the coil and the potentiometer for minimum amplitude. Reverse the red and black leads to the degaussing coil if necessary. 3. An 8-cps beat at points P and Q may be present. Use battery opera- tion to reduce the beat; refer to paragraph 2-3. 4-4. TROUBLESHOOTING. a. The following procedures give instructions for repairing troubles which might occur in the Model 148. Use these procedures to troubleshoot and use only specified replacement parts. Table 7 lists equipment recommended for troubleshooting. If the trouble cannot be readily located or repaired, con- tact Keithley Instruments or its representatives. Paragraph 2-17 describes how to remove the Nanovoltmeter cover. b. Paragraphs 4-6, 4-7 and 4-8 give step-by-step procedures for trouble- shooting and checking out the power supply, oscillator and amplifier circuits. Follow these in the order given. Tables 9, 10 and 12 are troubleshooting tables for these circuits. Also refer to Section 3 to find the more crucial components and to determine their function. The Schematic Diagrams, 17351F, 17352D and 17353D, contain the voltages at certain points in the circuit. NOTE Before troubleshooting inside the Model 148, check the external circuits (paragraph 4-5). Always check out the power supply and the oscillator circuits before touching the amplifier circuits. The amplifier circuits often ap- pear faulty only because of a defect in the power supply or oscillator circuits. 4-5. PRELIMINARY TROUBLESHOOTING PROCEDURES. a. Before troubleshooting, check the outside circuits to the Model 148. Isolate the Nanovoltmeter from all external effects: 1. Disconnect all outside circuits from the INPUT and OUTPUT Recep- tacles, and GND and LO terminals. 0972 27

Use Monitor oscillator frequency. Keithley Model 662 Cuardrd DC Differen- tial Voltmeter RCA Model WV98113 Sunior Vol.tohmyst, 11 m input resistance, .!3-;< accuracy, 0 to 1500 volts dc. Check voltage at output term- inals. Check dc voltages through- out circuits. Tektronix Typ? 503 Oscilloscope, dc to Check wave forms for trouble- 450 kc. shooting and calibrating. 'CABL,C 7. Equipent Recommended for Troubleshooting and Calibrating then Model 148. 'USC. these instruments or their equivalents. 2. Connrci. ii low-therraal short across the INPUT Receptacle. The best connector ins a I%&1 1486 male low-thermal connector with a short length of pure CUI)~:~I: No. 18 or No. 20 wire rimped between the two pins. The next best is a Hodcl 1481 Low-Thermal Input Cable with the clips connected together‘ !0xr) the cable as far as possible from ac sources, and avoid a loop where i:h,~: alligator clips are connected. 3. Set t.lh,. Z'KRD SUPPRESS COARSE Control to OFF. b. 1f hac:~~-~:~~~~ operation is trouble free, set the POWER SUPPLY Switch to BATTERY. li!sconnect the power cord from the power line. Battery operation eliminates maoy ground-loop connection problems with the test equipment. c. lf a<. opc?ration is used, check the Line Voltage Switch for correct position and hire Fuse for correct rating. NOTE Often; after checking out according to paragraph 4-5, the Model 148 wj.11 ilunction normally, This points to problems in the circuits outs:iGt the Nanovoltmeter. Refer to Table 4 to check the external circuit. 4-6. CHECK WI' AND CALIBRATION PROCEDURES. a. The following procedures give the steps to check out and calibrate the Model 148 circuits. If a circuit fails to check out at any point, refer to the circuit's troubleshooting table. Continue as long as the points check out. Use the equipment listed in Table 7. b. Procedures are given for the power supply, oscillator and amplifier circuits. These clover the principal adjustments to bring the instrument within speclficntions. 28 1067

MhINTENANCE C. If the Model 148 is not within specifications after performing these checks and calibrations, return the unit to Keithley Instruments for further checkout, or follow the troubleshooting procedures to find the fault. NOTE Make sure the power supply and oscillator circuits arc operating correctly before checking the amplifiers. All circuits depend upon properly functioning power supplies. If taken out of order. the resulting adjustment may be faulty. 4-7. POWER SUPPLY CHECK OUT AND CALIBRATION. a. All circuits depend upon the power supplies. Therefore, the ~+12, -12 and +1.2 volt outputs mst be operating correctly before further checks are made. If the power supply fails to check out at any point, refer to Table 9. After clearing the trouble, continue the check. b. Procedures for CheckFng Regulated Power Supplies. 1. Connect the low-thermal shorting plug to the INPUT. Set the Model 148 controls as follows: POWER SUPPLY Switch OFF RANGE Switch 100 FUNCTION Switch MILLIVOLTS ZERO SUPPRESS COARSE Control OFF Line Voltage Switch Set to line voltage 2. Plug in the power cord. The AC CONNECTED Lamp should light. 3. Measure the voltage at the Yellow-White wire on the POWER SUPPLY Switch front deck (Point A, Figure 20). It should be -18 volts dc ,2 vdc. 4. Turn the POWER SUPPLY Switch to AC. Use the oscilloscope to check the wave form at point E (Figure 26) in the dc-to-dc inverter. Wave form should resemble that in Figure 15. 5. Measure the signal levels and ripple with respect to low of the three regulated supplies. Table 8 gives the values. Regulated Maximum Ripple, Resistance Power Test Point, Signal Level, Millivolts to Ground, SUPPlY Figure 21 Volts dc Peak-to-Peak Ohms +12 volt B 11.6 to 12.8 0.3 850 2100 -12 volt C 11.9 to 13.1 2.0 460 + 70 cl.2 volt D 1.16 to 1.28 0.2 20!~ 3 TABLE 8. Signal Level, Maximum Ripple and Resistance for Regulated Power Supplies. 9664 29

TROUBLE PROBABLE CAUSE SOLUTION No voltage at point Blown fuse. Check for shorted transformer A (Fig. 20) T201 or wiring; then replace fuse. D212, D213 or R232 Check components; replace if OpelI. faulty. Irregular wave form Overloaded regulators Check resistances at power supply at point E (Fig. 26) Q29 faulty. Incorrect voltage at Defective D205, Q33, Check components; replace if points B, C and D Q34, 438 (0~. 439)s faulty. (Fig. 21) D204, D212 Incorrect voltage Shorted Vl or V2 Check Vl and V2 filament. only at point D filaments (Fig. 21) Defective Q43 or Q44 Check components; replace if faulty. High ripple at Defective oscillator See paragraph 4-8. points B, C and D (Fig. 21) Defective D204, D212, Check components; replace if D205, 433, 434, Q38 faulty. or Q39. High ripple only at Defective Q43 and/or Check components; replace if point D (Fig. 21) 444. faulty. Unable to adjust for Defective D214, R227, Check components; replace if -8.2v at point G R228, R229 or 426. faulty. (Fig. 26) High ripple at B, Low battery voltage. Charge battery (paragraph 2-4). C and D (Fig. 21) on battery oper- ation only. TABLE 9. Troubleshooting Table for Power Supply and Battery Charging Circuits. c. Procedures for Charger Circuit. 1. Disconnect the battery pack; do not let the terminals touch the chassis. Connect the Nanovoltmeter to the ac power line. Put the POWER SUPPLY Switch in AC position. 2. Set the charger bias voltage to -8.1 volts dc at point G, Figure 26. Adjust potentiometer R228 (Figure 27) for this value. 30 0664

MAINTEXANCE FIGURE 15. Correct Wave Form in dc-to-dc 1nverter. Point E, Figure 26, was monitored. Scale is 5 v/cm vertical, 0.2 msec/cm horizontal. 3. Connect the battery; make sure the polarity is correct (red to red). The positive side of the battery is ground. The BATTERY CHARGING Lamp should light, showing the charging circuits work. The lamp brightness directly indicates the charge current - the brighter the light, the greater the current. 4. After connecting the battery pack, the bias voltage may change. This is normal and no readjustment is required. 4-8. OSCILLATOR CHECK OUT AND CALIBRATION. a. The oscillator circuit drives the demodulator and the chopper. If the power supplies check out, continue on the oscillator. If the oscillator fails to check out at any point, refer to Table 10. After clearing the trouble, continue to check. b. Procedures. 1. connect the Type 503 Oscilloscope and the Model 5512A Electronic Counter to point F (Figure 21). 2. Set the oscillator frequency to 94 cps to.1 cps with potentiometer R319 (Figure 28). 3. Set the oscillator signal amplitude to 15.4 volts peak-to-peak kO.2 v peak-to-peak, measured on the oscilloscope. Adjust with poten- tiometer R313 (Figure 28). 4. Check the wave form at point F. It should be essentially sinusoidal, as in Figure 16. 0664 31

NOTE If transistors 42.1, 922 or Q23 are replaced, it my be necessary to change resistor R307. A 27-kilohm resistor should provide the proper bias for 422 and 423. The wave form at point F should resemble Figure 16. If it does not but resembles Figure 17, use a 15-kilohm resistor for R307. Fl in Oscillator Circui:t. 2 msec/cm horizontal. Scale is 2 v/cm &rtIcal, FIGURE 17. Improper Wave Forms at Point F (Figure 21) in Oscillator Circuit. Wave A indicates the wrong bias; wave B is distorted. Scale for both is 2 v/cm vertical, 2 mseclcm horizontal. 32 0664

MAINTENANCE TROUBLE PROBABLE CAUSE SOLUTION Jnable to adjust fre- Shorted chopper drive Disconnect chopper at 5302. &lency to 94 cps circuit Check for 94 cps at Q19 emitter (Point H, Figure 28). Check fol shorted wiring and chopper coil. Distorted, off-fre- Defective 417, 918 Voltage at point H should be 1 quency wave form at or Ql9 to 2 volts peak-to-peak, sine point H with chopper wave. If not, check components; disconnected replace if faulty. Low voltage, dis- Defective Q17, Q18, Cheek components; replace if torted wave form at Q19 or R322 (Fig. 17b) faulty. >oint F Defective 420, 421, Check the voltages, y20 to Q23, Q22, Q23 or R313 given on schematic 173531). Kc- (Fig. 17 a or b) place faulty components. Improper bias to Adjust R307 as in note. 922 and Q23 ( Fig. 17a) Jnstable frequency. Defective 417, R319, Check components; replace if C301, C302, C303 or faulty. Q17 or R319 are most R321, R320, R303, R318 likely parts. TABLE 10. Oscillator Circuit Troubleshooting Table. 4-9. AMPLIFIER CHECK OUT AND CALIBRATION. a. The check out and calibration of the amplifier circuits is divided into two parts: operational check and gain calibration. The operational check does not have to be followed by gain calibration. Use this to check the Model 148 operation. If the amplifiers fail to check out at any point, refer to Table 12. After clearing the trouble, continue the check. NOTE Check the power supply and oscillator circuits before adjusting the amplifiers. If the other two circuits are changed, the amplifier circuit nay need recalibration. b. Operational Check Procedures. 1. Connect the low-thermal shc,.ting plug to the INPUT. Set the front panel controls as follows: POWER SUPPLY Switch BATTERY RANGE Switch 0.3 FUNCTION Switch MICROVOLTS ZERO SUPPRESS COARSE Control OFF ZERO SUPPRESS FINE Control At one end of rotation 0664 33

2. On the 0.3-microvolt range, the meter offset should be less than 0.2 microvolt (66% of full scale). It may be higher if the shorting plug is not used. 3. Switch the ZERO SUPPRESS COARSE Control to 1; the meter should shift 0.2 to 0.16 microvolt. 4. Connect the Type SO3 Oscilloscope to the Model 148 OUTPUT. Set the oscilloscope amplifier to dc coupling, 0.2 volt/cm, time base to 0.1 or 0.2 second/cm. Set the Model 148 to the 0.1~microvolt range. Set the ZERO SUPPRESS COARSE Control to 1 to obtain a O.l-microvolt signal. The response time (from 10% to 90% of final value) should be between 0.2 and 0.4 second. Adjust potentiometer RlOV (Figure 25) for this value. NOTE Potentiometer RlOV Is a critical control. It adjusts the amplifier gain which affects Jutput ripple, input resistance and maximum source resistance as well as response time. Adjust this control only if one of these characteristics is slightly out of specifications. c. To properly calibrate the Model 148 amplifier gain, an accurate micro- volt-millivolt source is necessary. The value of this calibration depends very much on the source. If one is not available, it is recommended that the gain be calibrated by Keithley Instruments. If a source should be constructed, here are some guides. 1. Use good low-thermal construction techniques (paragraph 2-10, and following). 2. The source accuracy is determined by the accuracies of the divider and the power supply. 3. Divide the source to the microvolt level with an accurate low-thermal divider. Keithley Part R107 is a good low-level copper resistor with good low-thermal performance. Its 1OOO:l ratio is accurate to better than 0.5%. Use standard ratio techniques to measure the exact ratio. If the R107 is used, shunt it with about an 100~ohm evanobm resistor. This reduces temp- erature dependance of the divider to about 60 ppm/OC, from the resistance temperature coefficient of copper of about 4000 ppm/OC. d. Gain Calibration Procedures. 1. Connect the microvolt source to the Model 148 INPUT. 2. Connect the Model 662 Differential Voltmeter to the Model 148 OUTPUT Receptacle. 3. Before applying power to the microvolt source, adjust the ZERO SUPPRESS Controls for zero output at the output terminals. 4. For a given full-scale input signal, measure the output voltage. It should be 1 volt dc fl% for all ranges. 34 1067

MAINTENANCE 5. Check the resistors in the RANGE Switch by following the ranges in Table 11. If these ranges check out, all ranges are within specifications. If a range fails to check, refer to Table 12. Rezero using the Zero Suppress Control before each check. 6. After calibrating the amplifier, adjust the input voltage (or zero suppression) for full-scale outputs as shown on the differential voltmeter, on any range from 1 microvolt and above. Adjust potentiometer R136 (Figure 25) for exactly full-scale meter deflection. Range Resistor Used In RANGE Switch 100 Millivolts and all other ranges Rl37B, Rl39, R144 0.01 and 0.1 millivolt &J.@, Rl5Q 0.1 Millivolt R170 0.3 Millivolt R171 1 Millivolt R145 3 Millivolts R146 10 Millivolts R147 30 Millivolts R148 100 Millivolts and 100 Microvolts R137 ratio TABLE 11. Range Checkout. If these ranges are correct, all Model 148 ranges are correct. If any fail, check the listed resistor. 0664 35

Short in feedback network. Make sure lugs do not touch each other or the copper plate in input compartment. Check resistances. Maladjusted degaussing coil. Adjust (paragraph 4-3). Random zero drift, tens of nano- Noisy chopper Replace chopper; see paragraph 4-3. volts or more; sometimes reduced if the cabinet slapped. Response speed is good. Zero drift greatly affected by Maladjusted or dirty FUNCTION Loosen set ;xews on rotor hub (Figure slight movement of FUNCTION Switch. ); slide rotor zway from pins. Clean Switch within a setting. rotor and pins with non-metallic abrasive. Adjust such that the rotor is flush with and makes contact with all three pins consecutively, two at a time. Zero drift very temperature Contaminated INPUT Receptacle, Clean INPUT Receptacle with non-metallic sensitive. shorting plug, or connection abrasive. If contamination goes below in input compartment. plated surface, replace connector. Clean lugs with non-metallic abrasive; be sure to return to posts in original order. Response speed very slow, Low ac amplifier gain, due to Set to O.l-microvolt range, ZERO SUPPRESS possibly offset also high. bad active element, COARSE to 3, FINE to an easily readable Cannot adjust to specifications signal. With oscilloscope, check for with R109. square wave at Vl, grid, and sine wave at input and output of each succeeding stage. Check dc voltages, Vl through 98, given on schematic 17351F. Replace faulty components Improper amplifier phasing See paragraph 4-10. If it is incorrect, use lissajous patterns to check phase from grid Vl through each stage to base Q7. Shifts of up to about 300 dre acceptable, Check capacitors and active elements. TABLE 12 (Sheet 1). Amplifier Troubleshooting Table.

Low gain in dc amplifier. Unsolder and lift one end of R123 and R124. possibly offset also high. See points M and N, Figure 25. Apply 10 t( Cannot adjust to specifications 1OOmv to base of Qll to zero meter. Chang< with R109. input by 1 millivolt; output should shift 0.3 to 3.0 volts. If not or if more than 1OOmv is required to zero, check transis- tors, beginning with Qll and Q12. Qll and Q12 are matched for offset. Replace only with parts purchased from Keithley. Leaky or shorted C115. Check; replace if faulty. Demodulator does not "clamp" Defective Q9, QlO, 424 Check for sine wave -t secondary of T302, during one-half cycle (Fig- or 925. square wave at collector 924 and 925 and ure 18). base Q9 and QlO. Replace faulty componentr Greater than 20-1~ peak-to-peak Instrument located near high Try turning off possible sources one ripple at output terminals on HO-cps magnetic field, such by one. Move instrument from field ac power. On battery operation, as poorly shielded heavy-duty source. output ripple is above 5 mv p-p. transformer. lOO-millivolt and all other R144, R139, or R137 out of Check resistors; replace if faulty. ranges out of calibration, tolerance. all same direction. Only 0.01 and 0.03~microvolt or millivolt ranges out of calibration. R149 or R150 out of tolerance. Check resistors; replace if faulty. All microvolt ranges out of calibration. The millivolt ranges are good. R137, ratio B to A out of tolerance. Check resistor; replace if faulty. One range out of calibration. Corresponding resistor in Table 11 out of tolerance. Check resistor; replace if faulty. TABLE 12 (Sheet 2). Amplifier Troubleshooting Table.

FIGURE 20. Top View of Model 148 Chassis. Location of components, printed circuits and some test points is shown above. Refer to Parts List for circuit designations. 38 0365

MAlNTENANCE i i FIGURE 21. Bottom View of Model 148 Chassis. Locations of components and some test points is shown above. The input compartment is shown without its shield. Refer to Parts List for circuit designations. * Connect to point F at either place, not to both points simultaneously. 0664 39

MAINTENANCE FIGURE 24. Resistor Locations on Printed Circuit 76. Figure 25 contains callouts for the other resistors. FIGUM 25. Resistor and Test Point Locations on Printed Circuit 76. Figure 24 contains callouts for the other resistors. 0365’ 41

FIGURE 26. Resistor and Test Point Locations on Printed Circuit 74, Bottom Face. 9~ Connect to point E at either place, not to both points simultaneously. FIGURE 27. Component Locations on Printed Circuit 74, Top Face. 42 0664

MAINTENANCE FIGURE 28. Resistor and Test Point Locations on Printed Circuit 75. An alternate location for point H is shown in Figure 20. FIGURE 29. Capacitor and Transistor Locations on Printed Circuit 75. 0664, 43

FIGURE 30. Resistor Locations on RANGE FIGURE 31. Resistor Locations on Switch (S102). Figure 31 shows resistors RANGE Switch (5102). Figure 30 shows on opposite side. resistors on opposite side. 0 0 FIGURE 32. component Layout For PC-402. 44 0664

REPLACEABLE PARTS SECTION 5. REPLACEABLE PARTS 5-1. REPLACEABLE PARTS LIST. The Replaceable Parts List describes the com- ponents of the Model 148 and its accessories. The List gives the circuit designation, the part description, a suggested manufacturer and the Keithle; Part Number. The last column indicates the figure picturing the part. The name and address of the uunufacturers listed in the "Mfg. Code" column are contained in Table 14. 5-2. HOW TO ORDER PARTS. a. For parts orders, include the instrument's model and serial number, the Keithley Part Number, the circuit designation and a description of the part. All structural parts and those parts coded for Keithley manufacture (80164) must be ordered from Keithley Instruments, Inc. In ordering a part not listed in the Replaceable Parts List, completely describe the part, its function and its location. b. Order parts through your nearest Keithley distributor or the Sales Service Department, Keithley instruments, Inc. amp .Sllpl2TY~ M.il. No. Military Type Number MY Mylar Cbvar Carbon Variable CerD Ceramic, Disc n ohm ComP Composition PMP Metalized paper, phznolic case DC% Deposited Carbon Poly Polystyrene P pica (10-12) EAl Electrolytic, Aluminum EMC Electrolytic, metal cased Ref. Reference ETB Electrolytic, tubular ETT Electrolytic, tantulum v micro (10e6) f farad " volt Fig. Figure Var Variable hy henry w watt ww Wirewound k kilo (103) wwenc Wirewound encapsulated mega (106) or megohms WWVar Wirewound Variable M or meg zfg. milli (10w3) Manufacturer MtF Metal Film TABLE 13. Abbreviations and Symbols. 0664 45

(Refer to Schematic Diagram 17351F for circuit designations) CAPACITORS Circuit Desig. Value Rating Mfg. Keithley Fig. TYPO Code Part No. Ref. Cl01 .0143 uf 100 " Polv 84171 C45-.0143M 21 Cl02 O.Ol)lf 16 v CerD 71590 C238-.OlM 23 Cl03 (60 cps) .184 ILf 100 v MY 12673 C105-.184M 23 Cl03 (50 cps) .lOV llf 100 v MY 12673 Cl05-.109M 23 Cl04 (60 cps) .0135 bf 100 " Poly 84171 C45-.0135M 23 Cl04 (50 cps) .0155 ,Lf 100 v Poly 84171 C45-.0155M 23 Cl05 Not Used .liJ.f 50 " MY 84411 C41-.lM 23 Cl06 .22 pf 50 v MY 84411 C41-.22M Cl07 .012 vf 100 v Poly 84171 C45-.012M Cl08 4.7 pf 10 v ETB 05397 C71-4.7M Cl09 100 vf 15 v EA.1 29309 C210-100M Cl10 .Ol i.lf 600 v CerD 72982 C22-.OlM Cl11 Cl12 Cl13 Cl14 Cl15 25 jkf 100 iJf 10 pf 10 pf 25 I-if 16 v 15 v 20 " 20 v 10 v ETB 56289 EAZ 29309 ETT 05397 ETT 05397 ETT 05079 (non-polar) C104-25M C210-100M C80-10M C80-10M C106-25M 23 23 23 23 23 23 23 23 23 23 Cl16 Not Used Cl17 Cl18 Cl19 Cl20 C201 Not Used C7.02 Not Used C203 Not Used C204 c205 .05 pf 200 vf 0.047pf * 100 pf 100 Kf .Ol bf 100 vf 100 wf .Ol I.rf 100 IJ.f 100 iJf 600 v MY 3v EAl 200 " MPF 500 " POlY 56289 C62-.05M 14655 C48-200M 21 71590 c142-.O.O47M C-138-* 15 v FAl 15 " EAl 600 v CerD 25 v PMP 15 -.I PMP 600 v CerD 25 v PMP 25 v PMP 29309 C210-100M 23 29309 C210-100M 23 C206 c207 C208 c209 c210 c211 Refer to page 52 for higher designations. *Value selected at factory DIODES Circuit Mfg. Desig. TYPO Number Code 72982 C22-.OlM 23 29309 C211-100M 23 29309 C210-1OOM 23 72982 C22-.OlM 23 29309 C211-100M 23 29309 C211-1OOM 23 Keithley Fig. Part No. Ref. DlOl Silicon IN645 83125 RF-14 23 D102 Silicon IN645 83125 RF-14 23 D103 Zetler lN709 12954 DZ-21 ill04 zeIlC?r lN709 12954 DZ-21 46 0179

designations. MISCELLANEOUS PARTS Circuit Desig. Description Mfg. Keithley Fig. Code Part No. Ref. GlOl Chopper JlOl Receptacle, INPUT, Special Plug, Special, Mate of JlOl 5102 Jack, Telephone, DEMODULATOR TEST (Mfg. 83330 17689A 17638A CS-132 CS-65 No. 275) JlO3 Receptacle, Microphone, OUTPUT (Mfg. No. 80PC2F) --- Plug, Microphone, Mate of 5103 (Mfg. No. 02660 CS-32 02660 cs-33 8OMCZM) J202 connector (Mfg. No. PSC4SS15-12) 09962 cs-175 3301 5302 --- --- --- Connector (Mfg. No. PSC4=15-12) Receptacle 09962 cs-175 . Locking Ring (Mfg. No. 126-1430) 02660 es-165 . Receptacle (Mfg. No. 126-1429) 02660 CS-163 . Body (Mfg. No. 126-1425) 02660 CS-161 --- -ma --- Binding Post, LO (Mfg. No. DF21BC) 58474 BP-11B Binding Post, GND (Mfg. No. DF2lGC) 58474 BP-11G Shorting Link (Mfg. No. 938-L) 24655 BP-6 80164 80164 80164 20 2 3 3 -- 20 20 3 3 _- 0179 47

Circuit Desig. Description Mfg. Keithley Fig. Code Part No. Ref. LlOl L102 Ml01 SlOl a-- s102 --- --- s103 --- --s s201 --- 5202 TlOl T202 Choke, 200 hy 80164 Choke, 120/80 hy 80164 Meter 80164 Rotary Switch less components, FUNCTION 80164 Knob Assembly, Function Switch 80164 Rotary Switch less components, RANGE 80164 Switch Assembly with components, Range 80164 Knob Assembly, Range Switch 80164 Rotary Switch less components, ZERO SUPPRESS 80164 COARSE Switch Assembly with components, Coarse 80164 Knob Assembly, Coarse Switch 80164 Rotary Switch less components, POWER SUPPLY 80164 Knob Assembly, Power Supply Switch 80164 Slide Switch, 117 234 80164 Knob Assembly, Fine Potentiometer 80164 Transformer 80164 Transformer 80164 RESISTORS CH-1 20 CH-5 20 MB-14 20 ** 2 16323A SW-157 2 17632B 163238 SW-58 2 17626B 14838A SW-158 2 14838A SW-151 15110A 2 17623B 20 TR-65 20 Circuit Desig. Value Rating TYPO Mfg. Code Keithley Part No. Fig. Ref. RlOl 68 kS, .lO%, l/4 w Comp 01121 ~76-681CC1 32 R102 10 kn lO%, l/4 w Comp 01121 R76-10Kn 32 Rl03 4.7M0 lO%, l/2 w Comp 01121 Rl-4.7M0 32 R104 250 lin l%, l/2 w DCb 79727 RlZ-250K 25 R105 22 kn lO%, l/2 w Camp 01121 Rl-22K 24 Rl06 250 k.fi l%, l/2 w DCb 79727 R12-250K 24 Rl07 100 kn lO%, l/2 w camp 01121 Rl-100K 24 R108 22 kn lO%, l/2 w Comp 01121 Rl-22K 24 R109 100 ki2 lO%, .2 w CbVar 80294 RP40-100K 25 RllO 4.7 kJi lO%, l/2 w Camp 01121 Rl-4.7K 25 Rlll 22 kn lO%, l/2 w Comp 01121 Rl-22K 24 R112 27 ti lO%, l/2 w Camp 01121 Rl-27K 25 R113 10 kQ lO%, l/2 w Camp 01121 Rl-1OK 25 R114 10 kn lO%, l/2 w Camp 01121 Rl-1OK 25 R115 470 n lO%, l/2 w Comp 01121 Rl-470 24 we Contact the factory tar repiacement. 48 0179

4.7 kR 4.7 ksl 4.7 ba 8.2 kn lO%, l/2 w lO%, l/2 w lO%, l/2 w lO%, II2 w lO%, l/2 w lO%, l/2 w lO%, l/2 w l%, l/2 w l%, II2 w l%, l/2 w Comp 01121 Rl-4./K 24 Comp 01121 Rl-4.7K 24 camp 01121 Rl-4.7K 24 camp 01121 Rl-4.7K 24 Comp 01121 Rl-8.2K 24 R121 R122 R123 R124 R125 150 n 8.2 kn 10 kn 10 ka 50 kn Camp 01121 Rl-150 25 Comp 01121 Rl-8.2K 24 DCb 79727 R12-10K 25 DCb 79727 R12-10K 25 DCb 79727 R12-50K 25 R126 Rl27 RI28 R129 R130 50 kil 250 n 120 ICQ 120 kcl 12 kn l%, l/2 w l%, l/2 w l%, l/2 w l%, l/2 w lO%, l/2 w DCb 79727 R12-50K 24 DCb 19727 Rl2-250 24 DCb 79727 K12-120K 25 DCb 79727 Rl2-120K 25 C0mp 01121 Rl-12K 24 R131 12 ksl lO%, l/2 w Comp 01121 RL-12K 24 R132 25 kc, l%, l/2 w DCb 79727 Rl2-25K 25 R133 470 (1 lo%, 112 w C0mp 01121 Rl-470 24 R134 100 0 lO%, l/2 w Comp 01121 Rl-100 24 R135 8,6 ko, l%, l/2 w DCb 79727 R12-8.6K 25 R136 R137A & B RI38 R139 R140 2 kn 1 kn & li Not Used 111 0 1.11 ks? lO%, l/2 w WWVar 80294 RP35-2K 25 Special ww 80164 17627A 21 wwenc CO164 I.763511 wwenc 80164 17636A Rl41 R142 R143 R144 R145 10 kn Not Used Not Used 900 (1 99 kc1 l/4%, 113 w l/4%, l/3 w 5%, l/2 w Camp 80164 17637A l/4%, L/3 w l/4%, l/3 w l/4%, l/3 w l/4%, II3 w l/4%, l/3 w l/4%, 113 w l/4%, l/3 w 10x>, l/2 w lO%, l/2 w lO%, l/2 w lO%, l/2 w lO%, l/2 w lO%, l/2 w lO%, l/2 w wwenc wwenc K1.05-900 RlOS-99K R146 R147 R148 R149 R150 32.3 ICC2 9 ICS~ 2.33 ki, 900 n 100 n wwenc wwenc wwenc wwenc wwenc R105-32.3K R1.05-9K R105-2.33K RlO5-900 R105-100 Rl51 3.3 m C0mp Comp Comp C0Illp C0mp camp Comp 01686 01686 01686 01686 01686 01686 01686 01121 01121 01121 01.121 01121 01121 01121 Rl-3.3M Rl-680K Rl-330K RI-100K RI-47K RL-LM Rl-330K 21 21 21, 31 30 30 30 31 31 31 30 31. 31 31 31 30 30 R152 %- 680 kil R153 >'v 330 k0 Rl54 WOO kc) Rl55 "47 kQ R156 ?

camp 01121 Rl-22K 30 R161 6.8 k~ R162 3.3 kn R163 1 kn R164 470 a R165 4.7 m R166 1I"Tl R167 100 kn R168 10 kn R169 "33 kn R170 1 Xl R171 332 icn R172 10 kn R173 15 k0 RZOlNot Used R202Not Used R203Not Used R204Not Used R205Not Used lO%, l/2 w camp 01121 Rl-6.8K 31 lO%, l/2 w camp 01121 Rl-3.3K 31 lO%, 112 w camp 01121 Rl-1K 31 lO%, l/2 w camp 01121 Rl-470 31 l%, l/2 w DCb 79727 Rl2-4.7M e9< l%, l/2 w DCb 79727 RlZ-1M ?d< l%, l/2 w DCb 79727 RlZ-100K ?<9< 3%, 1.5 w wwvar 73138 RP41-10K 20 lO%, l/2 w camp 01121 Rl-33K 25 l/Z%, I.12 w MtF 75042 R61-1M 30 il4%, l/3 w wwenc 01686 R105-332K 30 l%, l/2 w DCb 79727 RlZ-10K w< l%, 1/8W, MtF 07716 R88-15K0 32 R206Not Used R207 1 kn R208 6.98 kb2 R209 6.98 kn R210 4.7 kn lO%, l/2 w l%, 112 w l%, l/2 w lO%, l/2 w lO%, l/2 w lO%, l/2 w lO%, l/2 w lO%, l/2 w lO%, l/2 w lO%, l/2 w l%, l/2 w l%, l/2 w l%, l/2 w lO%, l/2 w l%, l/2 w lO%, l/2 w lO%, l/2 w lO%, l/2 w lO%, l/2 w camp DCb DCb camp R211 2.7 kn R212 6.8 kn R213 22 11 R214 2.7 ks, R215 15 kn camp camp camp camp camp R216 22 kn R217 10 kn R218 10 k.Q R219 4.7 kn R220 10 kn camp DCb DCb DCb camp R221 10 ko R222 2.7 kn. R223 2.7 n R224 4.7 kfi R225 1 kn DCb camp camp camp 01121 79727 79727 01121 01121 01121 01121 01121 01121 01121 79727 79727 79727 01121 79727 01121 01121 01121 01121 Rl-1K 24 R12-6.98Kn 25 RlZ-6.98Kfi 24 Rl-4.7K 24 Rl-2.7K 24 Rl-6.8K 25 Rl-22 24 Rl-2.7K 25 Rl-15K 25 Rl-22K 25 RlZ-10K 25 Rl2-1OK 25 R12-4.7K 24 Rl-1OK 24 R12-10K 25 Rl-2.7K 25 Rl-2.7 24 Rl-4.7K 25 Rl-1K 24 Refer to page 53 for higher designations. k Nominal value, factory set. e* These resistors are located in S103, Figure 20. 50 0179

Q4NPN, Case TO-106 2N5134 Q5 2N1381 D1422 DICK 07263 07263 01295 :; 2Nl381 2N1381 01295 01295 Q8 2N1381 01295 2N1381 01295 2N1381 01295 Q~~NPN, Case TO-106 2N5134 07263 QlZNPN, Case TO-106 2N5134 07263 413 2Nl381 01295 414 2Nl381 01295 Q15 2N1605A 02735 Q16 2N651 04713 Refer to page 55 for designations Q17 to 925 and to page 53 for Q26 CO (229. 930 2N1381 01295 TG-8 22 431 2N1381 01295 TG-8 22 432 2N1381 01295 TG-8 22 Q33 2N1381 01295 TG-8 22 434 2N1381 01295 TG-8 22 Q35 PNP, Case TO-540139 02735 TG-50 22 Q36 437 Q38 Q39 Q40Not Used 2N1381 01295 2N1381 01295 2N1381 01295 2N1381 01295 TG-8 22 TG-8 22 TG-8 22 TG-8 22 Q41Not Used Q42Not Used Q43Not Used Q44Not Used VACUUM TUBES Circuit Desig. Number Mfg. Keithley Fig. Code Part No. Ref. TG-45 32 TG-45 32 TG-65 22 TG-65 22 TG-8 22 TG-8 22 TG-8 22 TG-8 22 TG-8 22 TG-8 22 TG-65 22 TG-65 22 TG-8 22 'TG- 8 22 TG-16 22 TG-9 22 Vl VZNot Used CK512AX 80164 EV-512AX 21 0179 51

circuit designations. CAPACITORS Circuit Desig. Value Rating 5Pe Refer to page 46 for lower designations. c212 500 kf 25 v IcAl C213 500 IJ.f 25 v FAl C214 .Ol pf 600 v CerD Refer to page 54 for higher designations. Mfg. Keithley Fig. Code Part No. Ref. 56289 C94-500M 27 56289 C94-500M 27 72982 C22-.OlM 27 DIODES Circuit Mfg. Keithley Fig. Desig. TYPO Number Code Part No. Ref. Refer to page 47 for lower designations. D212 D213 D214 D215 D216 D217 D218 D219 D220 Silicon Silicon ZfXXXC Silicon Silicon ZCSler ZCXltZr Rectifier Rectifier IN645 lN645 1N713 lN645 lN645 lN746A lN746A lN4148 1~4148 83125 RF-l.4 27 83125 RF-14 27 12954 DZ-14 27 83125 RF-14 27 83125 RF-14 27 01295 DZ-40 01295 DZ-40 01295 RF-28 01295 RF-28 Circuit Desig. MISCELLANEOUS PARTS Description Mfg. Keithley Fig. Code Part No. Ref. BA201 Battery Pack, 6-volt 4-amp-hr nickel- cadmium DS201 Bulb, AC CONNECTED, bayonet base (Mfg. No. 49) --- DS202 Light Socket, Red (Mfg. No. 81410-231) Bulb, BATTERY CHARGING, bayonet base (Mfg. No. 49) --- Light Socket, Amber (Mfg. No. 81410-233) F201 (117 v) Fuse, l/8 amp, 3 AG, type MDL F201 (234 v) Fuse, l/16 amp, 3 AG, type hDL --- Fuse Holder F202 FUSS, 1 amp, 8 AG X01 Terminal Block (Mfg. No. 3008) .I202 Connector (Mfg. No. 02-018-013-5200) 52 80164 Model 14,8920 08804 PL-23 72619 PL-5R 08804 PL-23 72619 PL-5A 71400 FU-20 71400 Fu-21 75915 FH-3 75915 m-1 83330 W-47 91662 CS-127 2 2 21 3 20 20 20 0179

Circuit Desig. Description Mfg. Keithley Fig. Code Part No. Ref. --- vs.. Line Cord Line Cord Clamp 80164 CO-5 3 80164 CC-4 5201 Rotary Switch (See pg. 48 ) 80164 SW-158 s202 Slide Switch, Line Voltage 80164 SW-151 3 T201 Transformer 80164 TR-63 20 RESISTORS Circuit Mfg. Keithley Fig. Desig. Value Rating TYPO Code Part No. RCf. Refer to page 50 for lower designations. R226 w20 0 .l%, 2 w ww 01686 R92-220 26 R227 330 n .l%, 2 w ww 01686 R92-330 27 R228 1 ki? lO%, l/2 w wwvar 80294 RP39-1K 27 R229 1.8 ku l%, l/2 w DCb 79727 R12-1.8K 27 R230 680 12 lO%, 112 w camp 01121 Rl-680 27 R231 10 n .l%, 2 w ww 01686 R92-10 26 R232 18 n .l%, 2 w ww 01686 R92-18 26 R233 100 (1 lO%, l/2 w CCJlllp 01121 Rl-100 27 R234 1.5 kn lO%, l/2 w camp 01121 Rl-1.5K 27 R235 1. 11 ww R236 75 kR Deb R237 10 k0 lO%, l/4 w Comp R238 10 kn lO%, l/4 w Comp Refer to page 54 for higher designations. 01686 R92-1 20 79727 RlZ-75K 27 01121 R76-10K 01121 R76-10K TRANSISTORS Circuit Desia. NUmber Mfg. Code Keithley Part No. Fig. Ref. Refer to page 55 for lower designations. Q’J6 2N1372 02735 ~27 2Nl535 04713 9253 2N651 04713 929 2N651 04713 Refer to page 51 for higher designations. TG-8 27 TG-7 27 TG-9 27 TG-9 27 ge Nominal value, factory set. 0179 53

Diagram 17353D for circuit designations. CAPACITORS circuit Desig. V.&-W Rating TYPO Mfr. Keithley Part No. Fig. Ref. Refer to page 52 for lower designations. c301 .22 pf 50 v MY 84411 C41-.22M 29 c302 .22 pf 50 v MY 84411 C41-.22M 29 c303 .l pf 50 v MY 84411 C41-.lM 29 c304 100 uf 15 v EAL 29309 C210-100M 29 c305 10 IJf 15 v PMP 56289 C93-10M 29 C306 100 jlf 15 v EAL 29309 CZlO-100M 29 c307 100 pf 15 v EAL 29309 C210-100M 29 C308 2 vf 50 " MPCb EC1 C-215-2M 21 c309 .22 I.lf 50 " MY 84411 C41-.22M 29 c310 470 pF 1ooov CerD 71590 DD-471 c311 470 pF 1ooov CerD 71590 DD-471 Circuit Desig. MISCELLANEOUS PARTS Description Mfr. Keithley Part No. Fig. Ref. 5301 J302 -__ --- --- L302 T301 T302 Circuit Desig. Connector (Mfg. No. 02-016-013- 5200) 91662 Connector . Nut (Mfg. No. 41-153) 02660 . Locking Ring (Mfg. No. 126-1428) 02660 . Plug (Mfg. No. 126-1427) 02660 Degausing Coil 80164 Transformer 80164 Transformer 80164 RESISTORS Value Rating 5Pe CS-126 20 CS-160 CS-164 CS-162 CH-6 20 TR-64 21 TR-68 21 Mfr. Keithley Fig. Part No. Ref. Refer to page 53 for lower designations. R301 2n lO%, 5 w R302 'W n lO%, l/2 w R303 12 Ml lO%, l/2 w R304 ZL l%, l/2 w R305 lO%, l/2 " R306 8.2 ksl lO%, l/2 w R307 a15 kcl lO%, l/2 w * Nominal value, factory set. wwvar camp camp DCb camp camp ComP 71450 RP34-2 21 01121 Rl-0 -- 01121 Rl-12K 28 79727 R12-5K 28 01121 Rl-4.7K 28 01121 Rl-8.2K 28 01121 Rl-15K 28 54 0179

lO%, l/2 w lO%, l/2 w camp camp camp 01121 Rl-4.7K 28 01121 Rl-4.7K 28 01121 Rl-4.7K 28 R311 R312 R313 R314 R315 Not Used 10 n 5m 6.8 ko 4.7 kc? lO%, l/2 w camp 01121 Rl-10 28 lO%, l/2 w wwvar 80294 RP39-5K 28 lO%, l/2 w camp 01121 Rl-6.8K 28 lO%, l/2 w camp 01121 Rl-4.7K 28 R316 2.5 ka l%, l/2 w DCb 79727 Rl2-2.5K 28 R317 10 m l%, l/2 w DCb 79727 Rl2-1OK 28 R318 12 kn lO%, l/2 w camp 01121 Rl-12K 28 R319 2 kn lO%, l/2 w wwvar 80294 RP39-2K 28 R320 2.2 !a l%, 112 w DCb 79727 R12-2.2K 28 R321 R322 R323 R324 R325 4 ka Lamp, 3v 4.7 kn 10 kn 10 kn l%, l/2 w lO%, l/2 w lO%, l/2 w lO%, l/2 w DCb 79727 R12-4K 28 CM-2158 CM PL-37 28 camp 01121 Rl-4.7K 28 camp 01121 Rl-1OK 28 camp 01121 Rl-1OK 28 TRANSISTORS Circuit Mfr. Keithley Fig. Desig. TyPe Desig. Mfr. Part No. Ret. Refer to page 51 for lower designations. Q17NPN, Case TO-106 2N5134 07263 Q18NPN, Case TO-106 2N5134 07263 Q19 2N1605 93332 Q20 2N1381 01295 Q21 2N1381 01295 Q22 2N1381 01295 923 2N1381 01295 Q24 2N1381 01295 425 2N1381 01295 Refer to page 53 for higher designations. TG-65 29 TG-65 29 TG-22 29 TG-8 29 TG-8 29 TG-8 29 TG-8 > with HS-2 29 TG-8 29 TG-8 29 MODEL 1481 REPLACEABLE PARTS LIST Keithley Description Mfr. Part No. Plug Assembly. Cable Assembly, 48 inches .Copper Alligator Clips (2) (Mfg. No. 6005) 80164 CS-132 80164 14731B 76545 AC-9 0179 55

Mfg. Keithley Description Code Part No. Plug Assembly 80164 CS-132 Cable Assembly, 10 feet 80164 14731B MODELS 1483, 1484 REPLACEABLE PARTS LIST Mfg. Keithley Used on Description Quantity Code Part No. Kit Model Crimp Tool for Copper lugs 1 #8 Nylon Screws 50 #8 Nylon Hex Nuts 50 Co~oer Bolt-on Lugs 100 CoKper Spade Lugs- Copper Hook Lugs Copper Splice Tubes Low-Thermal Cadmium-Tin Solder Copper Alligator Clips (Mfg. No. 6005) Shielded Cable Insulated #20 Copper Wire Non-metalic Abrasive 100 100 100 10 feet 80164 80164 80164 80164 80164 80 164 80164 80164 m-m 17340A 17339A 1733bA 17338A --- 1483 1483, 1484 1483, 1484 1483, 1484 1483, 1484 1483, 1484 1483, 1484 1483, 1484 10 76545 AC-9 1483, 1484 10 feet 80164 SC-5 1483, 1484 100 feet 80164 ws-1 1483, 1484 3 pads 80164 17774A 1483, 1484 TL-1 -mm I 01121 Allen-Bradley Corp. 05397 Kemet Co. Milwaukee, Wis. Cleveland, Ohio I 01295 Texas Instruments, Inc. 08804 Lamp Metals and Component Semi-Conductor Components Div. Dept. G. E. Co. Dallas, Texas Cleveland, Ohio 01686 RCL Electronics, Inc. Riverside,, N. 3. 02660 Amphenol-Borg Electronics Corp. Broadview, Chicago, Illinois 02735 RCA Semiconductor 6 Materials Div. of Radio Cqrp. of America Somerville, N. J. 04713 MDtoro1a, Inc. Semiconductor Products Division Phoenix, Arizona 09052 Gulton Industries, Inc. Alkaline Battery Division Metuchen, N. J. 12673 Wesco Division of Atlee Corp. Greenfield, Mass. 12954 Dickson Electronics Corp. Scottsdale, Ariz. 15909 Daven Co. Livingston, N. J. TABLE 14 (Sheet 1). Code List of Suggested Manufacturers. (Based on Federal supply Code for Manufacturers, Cataloging Handbook H4-1.) 56 0972

(Attach additional sheets as necessary.) Show a block diagram of your measurement system including all instruments connected (whether power is turned on or not). Also describe signal source. Where is the measurement being performed? (facton/, controlled laboraton/, out-of-doors, etc.)--_ What power line voltage is used? Variation? Frequency? Ambient Temperature? OF. Variation? OF. Rel. Humidity? Other? Any additional information. (If special modifications have been made by the user, please describe below.) *Be sure to include your name and phone number on this service form.