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Old 16th October 2003, 02:54 AM   #1
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Default How to use clamp meters

Hiyee,
As above...I have never dealt with high voltages and high currents that need a clamp meter to measure...but just for the sake of information...can anyone tell me how a typical clamp meter is used?? I haven't got one yet...so maybe just a bit of info would be useful...hehehe...can't stop an inquisitive mind eh??
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Old 16th October 2003, 07:08 AM   #2
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Default Clamp meter for current measurement

AC clamp meters the cheap and common ones....
The clamp meters that I've come across have jaws that close around the conductor (wire) that carriess the current in question.
The wire then becomes a 1-turn primary of a transformer, who's ring-core (toroid) is the clamp mechanism. A secondary also exists which is connected to the meter.
This kind of meter is useful for measuring high currents without disconnecting the supply. Of course they must only be clamped over a single conductor, otherwise the fields will cancel.

Another type can be used for small DC currents. These are lab instruments, and used to use an AC feed to the clamp transfomer. I guess they use some saturation effect.
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Old 16th October 2003, 08:04 AM   #3
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Quote:
Another type can be used for small DC currents. These are lab instruments, and used to use an AC feed to the clamp transfomer. I guess they use some saturation effect.
http://www.lem.ch/inet/products.nsf/...256bf1005b553a!OpenDocument

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Charles
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Old 16th October 2003, 08:07 AM   #4
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Thanks Charles
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Old 16th October 2003, 02:00 PM   #5
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Do we clamp the cable at the "jaw" or between the loop that forms around the jaws?? And there seems to be a ground cable most of the time..what do we do with it?? connect it to a suitable gnd on the circuit somewhere?? Or do I actually leave it disconnected for best results...talking about trafos...if the measured cable is placed between the jaws...does it effectively become an air-cored trafo...and does it work with DC?? Since non of the trafos I know work on DC...okok...SMPSUs do...but the have to be chopped...
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Old 16th October 2003, 02:28 PM   #6
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The jaws form the trafo core (they are made out of ferromagnetic material coated with an insulation) and therefore they have to surround the conductor whose current is to be measured.

The link I posted above is for a current sensor that is able to measure down to DC. It is therefore a little more complicated than the standard one. They actually null the field in the core by means of a hall sensor, a correction amplifier and an auxiliary coil. The nulling current through the auxiliary coil is proportional to the measured current ( & inversely proportional to the winding ratios !!).

The ordinary current converter that only allows AC measurements does not have the sensor and amp. The current in the coil is measured and inversely proportional to the winding ratios and proportional to the current in the conductor under test.

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Charles
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Old 16th October 2003, 02:33 PM   #7
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Meaning I actually clamp the cable and leave it on the "jaw" right?? or do I let it drop into the "hole" or loop formed by the closed jaw...I dun really get it here...I mean how to affix the clamp meter properly...
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Old 16th October 2003, 02:43 PM   #8
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I let it drop into the "hole" or loop formed by the closed jaw...
Exactly that !

Regards

Charles
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Old 16th October 2003, 03:02 PM   #9
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Okie thanks...I will try to get hold of a clamp meter to try it out....
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