Rockwell Automation 1746-NT8 SLC 500 Thermocouple/mV Analog Input Module/ Instructions - Manual (Page 10)

10 SLC 500 Thermocouple/mV Analog Input Module
Publication 1746-IN015C-EN-P - July 2001
Cold Junction Compensation (CJC)
To obtain accurate readings from each of the channels, the cold-junction
temperature (temperature at the module’s terminal junction between the
thermocouple wire and the input channel) must be compensated for. Two cold
junction compensating sensors are integrated in the removable terminal block.
They must remain installed to retain accuracy.
Wiring Guidelines
Isolation
The 1746-NT8 module provides the following electrical isolation:
•
12.5V dc electrical isolation channel to channel
•
500V dc for 1 minute electrical isolation channel to chassis ground
•
500V dc for 1 minute electrical isolation channel to backplane
Care must be taken when choosing a thermocouple type and connecting it to the
1746-NT8 module from the environment being measured. If adequate precautions
are not taken for a given thermocouple type, the electrical isolation of the 1746-NT8
module may be compromised.
ATTENTION
!
Do not remove or loosen the cold junction compensating
temperature transducers located on the terminal block. Both
CJCs are critical to ensure accurate thermocouple input readings
at each channel. The module will not operate in thermocouple
mode if a CJC is not connected.
Failure to observe this precaution can cause unintended
equipment operation and damage.