multiplexing thermocouples
alcuemar,
It can be done, but it's not easy. There are two problems you need to deal with:
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The voltage amplitude is low, so you need to amplify the signal to get decent resolution and accuracy from your A/D converter.
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You must provide cold junction compensation. This is required because the connection from the thermocouple and the copper of a printed wiring board form a thermocouple.
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The Analog Devices AD595 performs the cold junction compensation and gain functions in one chip. However, you need one for each channel.
Regards,
Kral