Is there a way to test a thermocouple?

[BottleFed70]

My PID temp controller says "EEEE" where it normally displays the current temp.

I've removed the thermocouple, re-connected it outside of the oven, and double-checked all of the connections, but it still doesn't work. I'm convinced the problem is either with the controller or the thermocouple.

Is there a way to test if a thermocouple is working properly? It's a "k-type", unfortunately I don't have a spare one I can test with.

[jabe421]

The easiest way to check a k-type thermocouple is to measure the voltage output with a DVM or DMM. A k-type thermocouple will output roughly 40uV per degree C and a flame from a candle or bic style lighter will burn at about 1000°C. When you connect your thermocouple to the DMM at room temperature you should have about 0v, when the thermocouple tip goes into the lighter flame you will have about 40mV.

40uV/°C * 1000°C = 40mV

Now depending on the type of probe you have on the end of your thermocouple you may not be able to get it up to the full 1000°C so your voltage my fluctuate between 35mV and 40mV.

This is some thermocouple testing data from Omega, it will probably give you more information that you will even want to know about thermocouples and the differences between them. If you want more information just let me know.

http://www.omega.com/temperature/Z/pdf/z021-032.pdf

[PhredAre]

Great post, who says we can't learn something new every day, thanks. Fred

[FigureLLC]

Originally Posted by PhredAre

Great post, who says we can't learn something new every day, thanks. Fred

yeah, i just committed this to memory. thanks!

[BottleFed70]

So I tested my thermocouple today, and it seems to work.

When cold, my DMM read 0.4 millivolts.
When I started to heat it, I watched the voltage quickly climb to 20+ millivolts.

So then I connected it back up to the temp controller and suddenly the controller was reading temperature as normal(although too high as the TC was still warm).

This got me thinking... I keep my oven outside in a covered area. It's been getting DAMN cold up here in Canada the last week. Since my DMM could barely read any voltage when cold (and this is after it was heated a little by me handling it), I got to thinking that maybe the cheapy $30 Ebay temp controller might also have a hard time reading such a low voltage when it's so cold.

So basically, my new theory is that the oven was simply too cold and the temp controller was not able to properly read that low of a temp (out of range). If It happens again, I'll try heating the thermocouple in the oven a little and we'll see if it starts working.

Thanks for the testing info jabe421

[CarWiz]

Operating conditions for most of PIDs are 0-50°C (32-122°F) with humidity ≤ 85%. With the recent conditions, even down here, you might be outside that range. The k-type TCs should be able to read around -200 to 1300°C (-328 to 2372°F)

Also, you might have a loose connector or broken lead on the TC. I've gotten the "EEEE" when my TC wasn't connected. It means one of the parameters/values is out of range. In this case, the input. But I wouldn't even power the unit up when it's outside the above temperature range. You could damage the unit.