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Megohm Meter to Test Weld
If the weld is closed will I get OL signal?

My company is in the process of producing MI Thermocouple I was told by another company that you can use a megohm meter to test the tip to see if there are any holes in the weld by dipping it in water then hooking one lead on the megohm meter to the shielding and the order to a lead on the thermocouple.

If the weld is closed am I suppose to get a OL signal?

to answer your question, you'll need to provide a dimensioned drawing(s) of the sensor, and materials used.

You are getting into manufacturing details, that cannot be answered without a thorough design review.

By Steve Myres on 18 August, 2018 - 4:50 pm

Sounds more like this is an isolated, ungrounded t/c design, and they're checking to make sure the junction isn't making contact with the sheath.

A water test would only catch "holes" large enough to prevent water tension or air bubble blockage interference.


>A water test would only catch "holes" large enough to
>prevent water tension or air bubble blockage interference.

D has a point. It might not be large enough hole to wet the insulation in a timely manner. I wonder if creating a vacuum around the tip in a tiny chamber monitored by a pressure transmitter would work "leak down test". I have seen helium used along with a mass spectrometer because the molecule is so small.

Water test would certainly be less expensive.

if that's the case you don't need water, a megohm meter would be adequate unless you had a voltage breakdown target you were trying to maintain.

>Sounds more like this is an isolated, ungrounded t/c
>design, and they're checking to make sure the junction isn't
>making contact with the sheath.

I think you are correct. why not try it by dipping one in water that you know is not welded properly. The dry insulator will be non conductive, pure water is non conductive but for some reason combine the two and they may conduct quite well.

BTW normal tap water is reasonably conductive, I have a table here that says "Water-New York City 70 microsiemns/cm" that is on the high side.