What is the Effect of Temperature on OHM (resistance) test?

[JRKH]

Got a quick question for the electrical types.

We are going to have to test parts for resistance.
We need to have 25 megaohms at 2500 vdc.
Parts are composed of 2 steel parts 3/4 inch dia seperated by about 7/16 inch of G-10 fiberglass and epoxy resin.

Now much effect would a 20 degree F drop in temperature have on the resisitance reading?
Any Ideas?

Thanks

James

 

[Al Rosen]

Got a quick question for the electrical types.

We are going to have to test parts for resistance.
We need to have 25 megaohms at 2500 vdc.
Parts are composed of 2 steel parts 3/4 inch dia seperated by about 7/16 inch of G-10 fiberglass and epoxy resin.

Now much effect would a 20 degree F drop in temperature have on the resisitance reading?
Any Ideas?

Thanks

James

Off the top of my head, negligible. The G10 is an insulator and without looking at the spec sheet for the G10 I believe that you should have more than 25 meg. You didn't mention the temperature, which can make a difference. I will look up the spec sheet on G10 and let you know more details on what to expect.

 

[JRKH]

Test temp

Off the top of my head, negligible. The G10 is an insulator and without looking at the spec sheet for the G10 I believe that you should have more than 25 meg. You didn't mention the temperature, which can make a difference. I will look up the spec sheet on G10 and let you know more details on what to expect.

Thanks Al,
The temp I'm looking at would be between say, 70 and 50 dg F.
I rather expect that it won't be an issue, but since the customer instructions are so vague (they give no time or temp indicators for the test) I wanted to be sure not to over-engineer the test (one of my vices).

James

 

[Al Rosen]

James, the volume resistivity is somewhere in the range of 10^12 to 10^14 ohm-cm (1 cm cube) and has an inverse temp coefficient. So your resistance should go up as the temp drops and you should find that you are >> 25 Mohm.

 

[JRKH]

Thanks Al

James, the volume resistivity is somewhere in the range of 10^12 to 10^14 ohm-cm (1 cm cube) and has an inverse temp coefficient. So your resistance should go up as the temp drops and you should find that you are >> 25 Mohm.

Al,
Thanks.
That is the opposite of what I had been thinking based on my brief research. I'm glad I asked.

James.

 

[Tim Folkerts]

Al,
Thanks.
That is the opposite of what I had been thinking based on my brief research. I'm glad I asked.

James.

Yep.

Insulators & semiconductors generally increase in resistivity when they get cooler, but metals decrease. Perhaps you had been thinking of metals.

Tim

 

[JRKH]

Very possible

Yep.

Insulators & semiconductors generally increase in resistivity when they get cooler, but metals decrease. Perhaps you had been thinking of metals.

Tim

I get to plead stupid when it comes to this kind of stuff. My background is mechanical and that's where my feel is. I don't know much about those little electron guys except I don't like to touch them, my hair is curly enough.

James