Testing Thermistor(s) used in Electric Motors.

The Electrical Apparatus Service Association
states within their seminar program devoted to
Root Cause Failure Analysis, "Caution: Do not
test thermistors with an ohmmeter. An ohmmeter
can supply enough current to damage a thermistor."

A digital ohmmeter is also cautioned against
using to test a thermistor by the presented program.

Any knowledge out there that can shed myth from fact?
(Or fact from myth?)

Can you test a thermistor used in electric motor applications,
or are they replaced regardless of what any test reveals?

If you do indeed have first hand knowledge on this subject, it
would be helpful to have an authenticated "source" other than
a website URL. Is there anything "published" on the subject?

And of course, thanks! (On what you're willing to share.)

John

Hi John. Check out "Managing Motors" 2nd ed by Richard Nailen ISBN 0-943876-09-5, page 6-37:'

"Thermistors themselves can usually be checked simply by resistance measurement. Unless the manufacturer of the specific thermistor has approved it , however, don't use a conventional ohmmeter to do this. The semiconductors will safely pass only very small currents. Ohmmeter current alone may be high enough to damage the thermistor. Therefore, use a high-impedance instrument"

So I guess you can check them using the right instrument. Also check your meter manual to verify whether you should start on the highest resistance scale or lowest resistance scale to minimize current.

By the way, Nailen has about 5 pages on thermistors. One of my favorite books on motors.

This message has been edited. Last edited by: electricpete,

"Pete",

Thank you.. for exposing a little more light on a subject of "negligible" value.
The ISBN number for tracing the published work is also greatly valued.
You obviously have a wealth of knowledge "know how", and know how to organize it.

Thank you again for sharing.

I'm Using "It"!

John

Thanks for the kind words. They are not totally deserved, I assure you. But I enjoy sharing and learning on this board, and I'm glad I could help.