Rockwell Automation 1756-OF8I ControlLogix Eight-channel Isolated Analog I/O Modules - Manual (Page 81)

Rockwell Automation Publication 1756-UM540A-EN-P - May 2014 81
1756-IRT8I Combined Temperature-sensing Isolated Analog Module Chapter 4
Thermocouple Wire Length Compensation
Wires connecting a thermocouple to the 1756-IRT8I module have an intrinsic
resistance that can negatively impact the module’s accuracy. The wire length and
gauge are directly related to resistance level and, by extension, to impact on the
module accuracy. The longer the wire length, the greater the resistance, the
greater the possible negative impact on module accuracy.
To avoid increased module error resulting from increased resistance levels, the
1756-IRT8I module can automatically compensate for resistance levels and
maintain its accuracy. The module measures the wire resistance and actively
compensates for that resistance with each sample.
Synchronized Sampling
This feature lets you synchronize input sampling across inputs on multiple
modules in the same chassis, forcing those inputs to sample simultaneously
within approximately 20
μ
S of each other.
IMPORTANT This functionality works when thermocouple wiring is connected to the
module before the module is powered or power is cycled to the module.
Connect wiring to the module before applying or cycling module
power.
You can disable compensation by removing the wiring prior to a power cycle
and reconnecting the wiring later.
IMPORTANT Synchronized Sampling is not limited to input sample across inputs on the
same module types.
You can use Synchronized Sampling across inputs on 1756-IF8I modules and
1756-IRT8I modules in the same system.