Testing the Thermocouple Amp

[Dominick A]

Last night, I finished soldering the necessary components to test my thermocouple amp. My 9 volt battery was registering around 9.2V. After hooking it up to the board, I was getting a reading of 8.9-9.0v through the amp connections. The other test with shorting the inputs gave me .17V when I think I should have been seeing closer to .115V.

What should I be looking for to get the board showing more accurate outputs, or is this a reasonable variance?

Keep in mind, I'm new to soldering and circuits, but have everything I need to do the job and can follow instructions really well, or at least I think I can

 

[Steve_M]

Following https://github.com/CapnBry/HeaterMeter/wiki/Thermocouple-Amplifier-Testing

"Now short the two thermocouple input pins together with a piece of wire. The output should drop to room temperature (in Celsius) * 5mV or about 0.10V-0.15V. If the AD8495 is still warm from soldering, it will affect this reading slightly."

If you're seeing .17 then the TC amp is reading 29.4C ( 5 / .17 = 29.4 ) Did you wait some time before testing the amp after soldering it?

 

[Dominick A]

Yes - I soldered, then watched the 2 hour premier of SVU, then tested. I'll try again tonight. Room temp should have been 23C. Otherwise, could it be an issue with any of the solder joints? I am 99% sure I used the right components in the right spots.

 

[Bryan Mayland]

I would call it close enough for testing purposes. When I assemble them I just check that it is ~3.2V, pulling 0-2mA on the power supply, then short the pins and verify it drops to around ~0.2V and still pulling 0-2mA which indicates it is responding properly. Failure conditions are 0V output, output stays at ~3.2V with the pins shorted, or I've seen a couple go to ~2V.

I'd say your work passes. Great job if this is all new to you!