I'm working on a project, which is focused on taking frequent (250ms interval or smaller) measurements of extreme temperatures (0-700 C) in 16 points. I need to take measurements of multiple thermocouples, and I'm having trouble deciding on the best approach.
One of my ideas was to use 16 thermocouple amplifier ICs that are I2C enabled, putting all of them on a PCB with STM32F4 and taking measurements every 250ms. However, most thermocouple amplifier ICs like MCP96RL00 allow for only 8 devices per bus, which creates the need to use two I2C buses for 16 thermocouples.
Then, I was thinking of using a single, good thermocouple amplifier IC, with cold junction compensation and all the fancy features, connecting all thermocouple negative terminals to a common piece of copper on a PCB and using a ultiplexer to switch between which thermocouple's positive terminal goes to the IC. However, I have very poor experience with analog electronics, and I'm not sure if there even exists a multiplexer, that allows voltages as small as those of thermocouples (milivolts), has low resistance, and has 16 channels. I wasn't able to find one such device.
Electromechanical relays could do the job, but they might be too slow for going through 16 or more thermocouples every 250ms.
How to approach this problem? Is any of my ideas viable? Would you suggest something more optimal? If the multiplexer way is viable, can someone point me in the right direction of a multiplexer, which can be used this way? I don't need extreme precision - 2-5 degrees Celsius of precision would be acceptable. Worst-case scenario, 16 MCP96RL00 will do the job, but I'd like to optimize the costs wherever possible, to stay within the budget - it's a student project with a very tight one. In case of expanding to 64 or 128 thermocouples, the costs get insane.