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Topic: ORCON Ammeter question

Sam Hunter
Jedi Master Film Handler

Posts: 779
From: West Monroe, LA, USA
Registered: Jan 2002

posted 08-29-2003 12:57 PM

If you run dc through a transformer you get nothing on the other side.

The dc amp meter has to work on a different principal than an ac meter.

Maybe I am wrong about AC meters but I dont think so.

I left the above to reflect a change in knowledge [Big Grin]

I found this info on the net and now I understand:

"The actual movement mechanism of a clamp-on ammeter is much the same as for an iron-vane instrument, except that there is no internal wire coil to generate the magnetic field. More modern designs of clamp-on ammeters utilize a small magnetic field detector device called a Hall-effect sensor to accurately determine field strength. Some clamp-on meters contain electronic amplifier circuitry to generate a small voltage proportional to the current in the wire between the jaws, that small voltage connected to a voltmeter for convenient readout by a technician. Thus, a clamp-on unit can be an accessory device to a voltmeter, for current measurement. "

Enquiring mind(s) wanted to know.

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Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 08-29-2003 01:43 PM

Tim, is there a chance the DC clamp measures the electro-static field? If you stuff a magnet in it, it won't see it. I don't know... [Confused]

I remember an old DC line clamp that had to be calibrated everytime it was used. Calibration was done by holding the clamp next to the wire, and then the meter was adjusted for zero. Then the clamp was placed around the wire to obtain a reading. It was an old unit going back to the 1970's and it's acccuracy was not that great as compared to middle-of-the-road DC line clamps.

I have one that will do AC and DC with a digital read-out. I think it costed about 200 bucks, but it is accurate.

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Sam Hunter
Jedi Master Film Handler

Posts: 779
From: West Monroe, LA, USA
Registered: Jan 2002

posted 08-29-2003 01:48 PM

Makes you say hmmmmmm doesn't it?
I emailed a meter manufacturer about it and am awaiting his reply.

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 08-29-2003 02:39 PM

DC and AC clamps use a Hall effect transitor that measures the magnetic field around the cable Some in the DC mode measure the disturbance in a field of the clamp

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Sam Hunter
Jedi Master Film Handler

Posts: 779
From: West Monroe, LA, USA
Registered: Jan 2002

posted 08-29-2003 02:44 PM

Yep, thats what I found out. (see above)

I got an answer from the manufacturer.

quote:
Greetings,

Thank you for your e-mail of 29 August 03.

The smaller ones generally use a Hall effect sensor in a gap in the core. This senses the magnetic field set up by the current in the aperture of the core.

Ours are different. Like US Patent 3768011, we build a core with winding resembling a current transformer. This is connected across a special peak current limited inverter. When direct current flowing through the aperture of the core upsets the magnetic state of the core, the inverter changes duty factor so as to send an average (DC) current back to the winding to nearly restore the balance of the core. We measure this restorative current and use it to provide an output and drive a meter.

Ours is a distributed sensor, also suited for building larger clamps.

I hope this helps.

[ 08-29-2003, 03:45 PM: Message edited by: Sam Hunter ]

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Tim Reed
Better Projection Pays

Posts: 5246
From: Northampton, PA
Registered: Sep 1999

posted 08-29-2003 03:46 PM

Sam, you answered your own question! [Smile]

quote:
Tim, is there a chance the DC clamp measures the electro-static field?

I'm not sure on the internal specifics of the meter (other than what Sam uncovered), but it's obviously using the field around the conductor in some manner.

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