You could use relays to switch each thermocouple in turn to one thermocouple amplifier. This will introduce cold-end error due to the metal missmatch at the thermocouple connections. You can either choose to ignore the error (20degC or so) or it can be compensated for by having and RTD measure ambient temperature, which is then subtracted from the measured temperature.
jackrae:
You could use relays to switch each thermocouple in turn to one thermocouple amplifier. This will introduce cold-end error due to the metal missmatch at the thermocouple connections. You can either choose to ignore the error (20degC or so) or it can be compensated for by having and RTD measure ambient temperature, which is then subtracted from the measured temperature.
If you place the relays close to the thermocouple interface IC the ambient temperature at that point should be the same and so the compensation performed by the TC interface chip should still be valid. Only if the relays are placed externally and are at different ambient temperature then the TC interface chip is at would there be a compensation problem.
With no cold junction compensation you should not get more than ~10C error according to that AD-369 datasheet, but that is including ambient temperatures well outside of human comfort.
For now my research end up with MAX6675 setup.
There is also simple tutorial: MAX6675 Thermocouple - Cookbook | Mbed.
It costs about 3.23$ per peace so this is cheaper than relay + transistor for each thermometer. 8)
FYI, MAX6675 has been replaced by MAX31855, which has wider temperature sensing range, better resolution, and is available in versions for several different thermocouple types. Still has an SPI interface, but the data format is changed from the MAX6675, so libraries for the earlier part will not work for the MAX31855.
LeXLuther422:
I made a break out board for the MAX31855 chip because I wanted to play with that chip too.
I have the bare board up on lish.com with the caps inductors and protector. https://dcande.lish.com/
This is almost same situation - financially disadvantageous for me:
8$ Your product + MAX31855 + shipping and I need at least 6 or 8 sets of these.
Come on guys! Do You would buy 6-8 thermometer for 120$+ ?