temperature/humidity transmitter - wall (4-20 ma)

TEMPERATURE /HUMIDITY TRANSMITTER - WALL (4-20 MA)
Description
Termination
The Liebert THW420 combination
temperature/humidity transmitter
is designed to meet applications
that require local sensing of both
temperature and humidity in a
single, aesthetically pleasing
enclosure.
The Liebert THW420 transmitter must be powered
from a 24 VDC supply. The combination
temperature/humidity sensor is terminated as
follows:
• The humidity transmitter requires a three-wire
termination for the 4-20mA output using 24 VDC.
• The temperature sensor also requires a threewire termination. In most cases, it obtains power
from the analog input to which it is connected and
no external power is required.
This device incorporates a digital
solid state temperature and
capacitive humidity sensor. The transmitter
requires 24 VDC. The sensor provides an
accurate and predictable four-wire, 4-20 mA
output signal for temperature and a second
4-20 mA output signal for humidity.
Dimensions
2.86"
(72.7mm)
1.06"
(26.9mm)
Though interference from external sources is not a
major problem with current transmitters, Liebert
recommends separating the wiring from line voltage
wiring and from wiring used to supply highly
inductive loads such as motors, generators and coils.
Emerson Network Power also recommends making
power connections with twisted pair wire of at least
22 AWG and crimp-type connectors.
Controller
To GND (common) of controller*
From +24VDC of
controller or power
supply
Front
To controller’s
analog input
(temperature signal,
4-20mA)
Wall
To controller’s
analog input
(humidity signal,
4-20mA)
4.5"
(114.3mm)
Ground
4-20 mA
Input #1
+
4-20 mA
Input #2
+
-
* NOTE:
The GND (common)
terminal is common
between the Power
and Sensor
Side
Front
+24VDC should be
used at all times
Specifications
Output
Sensor
Supply Voltage
Tolerance of Resistance
(Accuracy)
Response Time
Environmental Operating
Range (Transmitter)
4 to 20 mA
Temperature - Band gap
semiconductor
Humidity - Capacitive
24 VDC
±1.2°F (±0.6°C)
±2% RH (from 15 to 95% RH)
8 seconds for a 63% step
45°F to 96°F; 0 to 100% RH
(7°C to 35°C); 0 to 100% RH
SL-31080 Product Specification/Installation Sheet
Terminations
Notice
Risk of accidental electric arc. Can cause equipment
damage. Emerson recommends wiring the sensor
WITHOUT power applied; accidental arcing may
damage the product and will void the warranty.
page 1
03/12 (Rev. 1)
Enclosure Mounting Instructions
Ordering Information
Qty
Part #
THW420
Mounting hardware is provided for both junction box
and drywall installation.
Description
Combination Temperature/Humidity
Transmitter Wall 4-20 mA @ 45°F to
96°F and 0 to 100% RH
1. Pull the wires through the opening in the base
plate.
Mounting
2. For junction box installation: Secure the
base to the box using the #6-32 x 1/2" mounting
screws provided.
Wall
For drywall installation: Drill two 3/16" holes
3-1/4" apart on center. Insert the drywall
anchors and secure the base using the #6 x 1"
sheet metal screws provided.
Junction box
2" x 4"
3. Terminate the unit according to the guidelines
in Termination on page 1.
4. Attach the cover by latching it to the top of the
base, rotating the cover down and snapping it
into place.
5. Secure the cover by backing out the lock-down
screws using a 1/16" allen wrench until they are
flush with the bottom of the cover.
Troubleshooting - Humidity Signal
Verification, 4 to 20 mA Signal
Mounting
screws
Cover Locking Screws
1/16" Allen
NOTE
In a wall-mount application, the wall
temperature and the temperature of the air
within the wall cavity can cause erroneous
readings. The mixing of room air and air
from within the wall cavity can lead to
condensation and premature failure of the
sensor.
To prevent these conditions, seal the conduit
leading to the junction box and seal the hole
in the drywall by using an adhesive backed,
foam insulating pad.
You will measure the humidity output by placing an
ammeter in series with the controller input. The
controller input is connected to the terminal marked
“Ch1 or Ch2” on the humidity board.
1. Verify the unit is terminated properly using
Figure 4 shown below, and set your meter to
the “Volts” setting.
2. Verify you have 24 VDC supplied to the unit by
measuring between the “V+” and “GND”
terminals at the sensor, as shown below in
Figure 3.
3. Set your meter to “Amps” and measure the
output between “Ch1 or Ch2” and the controller
input as shown below in Figure 3.
4. Use the following formula to determine what
humidity the sensor is reading:
(mA - 4) / 0.16 = %RH
where mA is the current reading from the
ammeter (in mA)
Example:
If the current reading is 16 mA, then:
%RH = (16 - 4) / 0.16
= 12 / 0.16
= 75%
SL-31080 Product Specification/Installation Sheet
page 2
03/12 (Rev. 1)
Figure 1 Supply Voltage and 4-20mA Verification
GND(-)
Figure 2 4 to 20 mA Output Connection
GND(-)
GND(-)
POWER SUPPLY
CONTROLLER
+
V+
+
V
V+
A
-
GND(-)
POWER SUPPLY
Analog Input
CONTROLLER
V+
Analog Input
-
Ch1 or
Ch2
V+
ROOM SENSOR
Ch1 or
Ch2
ROOM SENSOR
Troubleshooting Guide
The following table lists common problems and possible solutions. For more information, consult your local
dealer, Liebert representative or the Liebert Worldwide Support Group.
Problems
Possible Solutions
Unit will not operate
• Check +24 VDC power supply at controller.
• Disconnect the sensor and check power wires for +24 VDC.
Humidity reading is maximum
20 mA or 100%
• Make sure the sensor is wired properly.
Humidity reading is minimum
4 mA or 0%
• Verify that the humidity sensor is wired properly.
Humidity reading in software
appears to be off more than
specified accuracy
• Check all software parameters.
• If available, check the sensor against a calibrated control such as a hygrometer.
• Determine if the sensor is exposed to an external source more than room.
Temperature sensor in frontend software is reading high
• Make sure wiring is correct.
• Disconnect wires and measure with a multimeter.
Temperature sensor in frontend software is reading low
• Make sure wiring is correct.
• Disconnect wires and measure with a multimeter.
SL-31080 Product Specification/Installation Sheet
page 3
03/12 (Rev. 1)
Troubleshooting - Humidity Signal Verification
4 to 20 mA Signal
You will measure the humidity output by placing an ammeter in series with the controller input. The
controller input is connected to the terminal marked “Ch1 or Ch2” on the humidity board.
1. Verify the unit is terminated properly using Figure 4 shown below, and set your meter to the “Volts”
setting.
2. Verify you have 24 VDC supplied to the unit by measuring between the “V+” and “GND” terminals at the
sensor, as shown below in Figure 3.
3. Set your meter to “Amps” and measure the output between “Ch1 or Ch2” and the controller input as
shown below in Figure 3.
4. Use the following formula to determine what humidity the sensor is reading:
(mA - 4) / 0.16 = %RH
where mA is the current reading from the ammeter (in mA)
Example:
If the current reading is 16 mA, then:
%RH = (16 - 4) / 0.16
= 12 / 0.16
= 75%
Figure 3 Supply Voltage and 4-20mA Verification
GND(-)
Figure 4 4 to 20 mA Output Connection
GND(-)
POWER SUPPLY
CONTROLLER
+
V+
+
V+
V
A
-
GND(-)
GND(-)
POWER SUPPLY
Analog Input
CONTROLLER
V+
Analog Input
-
Ch1 or
Ch2
V+
ROOM SENSOR
SL-31080 Product Specification/Installation Sheet
Ch1 or
Ch2
ROOM SENSOR
page 4
03/12 (Rev. 1)