Rockwell Automation 1756-OF8I ControlLogix Eight-channel Isolated Analog I/O Modules - Manual (Page 83)

Rockwell Automation Publication 1756-UM540A-EN-P - May 2014 83
1756-IRT8I Combined Temperature-sensing Isolated Analog Module Chapter 4
The thermoelectric effect alters the input signal and must be compensated for to
measure temperatures accurately. To accurately compensate the input signal from
your module, you must use a cold junction compensation (CJC) sensor to
account for the increased voltage.
Remember the following when compensating the input signal from your module:
• Cold junction compensation is optional and can be disabled.
• The 1756-IRT8I module uses two channels for cold junction
compensation. When using an RTB, you must connected CJC sensors at
RTB terminals 1 and 2 and 35 and 36.
• Differences exist between using an RTB or IFM to connect wiring to the
module. They are described in the rest of this section.
IMPORTANT CJC sensors are only required with use of the Thermocouple input type and
when channel wiring is connected via an RTB.
If you are using an IFM to connecting wiring to a channel using the
Thermocouple input type, you do not need to use CJC sensors.
CJC sensors do not come with the 1756-IRT8I module. You must order CJC
sensors, product catalog number 1756-CJC, separately from the 1756-IRT8I
module for CJC sensors which attach directly to the module's screw terminals.
Catalog number 1756-CJC includes two CJC sensors.
To order CJC sensors, contact your local Allen-Bradley distributor or Rockwell
Automation sales representative.
IMPORTANT If you use cold junction compensation, you must connect CJC sensors to
both channels, that is, terminals 1, 2, 35, and 36.
You cannot use cold junction compensation and connect a CJC sensor
to only one channel.