How could this circuit use one temperature sensor to do cold junction compensation (CJC) for 4 channels TC?

Document created by analog-archivist Employee on Feb 23, 2016
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How could this circuit use one temperature sensor to do cold junction
compensation (CJC) for 4 channels TC?

 

The ADT7310, ±0.5°C Accurate digital temperature sensor is used for
Cold-Junction-Compensation when CN0287 processing temperature measurement by
thermocouples. ADT7310 could only measure the temperature close to itself but
there are several things done on the circuit to minimize the temperature
difference between the 4 terminal blocks.
1. There is no power-starving part around ADT7310 that would generate
temperature gap big enough to effect the final system performance.
2. The ADT7310 is placed on the middle of the terminal sides. The temperature
at this position is very close to the averaging temperature.
3. There are Coppers in three layers of the PCB board stitching together by
vias and surrounding the ADT7310 and 4 terminal blocks. These three layer
coppers would make the PCB board near terminal blocks a good conductor of heat
that minimize the temperature gap between terminal blocks and ADT7310.

For the aspect out of board, the air temperature should be minimized during
measurement. Adding a plastic case to isolated internal and external
environment just like most of the quality product would be appreciated to
minimize the temperature gap and changing rate.

If there are different type of sensor connected to different channel, it’s
recommended to connect thermocouples on the two channels in the middle close to
the ADT7310.

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