198 Rockwell Automation Publication 1769-UM021I-EN-P - May 2018
Chapter 8 Use I/O Modules with CompactLogix 5370 L2 Controllers
Cold Junction Compensation Update Times
You must account for more voltage at the junction of the thermocouple field
wires and the input point. This condition applies when you use any of the
thermocouple input types on your embedded analog input. More voltage can
alter the input signal on that point and, therefore, affect the update time of that
channel.
The process to account for increased voltage at an input point by using a
thermocouple type input is cold junction compensation (CJC). You enable
CJC for a given channel on the Input Configuration tab of the Module
Configuration dialog box, as shown in the following graphic.
By default, CJC is disabled. You must clear the Disable Cold Junction
Compensation checkbox to use CJC for a given channel.
You are not required to enable CJC for a channel by using the thermocouple
input type. If you enable CJC and select Update Cold Junction Compensation
every other scan, an extra update time exists on the channel. This extra update
time increases the overall channel update time.
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