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#137786 - 07/30/03 11:46 AM Low Resistance meters?
VOLTS Offline
Member
Registered: 06/02/01
Posts: 21
Does anyone have experiance with low resistanec meters? The insurance company said we need to check our grounding connections (Chemical Plant)with a low res meter. We have been using a mulitmeter but they are dictating the meter go to micro-ohms. Any advise on brands or features I should look for?
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#137787 - 07/30/03 02:07 PM Re: Low Resistance meters?
Bjarney Offline
Moderator
Registered: 04/10/02
Posts: 2527
Loc: West-Southern Inner-Northeast ...
They may be referring to an ohmmeter that is intended to be used with Kelvin probes/leads—or 4-wire resistance measurements. {Likely the “insurance company” has no clue whatsoever of the instrument needed.}

One is AEMC model 5600.
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#137788 - 07/30/03 02:59 PM Re: Low Resistance meters?
pauluk Offline
Member
Registered: 08/11/01
Posts: 7520
Loc: Norfolk, England
VOLTS,
Did you intend this post for the non-U.S. area, or were you aiming for general for wider readership? Say the word and I'll transfer the thread if you wish.

The 4-wire ohmmeter principle goes back many, many years, but it's still a reliable method for measureing very low resistance values. You basically use two wires to pass a reasonable current through the equipment under test and use the second pair of leads to measure the voltage drop and thus calculate the resistance.

Of course, if you have a suitable source of current and voltmeter you can set-up your own ad hoc instrument in the same way.
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#137789 - 07/30/03 05:50 PM Re: Low Resistance meters?
Bill Addiss Offline
Member
Registered: 10/07/00
Posts: 3875
Loc: NY, USA
VOLTS,

Here is an Extech brand 4-wire MilliOhm Meter
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#137790 - 07/31/03 07:46 AM Re: Low Resistance meters?
Bjarney Offline
Moderator
Registered: 04/10/02
Posts: 2527
Loc: West-Southern Inner-Northeast ...
VOLTS — If your measurements need to be in the microohm range, a 10-100 ampere test current is not uncommon. If you don’t need battery portability, and can do some experimenting, something like a Sorensen 10-volt, 100-amp DC constant-current power supply will let you test connections with the millivolt scale of a multimeter—id est, 10mV/100A = 100 μΩ


[This message has been edited by Bjarney (edited 07-31-2003).]
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#137791 - 07/31/03 07:58 AM Re: Low Resistance meters?
VOLTS Offline
Member
Registered: 06/02/01
Posts: 21
No, I did not intend to post in the non-us area sorry for the mistake. Thanks to all for the information.
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