There are several different solution available for thermocouple amplification such as the MAX31856, AD8495, and LTC2983. Some of these support grounded thermocouples (AD8495) and some don't (MAX31856). This is not explicitly stated in the datasheets. How can I tell? My best guess is that I needs to look for a common-mode voltage rejection down to 0V. Is this correct?
Below is a picture of a "grounded thermocouple" configuration.
Typically you look for this (MAXIM part): -
Input Common-Mode Range 0.5 to 1.4 V
It doesn't go down to (or below) 0 volts hence it's no good for a ground connected TC.
The AD part says this: -
Input Voltage Range −VS – 0.2 to +VS – 1.6
And this would be suitable to go 0.2 volts below the negative rail on the chip.
And for the LT part it says a similar story: -
Common Mode Input Range –0.05 to VDD – 0.3
So you have: -
As the main phrases to look for when choosing a chip that can handle grounded TC inputs.
