Module Operation

The thermocouple module input circuitry consists of four differential

analog inputs multiplexed into a single analog-to-digital (A/D)

convertor. The mux circuitry also continuously samples the CJC A and

CJC B sensors and compensates for temperature changes at the cold

junction (terminal block). The figure on the following page shows a

block diagram for the analog input circuitry.

The A/D convertor reads the selected input signal and converts it to a

digital value. The multiplexer sequentially switches each input

channel to the module’s A/D convertor. Multiplexing provides an

economical means for a single A/D convertor to convert multiple

analog signals. However, it does affect the speed at which an input

signal can change and still be detected by the convertor.