Clamp on ohmmeter?

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hardworkingstiff

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Wilmington, NC
The man that works with me claimed to have used a clamp on ohm meter while doing PoCo pole inspections. I told him he must have been checking amps not ohms because they don't make a clamp on ohm meter. He was adamant that he was checking ohms.

Question: Has anyone ever seen a clamp on meter that read ohms w/out wires? (I can't understand how that might work).
 
zbang said:
Sounds like Snake Oil (and you're right, you can'd measure resistance by the field strength).
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Resistance on the secondary side of a transformer is 'reflected' on the primary side, meaning that you can measure a resistance _through_ a transformer.

You can certainly have a 'clamp on' transformer, where the core is split.

The ground resistance tester mentioned above is a transformer coupled resistance tester, where the primary is a bunch of turns around a split core built into the instrument, the 'secondary' is the conductor that you clamp around, and the core is the clamp itself.

-Jon
 
We have Ideal meters at the shop that will read clamp-on hz. Comes in handy on our generator checks. Only works under load though. :mad: With no load you still have to use your leads.
 
The OP didn't mention that it was a ground resistance tester, only that it measures ohms (although I'm sure it was obvious to some people), and I still maintain that you can't measure resistance unless you know another term of the equation. With a classic ohmmeter, the meter knows the applied voltage/current, so it can figure out the resistance. It looks like the AEMC ground resistance tester supplies the test voltage through another coil of the clamp-on and uses these to derive the resistance measurement.

I would still not call this an ohmmeter, just as i wouldn't call a wiggy a voltmeter.
 
zbang said:
It looks like the AEMC ground resistance tester supplies the test voltage through another coil of the clamp-on and uses these to derive the resistance measurement.
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That is correct.
 
zbang said:
It looks like the AEMC ground resistance tester supplies the test voltage through another coil of the clamp-on and uses these to derive the resistance measurement.
Click to expand...

Sorry incorrect , it supplies a known current into a unknown loop.
 
dereckbc said:
Sorry incorrect , it supplies a known current into a unknown loop.
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That would require a constant-current source, which means the voltage would have to vary to keep the current constant. The trester induces an unknown current via a known voltage, and measures the resultant current, which is used to calculate the resistance.

A clamp-on resistance meter has two separate cores in the clamp, one of which is basically a PT, which induces a known voltage (via the turns ratio, thus the constant voltage), and the other of which is a CT, just as in any clamp-on ammeter.

From AEMC's site, read page 16:

http://www.aemc.com/techinfo/techworkbooks/ground_resistance_testers/950-WKBK-GROUND-WEB.pdf
 
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