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Topic: Thermocouple Isolation - opto isolator? (Read 248 times) previous topic - next topic


Hi all,

I could only find one other post about this and the solution presented is not compatible for me. I am using 2 Adafruit MAX6675 thermocouple amplifiers to read temperatures in an electric cartridge heater heated mold. Unfortunately one of the cartridge heaters is leaking voltage into the mold because the tolerance for its embedding was too high and there is a small air gap. The electrified mold is then grounding through one of my thermocouples. For now I am just getting crazy unreliable temperatures from the thermocouple but I am afraid I will eventually fry my arduino or worse my computer. A better explanation of the issue (although with different components and no arduino) is HERE.

First, yes I know the best solution is to fix the leaking voltage, I am having a new mold CNC'd with the proper hole size for embedding the heaters, but this will take 6 weeks and I can not wait that long.

For now, I am looking for a solution to isolate the thermocouple from the arduino, I've read a bit about opto isolation and think it might work for this application. I am thinking about ordering the sparkfun opto isolator to isolate each MAX6675 from my arduino. Does any one know if this will work or done anything like that?

If that doesnt work, I was thinking of using a USB-USB Isolator and just using it inbetween the arduino and my computer, sure I might eventually fry the Arduino, but they are cheap enough and I want to use my mold...

Any advice is appreciated, Please don't be mean...


Nov 10, 2017, 05:16 pm Last Edit: Nov 10, 2017, 05:16 pm by jremington
Presumably your problem is AC line isolation, failure of which is an extremely dangerous situation.

Optoisolators might work, if fast enough, but you would still have to power the MAX6675 by an isolated power supply, like batteries.

In that case, you might run everything off of batteries, for example use a laptop not connected to the AC line. But you would potentially be risking your life by touching the laptop while grounded.

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