HK Instruments RHT-MOD Duct Series Installation Instructions
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Copyright HK Instruments 2021
www.hkinstruments.fi
Installation version 7.0 2021
INSTALLATION
INSTRUCTIONS
HUMIDITY TRANSMITTERS
RHT-MOD Duct Series
• READ THESE INSTRUCTIONS CAREFULLY BEFORE
ATTEMPTING TO INSTALL, OPERATE OR SERVICE THIS
DEVICE.
•� Failure�to�observe�safety�information�and�comply�with�
instructions�can�result�in�PERSONAL�INJURY,�DEATH�AND/OR�
PROPERTY DAMAGE.
•� To�avoid�electrical�shock�or�damage�to�equipment,�disconnect�
power�before�installing�or�servicing�and�use�only�wiring�with�
insulation�rated�for�full�device�operating�voltage.
•� To�avoid�potential�fire�and/or�explosion�do�not�use�in�potentially�
flammable�or�explosive�atmospheres.
•� Retain�these�instructions�for�future�reference.
•� This�product,�when�installed,�will�be�part�of�an�engineered�
system�whose�specifications�and�performance�characteristics�
are�not�designed�or�controlled�by�HK�Instruments.�Review�
applications�and�national�and�local�codes�to�assure�that�the�
installation�will�be�functional�and�safe.�Use�only�experienced�and�
knowledgeable�technicians�to�install�this�device.
SPECIFICATIONS
Thank� you� for� choosing� an� HK� Instruments� RHT-MOD� Duct� se-
ries�relative�humidity�transmitter�with�Modbus�interface.�The�RHT�
-MOD�Duct�series�is�intended�for�use�in�commercial�environments�
in�HVAC/R�applications.
RHT-MOD�Duct�is�a�relative�humidity�transmitter�with�temperature�
output�installed�in�air�ventilation�duct.�In�addition�to�these�measured�
values,�RHT-MOD�Duct�calculates�various�parameters�such�as�dew�
point,�mixing�ratio,�enthalpy�and�absolute�humidity.�Illuminated�dis-
play�ensures�easy�readability�also�from�a�distance.�The�RHT-MOD�
Duct�has�a�screwless�lid�and�an�easily�adjustable�mounting�flange�
that�make�the�installation�of�the�device�easy.
RHT-MOD� Duct� series� devices� are� commonly� used� to� monitor� and�
control:
•��Relative�humidity�and�temperature�levels�of�incoming�and�return�air�
in�ventilation�system
SPECIFICATIONS
Performance
Measurement ranges:
Temperature:�-30...80�°C,�sensor
Relative�humidity:�0–100�%
Accuracy:
Temperature:�<0.5�ºC
Relative�humidity:�±2...3�%�at�0...50�°C�and�10–90�%�rH
Total�error�band�includes�accuracy,�hysteresis�and
temperature�effect�over�5...50�°C�and�10–90%�rH.
Technical Specifications
Media compatibility:
Dry�air�or�non-aggressive�gases
Measuring units:
°C�and�%�rH
Measuring element:
Temperature:�NTC10k
Relative�humidity:�Thermoset�polymer�capacitive
sensing�element
Environment:
Operating�temperature:�0...50�°C
Storage�temperature:�-20...70�°C
Humidity:�0�to�95�%�rH,�non�condensing
Physical
Dimensions:
Case:�119�x�95.5�x�45�mm
Probe:�L=188�mm,�d=12�mm
Mounting:
With�flange,�adjustable�40...155�mm
Weight:
150�g
Materials:
Case:�ABS
Cover:�PC
Probe:�ABS
Mounting�flange:�LLPDP
Protection standard:
IP54
Electrical connections:
�
4�spring�loaded�terminals
Power�supply:�
�
(24�V�and�GND)
�
0.2–1.5�mm2�(16–24�AWG)
Modbus�RTU:�
�
A�and�B�line
�
0.2–1.5�mm2�(16–24�AWG)
Electrical
Supply�voltage:�24�VAC�or�VDC�±10�%
Current�consumption:�max�90�mA�(at�24�V)�+�10�mA�for�
each�voltage�output
Communication
Protocol:�MODBUS�over�Serial�Line
Transmission�Mode:�RTU
Interface:�RS485
Byte�format�(11�bits)�in�RTU�mode:
�
Coding�System:�8-bit�binary
�
Bits�per�Byte:
�
�
1�start�bit
�
�
8�data�bits,�least�significant�bit�sent��
�
�
first
�
�
1�bit�for�parity
�
�
1�stop�bit
Baud�rate:�selectable�in�configuration
Modbus�address:�1−247�addresses�selectable�in
configuration�menu
Conformance
Meets�the�requirements�for:
�
�
CE:�
�
UKCA:
EMC:�
�
2014/30/EU�
S.I.�2016/1091
RoHS:�
�
2011/65/EU�
S.I.�2012/3032
WEEE:�
�
2012/19/EU�
S.I.�2013/3113
INTRODUCTION
WARNING
APPLICATIONS
RoHS
COMPLIANT
Copyright HK Instruments 2021
www.hkinstruments.fi
Installation version 7.0 2021
Tighten the
screw
SCHEMATICS
DIMENSIONAL DRAWINGS
INSTALLATION
STEP 1: MOUNTING THE DEVICE
1)�Mount�the�device�in�the�desired�location�(see�step�1).
2)�Route�the�cables�and�connect�the�wires�(see�step�2).
3)�The�device�is�now�ready�for�configuration.
�WARNING!�Apply�power�only�after�the�device�is�properly�wired.
1)�Select�the�mounting�location�(on�a�duct).
2)�Use�the�mounting�flange�of�the�device�as�a�template�and�mark�the�
screw�holes.
3)�Mount�the�flange�on�the�duct�with�screws�(not�included).�(Figure�1a)
4)�Adjust�the�probe�to�the�desired�depth.�Ensure�that�the�end�of�the�
probe�reaches�the�middle�of�the�duct.�(Figure�1b)
5)�Tighten�the�screw�on�the�flange�to�hold�the�probe�in�position.
Figure 1a - Mounting a flange
Figure 1b - Mounting the probe in a flange
Air flow direction
Air flow direction
Air flow direction
Air flow direction
Air flow direction
Strain relief facing down
Figure 1c - Mounting orientation
Display connection
Terminal block
A
B
24 V
GND
Joystick 1
Joystick 2
Joystick 3
Select
Up
Down
Menu buttons
95.5
88.5
45.0
188.0
Copyright HK Instruments 2021
www.hkinstruments.fi
Installation version 7.0 2021
STEP 3: CONFIGURATION
For�CE�compliance�a�properly�grounded�shielding�cable�is
required.
1)�Unscrew�the�strain�relief�and�route�the�cable(s).�
2)�Connect�the�wires�as�shown�in�figure�2a.
3)�Tighten�the�strain�relief.
A
24 V
GND
+
Power Supply
24VDC / 24VAC
Modbus A
Modbus B
B
1)�Activate�the�device�Menu�by�pushing�the�the�select�button�for�2�
seconds.�
8)�Select�temperature�offset:�+-5�°C.
Function�04�-�Read�input�register
Register
Parameter description
Data Type
Value
Range
3x0001
Program�version
16�bit
0...1000
0.0...99.00
3x0003
rH�reading
16�bit
0...1000
0.0...100.0�%
3x0004
Temp.�reading
16�bit
-300...800
-30.0...80.0�°C
3x0006
RH�Offset
16�bit
-100...100
-10.0...10.0�%�rH
3x0007
TE�Offset
16�bit
-50...50
-5.0...5.0�°C
3x0008
Dew�point
16�bit
-300...800
-30.0...80.0�°C
3x0009
Absolute�humidity
16�bit
0...800
0.0...80.0�g/m³
3x0010
Enthalpy
16�bit
0...850
0.0...85.0�kJ/kg
3x0011
Mixing�ratio
16�bit
0...800
0.0...80.0�g/kg
STEP 2: WIRING DIAGRAMS
Figure 2 - Wiring diagram
ADDRESS
1
SELECT
UP
DOWN
5)�Select�the�baud�rate:�9600/19200/38400/57600.
BAUD RATE
9600
SELECT
UP
DOWN
6)�Select�the�parity�bit:�None/Even/Odd.
PARITY BIT
NONE
SELECT
UP
DOWN
�7)�Select�humidity�offset:�+-10�%�rH,�Offset�feature�enables�field�
calibration.�This�is�necessary�in�demanding�applications�requiring�
annual�calibration.���
RH OFFSET
0.0 %RH
SELECT
UP
DOWN
TE OFFSET
0.0 °C
SELECT
UP
DOWN
9)�Push�the�select�button�to�exit�menu.
SELECT
EXIT MENU
SELECT
4)�Select�the�address�for�Modbus:�1...247.
Configuration�of�the�RHT-MOD�Duct�series�device�consists�of�
configuration�menu�options�(display�versions�only).
Press�the�select�button�to�accept�changes.�Move�to�the�next�setting�
by�pressing�the�down�button.�Select�the�exit�menu�to�save�the�
settings.�If�the�buttons�are�unused�for�3�minutes,�the�basic�view�will�
reappear�automatically,�and�the�changed�settings�are�not�saved.
2)�Select�the�value�shown�on�the�display�row�1.
� (temperature�/�dew�point�/�mixing�ratio�/�enthalpy�/
� absolute�humidity�/�relative�humidity)
DISPLAY ROW1
DEW POINT
SELECT
UP
DOWN
3)�Select�the�value�shown�on�the�display�row�2.
� (temperature�/�dew�point�/�mixing�ratio�/�enthalpy�/
� absolute�humidity�/�relative�humidity)
SELECT
UP
DOWN
DISPLAY ROW2
ENTHALPY
Function�03�-�Read�input�holding�register
Register
Parameter description
Data Type
Value
Range
4x0002
RH�Offset
16�bit
-100...100
-10.0...10.0�%�rH
4x0003
TE�Offset
16�bit
-50...50
-5.0...5.0�°C
STEP 4: MODBUS REGISTERS
CONFIGURATION continued
Copyright HK Instruments 2021
www.hkinstruments.fi
Installation version 7.0 2021
WARRANTY POLICY
The�seller�is�obligated�to�provide�a�warranty�of�five�years�for�the�de-
livered� goods� regarding� material� and� manufacturing.� The� warranty�
period�is�considered�to�start�on�the�delivery�date�of�the�product.�If�a�
defect�in�raw�materials�or�a�production�flaw�is�found,�the�seller�is�ob-
ligated,�when�the�product�is�sent�to�the�seller�without�delay�or�before�
expiration�of�the�warranty,�to�amend�the�mistake�at�his/her�discre-
tion�either�by�repairing�the�defective�product�or�by�delivering�free�of�
charge�to�the�buyer�a�new�flawless�product�and�sending�it�to�the�buyer.�
Delivery�costs�for�the�repair�under�warranty�will�be�paid�by�the�buyer�
and�the�return�costs�by�the�seller.�The�warranty�does�not�comprise�
damages�caused�by�accident,�lightning,�flood�or�other�natural�phenom-
enon,�normal�wear�and�tear,�improper�or�careless�handling,�abnormal�
use,�overloading,�improper�storage,�incorrect�care�or�reconstruction,�
or�changes�and�installation�work�not�done�by�the�seller.�The�selection�
of�materials�for�devices�prone�to�corrosion�is�the�buyer’s�responsibil-
ity,�unless�otherwise�is�legally�agreed�upon.�Should�the�manufacturer�
alter�the�structure�of�the�device,�the�seller�is�not�obligated�to�make�
comparable� changes� to� devices� already� purchased.� Appealing� for�
warranty�requires�that�the�buyer�has�correctly�fulfilled�his/her�duties�
arisen�from�the�delivery�and�stated�in�the�contract.�The�seller�will�give�
a�new�warranty�for�goods�that�have�been�replaced�or�repaired�within�
the�warranty,�however�only�to�the�expiration�of�the�original�product’s�
warranty�time.�The�warranty�includes�the�repair�of�a�defective�part�
or�device,�or�if�needed,�a�new�part�or�device,�but�not�installation�or�
exchange�costs.�Under�no�circumstance�is�the�seller�liable�for�damages�
compensation�for�indirect�damage.
RECYCLING/DISPOSAL
The� parts� left� over� from� installation� should� be�
recycled� according� to� your� local� instructions.�
Decommissioned� devices� should� be� taken� to� a�
recycling�site�that�specializes�in�electronic�waste.