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Anonymous Poster

Principle of DC clamp meter

06/07/2008 7:03 AM

What is the principle of a DC clamp meter ? I understand the principle of a AC clamp meter as there is a change of flux but if you have a stabilised DC current, how can a current be inducted into the clamp ???
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Electroman
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#1

Re: Principle of DC clamp meter

06/07/2008 8:42 AM

A current cannot be injected into the clamp only a magnetic flux can be sustained.

A simple hall effect device can be used to sense the dc magnetism in the clamp and used to indicate the strength of the magnetic field and hence the current causing it.

The better dc clamps use a hall effect device but also have a coil on the clamp so that when a magnetic field is sensed a current is injected into the secondary coil to offset the magnetic field and return the hall effect device's out put back to zero - the current injected is then proportional to the measured current in the primary.

John.

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double_j_b
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#2
In reply to #1

Re: Principle of DC clamp meter

06/09/2008 10:15 AM

Excellent answer but it provokes a question.

Is this why you have to zero your clamp on ammeter when using it for D/C voltages?

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Electroman
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#3
In reply to #2

Re: Principle of DC clamp meter

06/09/2008 10:18 AM

I've never designed or even used one, so I didn't know you had to zero the meter!!

However, that would be the case when using a hall effect device!

John

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double_j_b
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#4
In reply to #3

Re: Principle of DC clamp meter

06/09/2008 10:41 AM

Ah!

Thanks for the reply though I think you would be correct in the case of the hall effect.

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Anonymous Poster
#6
In reply to #1

Re: Principle of DC clamp meter

07/31/2009 1:54 AM

Good, Can you I expect more clear explanation on this? Then what is meant by Hall Effect?

Kesavamoorthy
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Emjay4119
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#7
In reply to #6

Re: Principle of DC clamp meter

07/31/2009 2:05 AM

Hall effect is the voltage that appears across the edges of a current carrying conductor in a magnetic field. Modern detectors use a piece of the semiconductor used in the chip as the sensing conductor. Check out the Alegro site for some excellent explanations including various devices and their applications. For me to explain it fully here would once again be an essay, the published information is very good so I won't try and better it. If you have something specific that doesn't gel then by all measn come back.
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Emjay4119
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#5

Re: Principle of DC clamp meter

06/10/2008 6:21 AM

I could explain the device with an essay or direct you to the excellent material available on the LEM (of Switzerland and US) site. LEM manufacture "Closed loop Hall Effect measuring systems", which is what your DC tong tester is these days.
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Anonymous Poster
#8

Re: Principle of DC clamp meter

01/20/2010 3:17 PM

Can v use clamp meter on the VFD out put to get the current accurately in case of frequency less then the power frequency?
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