range on multimeter

[gk]

what range would i set my multimeter at and how would i test a thermocouplr

 

[ban-all-sheds]

Well, they output in the low mV range, certainly not more than 100mV.

But IIRC you can't test them with a multimeter as connecting one up to them creates another thermocouple...

 

[felix]

You can test a thermocouple on a meter. It's true that when you connect the thing up you create not one but two extra thermocouples in the circuit but these will remain at room temperature while the working one is heated to several hundred degrees. Use your lowest mV range.

 

[ban-all-sheds]

You can test a thermocouple on a meter. It's true that when you connect the thing up you create not one but two extra thermocouples in the circuit but these will remain at room temperature

Thought they were supposed to be at 0°C?

I guess the important questions are:

1) What temperatures are the thermocouple measuring, and where & why?

2) How important is it that it's accurate?

3) What are the potential consequences of it not working properly?

 

[felix]

Good point. I assumed that the question referred to the usual FFD thermocouple where accuracy is not important. If the thing is part of a digital thermometer then that's different.

 

[mapj1]

You will not get much signal at all - usually microvolts per degree. You don't say what you want to check - on ohms the thermocouple should read low impedance (few ohms max) if not it has burnt open.
To check it actually works as a thermocouple though requires you to heat it, while looking for microamps on the terminals. To avoid being fooled, you will have to be careful to avoid magnetic induction in the meter leads (twist them perhaps) and to keep the thermocouple wir to meter lead junctions at the same temperature (side by side, no draught.)
The 200mV range (the lowest on most DVMs) is only really gong to show soemthing if you wave a blowlamp near the couple.
However, some boiler thermocoples are really a series stack of couples, (a thermopile) and produce a good fraction of a volt.

Apart from the most basic 'is it dead' test, a side by side test with a known good one is a much better bet.
good luck M.

 

[uselessFCUK]

Some useless info

http://www.nphheaters.com/technical/thermo_letter.htm

http://www.industrysearch.com.au/features/thermocouple.asp

http://www.temperatureworld.com/shci.htm

http://www.windmill.co.uk/thermocouple.html

http://www.omega.com/thermocouples.html

http://www.howstuffworks.com