Emerson SL-31080 User Manual

T

EMPERATURE

/H

UMIDITY

 T

RANSMITTER

 - W

ALL

 (4-20 

M

A)

The THW420 combination 

temperature/humidity transmitter 

is designed to meet applications 

that require local indication of both 

temperature and humidity in a 

single, aesthetically pleasing 

enclosure. 
This device incorporates a 10K ohm 

(Ω) platinum RTD. 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.

The 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 three-

wire termination. In most cases, it obtains power 

from the analog input to which it is connected and 

no external power is required.

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 induc-

tive loads such as motors, generators and coils. Lie-

bert also recommends making power connections 

with twisted pair wire of at least 22 AWG and crimp-

type connectors.

Output

4 to 20 mA

Sensor

10K 

Ω platinum RTD

Supply Voltage

24 VDC

Tolerance of Resistance
(Accuracy)

±1.5°F (±0.83°C)
±2% RH (from 15 to 95% RH)

Response Time

20 seconds for a 63% step

Environmental Operating
Range (Transmitter)

45°F to 96°F; 0 to 100% RH
(7°C to 35°C); 0 to 100% RH

Liebert recommends wiring the sensor 

WITHOUT power applied because 

accidental arcing may damage the product 

and will void the warranty.

U3

SW2 OUTPUT SELECT

ON

0-5V

0-5V

0-5V

CAL

RUN

RESIST.

4-20ma

4-20ma

SW2

C9

Gn

d

V+

Ch1

Ch2

J2

J3

DISPLAY CYCLE 

IN SECONDS

10

3
T

POT1

20
H

Ch
3

CA
L

Te

m

p

Te

m

p

R1
9

T&B

SWITCH

Short

Norm

Open

SW1

RTH1 RTH2

J1

%RH

Ch3

Ch2

Ch1

Building Automation

Products, Inc.

Copyright 2000

REV. 101600

XCOMBO T&B

4-20 mA

Input #1

Ground

4-20 mA

Input #2

+
-

+
-

To GND (common) 

of controller*

From +24VDC 

of controller or 

power supply

To controller’s 

analog input 

(humidity signal,

4-20mA)

To controller’s 

analog input

(temperature signal,

4-20mA)

THW420

Combination Temperature/Humidity Transmitter Wall 4-20 mA @ 45°F to 96°F and 0 to 100% RH