A-B 1746-NT8 SLC500 Thermocouple/mV Analog Input Module ​Module Operation

If open circuit detection is enabled, the module tests for an open-circuit

condition. If it detects an open-circuit, over-range, or under-range

condition, the module sets a unique bit in the channel status word

and causes the channel status LED to flash.

The SLC processor reads the converted thermocouple or millivolt data

from the module at the end of the program scan, or when

commanded by the ladder program. After the processor and module

determine that the data transfer was made without error, the data can

be used in your ladder program.

Module Operation

The module’s input circuitry consists of eight differential analog

inputs, multiplexed into an A/D convertor. The A/D convertor reads

the analog input signals and converts them to a digital value. The

input circuitry also continuously samples the CJC sensors and

compensates for temperature changes at the cold junction (terminal block).

IMPORTANT When using multiple thermocouples, the potential

between any two channels cannot exceed the

channel-to-channel differential voltage (12.5 volts).

For more information, see Appendix B.