TEMPERATURE/HUMIDITY TRANSMITTER - WALL (4-20
M
A)
Product Specification/Installation Guide
590-1616-501A\SL-31080_REV2_11-17
3
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)
TROUBLESHOOTING
- Humidity Signal Verification
TROUBLESHOOTING GUIDE
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 20 mA or
0%
• Verify that the humidity sensor is wired properly.
Humidity reading in software appears to
be off more than specified
• 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 front end software
is reading high
• Make sure wiring is correct.
• Disconnect wires and measure with a multimeter.
The following table lists common problems and possible solutions. For more information, consult your local
dealer, Liebert representative or the Liebert Worldwide Support Group.
Example:
If the current reading is
16 mA, then:
%RH = (16 - 4) / 0.16
= 12 / 0.16
= 75%
Figure 1
- Supply Voltage and 4-20mA Verification
Figure 2
- 4-20mA Output Connection
ORDERING INFORMATION
PART #
DESCRIPTION
THW420
Combination Temperature/Humidity Transmitter Wall 4-20 mA @ 45°F to 96°F
and 0 to 100% RH
