clamp on multimeter

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Hi guys,

I'm looking for a good clamp on multimeter than does AC and DC, current and
voltages, and most importantly I want to do ALL using the clamp.

A lot of clamp meters I see will only do amps with the clamp and you have to
pull out the test leads for voltage. Are there any you would reccomend that
I can do everything with just the clamp ? (other than ohms/continuity, etc)

Looking for something reasonably priced too (~$100 - $150), not some $300+


Re: clamp on multimeter

It is easy to design a clamp on meter to measure AC amps, much more difficult
and expensive to measure DC amps. I don't think it is possible to measure
voltage with a clamp on meter.

Skeleton Man wrote:
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                   Mike Walsh

Re: clamp on multimeter

Mike Walsh wrote:  *** and top-posted.  Fixed.  ***
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This (voltmeter via clamp) is fundamentally impossible.  Just think
for a few moments about the way information is transmitted to a
clamp.  Clamps are handy for current measurement, especially AC.
For voltage you basically need probes.

Please do not top-post.  Your answer belongs after (or intermixed
with) the quoted material to which you reply, after snipping all
irrelevant material.  See the following links:

  < (taming google)
  < (newusers)

In addition, your lines should be limited to 72 (better 67) chars.

 [mail]: Chuck F (cbfalconer at maineline dot net)
 [page]: <
            Try the download section.

Re: clamp on multimeter

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This is NOT your forum
and you do not get to make the rules here.


Re: clamp on multimeter

On Tue, 16 Sep 2008 17:41:52 -0500, "philo"

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He's not an idiot IMO, just stubbornly refusing to see why
there needs to be a standardized format on usenet, and
perhaps failing to recognize that what he writes is for
others to read, not for his own reading so there really
isn't any good reason to not write with the formatting
others have chosen.

Re: clamp on multimeter

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The reason I called him that was as you stated...
where the "form" of the advice becomes more important than the advice
itself. Though Usenet of course has conventions,
there are no such rules.

Reminds me of:

The Purist
by Ogden Nash

A conscientious scientist,
Trustees exclaimed, "He never bungles!"
And sent him off to distant jungles.
Camped on a tropic riverside,
One day he missed his loving bride.
She had, the guide informed him later,
Been eaten by an alligator.
Professor Twist could not but smile.
"You mean," he said, "a crocodile."

Re: clamp on multimeter

I can see how a fluctuating magnetic field can be use to determine rate
of change of flux to figure out the A/C amps through a line by using a
clamp-around ammeter.  Since the magnetic flux is constant with D/C
current and since field strength changes per the square of the distance
and since you won't be able to properly position the clamp, measuring
D/C amps would be problematic and probably require much more expensive
equipment than some hand-held device.  Voltage is the pressure or
electromotive force in the circuit and I don't see how you'll ever
measure that with an field-effect ammeter.  A 100V circuit and a 50kV
circuit might produce the same 1 ampere flow which would have the same
field strength despite the EMF to push that ampere through the circuit.
It's been 35 years since I've been in college physics classes so I
might've forgotten something.  I just don't see how you can measure EMF
based on field strength which is determined by amperage, not voltage.
Also, voltage is a differential measurement across 2 points and not
always from ground so how would a single clamp be able to measure the
DIFFERENCE in voltaic potential?

Even at $300+, have YOU found any clamp-around meters that measure
voltage?  Or D/C current?

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Re: clamp on multimeter

VanguardLH wrote:
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I have a clamp-on meter. It measures both DC and AC current, via
the magnetic field. It is likely to use this as the internal

The clamp-on meter is mainly intended for current. It may have
plug holes for voltage measurements, but then the form factor
of the unit doesn't lend itself to stuffing a lot of
extra functions in there. I prefer a clamp-on meter for
current, and a regular multimeter for volts-ohms-hfe-capacitance-frequency.

This is my clamp on meter. Extech 380947. The jaws on mine are grey
in color, and the unit is a number of years old. It didn't
have any fancy NIST calibration.

DC amps                40A/400A
AC amps (True RMS)     4A/40A/100A/400A

I've used the DC 400A scale, while working on the starter
motor of my car. The meter has peak detection and detected the starter
motor drawing 150 amps peak in cold weather starting.

For PC usage, I use the DC 40A scale, which is good for things
like the 16A DC that one of my older PCs is using on the
5V rail.

I haven't had need of high AC current ranges, and the
compressor on central air conditioning, is probably the
highest AC current device I've measured (maybe 10amps
or so at 220VAC).

You cannot measure AC current by clamping the unit around an
ordinary AC line cord. The magnetic fields around the two
current carrying conductors, cancel. I have a "cheater cord"
for 115V circuits, where the insulation is removed from a
section of the extension cord, and the three wires inside
are exposed. By clamping around one of the current carrying
wires, the current can be measured. The "cheater cord" is
also available from some vendors, as an optional accessory,
which is why I made my own for nothing (just a ruined
extension cord).

The unit adds current flows. For example, if I have four
wires, carrying DC 4A, 3A, 3.5A, 3.2A, and then I place
all four wires within the jaws, the instrument correctly
reports 13.7A total. The magnetic field generated around
the wire is additive.

I worked with Hall Probes for a short time, back in school.
They have a tendency for zero drift, so for the most
accurate measurements, you want to zero the offset
before making the measurement. Since there is probably
a bit of heat generated in the probe, it may take
a few seconds to stabilize. But other than that, it
is a nice technology, as you don't have to cut
any conductors to measure current. Especially nice
when working on the 220VAC powered central air


Re: clamp on multimeter

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I understand the Hall probes for detecting magnetic fields and strength
bias but I wasn't sure about a *cheap* clamp probe (your model isn't
just pocket change) would accurately measure a non-fluctuating field
(i.e., D/C current).  The specs you gave on your model say that it has
1% accuracy for D/C current (same for A/C current).  I was thinking
that positioning would be important for D/C current measurement but then
upon thinking about it I realized that the induced current on one side
would be stronger while the other side would be weaker so it would
average out and be unsensitive to your placement of the clamp around the

Good to know.  Thanks.

Re: clamp on multimeter

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That's correct.
For voltage you need to use the leads
as voltage exists *across* a junction.

Re: clamp on multimeter

Skeleton Man wrote:

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I don't see any clamp-on voltage meters even from Fluke; their clamp-
ons require the test leads for voltage measurements.

Everyday Practical Electronics or Nuts & Volts magazine had a
construction project about making an AC/DC clamp-on probe with a
linear Hall effect chip.  Basically, you buried a Hall sensor in a
magnetic core.

MCM Electronics sells an AC/DC clamp-on probe for digital meters.
Mine cost $32, delivered, but I think the price has gone up since

Don't overlook Sears for stuff like this because they had an AC/DC
clamp-on with voltage meter (not true RMS) for $80.  Join their
Craftsman club because they sometimes send out discount coupons or
offer special prices.

Re: clamp on multimeter

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<quote>  I want to do ALL using the clamp </quote>   Electronically
impossible, sorry.

Current can be calculated by measuring the magnetic field surrounding a
conductor, AC more easily so, DC with extra electronics.
A typical low cost example is the QM1563 from Jaycar

Voltage on the other hand to be measured accurately must employ probes to
contact the points with the voltage potential.
The QM1563 mentioned above includes a Digital voltmeter for such
measurements, it also includes other measurement facilities like Resistance,
Frequency and Capacitance.

There 'are' devices on the market that will indicate the 'presence' of a
voltage by beeping and/or flashing a light.
The QP2279 from is a typical example of this type of tool.
Note they will only indicate the presence of 'a' voltage, relying in the
main on the detection of the magnetic field surrounding a conductor.
They will not give you any idea of the voltage carried by the wires.
To measure the voltage of the wires involved you will have to use the probes
of a Voltmeter.


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