Bob J. wrote:

> Good catch Sphero!  I did not realize that an offset voltage was coming from
> the T+ lead until after reviewing the block diagram of the 6675.  

This is the problem with such integrated devices. Traditionally, you'd have
the thermocouple break detection (and maybe some amplification) before the
mux. With this all-in-one device, you can't easily separate this from the
rest.

Using it with 16 thermocouple inputs, it seems you're working against the
design of this device (unless you use 16 of them). Use a traditional ESD
protection and break detection on each input, add possibly a differential
amplifier for each input (alternatively only one after the mux), mux that
into an ADC, add a simple cold junction temperature sensor and do the
compensation and linearisation in firmware. This sounds like a lot of
stuff, but it's probably easier than trying to multiplex such an active
input that wasn't designed to be multiplexed.

Gerhard

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