Rockwell Automation 1756-OF8I ControlLogix Eight-channel Isolated Analog I/O Modules - Manual (Page 40)

40 Rockwell Automation Publication 1756-UM540A-EN-P - May 2014
Chapter 2 ControlLogix Isolated Analog I/O Module Features
RTD Error
Module error on the 1756-IRT8I module used with an RTD input is defined in
ohms. The error is calculated across the entire input range selected, not the
available range of a sensor used with the module. For example, if the 1…500
Ω
input range is used, the module error is calculated across 510 Ω
(actual range = 0…510 Ω ).
The error in ohms translates to temperature, but that translation varies because
the relationship is non-linear. The most effective way to check 1756-IRT8I
module error is to calculate the error in ohms and use that value in a linearization
table to check the temperature error.
If the module is calibrated at operating temperature and the operating
temperature remains relatively stable, calibration accuracy is better than 0.05% of
the full range. This 0.05% value is a worst case value. In other words, with the
1…500
Ω input range selected, the worst case module error is 0.255 Ω .
Finally, you must check an RTD linearization table to determine how the
temperature error of 0.510
Ω
translates.
For example, if the 1756-IRT8I has a 0.05% (or 0.255 Ω ) error and is at a
temperature of 0 °C (32 °F), the temperature error is ±0.65 °C (±1.17 °F) when
the Platinum 385 sensor type is used. This same error at a temperature of 200 °C
(392 °F) translates to a temperature error of ±0.69 °C (±1.26 °F).