Batteryless current clamps?

I'm curious how the Fluke i200s current clamp probe can give mV output without the use of batteries.
How is this done? If one is measuring 200A I can see how the magnetic field
could generate enough current in the probe to support some high-impedance, low-draw circuitry.
But when measuring on the low scale, say, 2 or 3 amps, how could the probe output a few hundred mV? (The clamp is spec'd to output 100mV / amp on the 20A low scale, 10mV on the 200A high scale.)
Can someone explain this to me? I'm fascinated to see it's possible & curious to know how.
Thanks.
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Is that the one with the 10/100 switch and a green LED?
I'm pretty sure most of the weight is not ferrite, it's a battery somewhere.
They also read DC, and have an offset knob to account for the ferrite's hysteresis.
The passive probes only read AC, and as I recall, are 1 or 10 mV/A.
Tim
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On Tue, 17 Nov 2009 07:20:32 -0800 (PST), Tim Williams

Actually about equally ferrite and plastic with copper coming at about 1/3 either of those. No battery whatsoever and AC only.

Only active probes do that.

I can make any output ratio i want, i know how they work.
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Fester Bestertester wrote:

You seem to have a preconceived notion of what constitutes large, small and insignificant currents levels in terms of the fields they generate, but such categorisations are only relative. "2 or 3 amps" is quite huge in some contexts and generate an appreciable flux in the magnetic core of the clamp. The alternating magnetic field induces a voltage in the clamp's pickup coil and this voltage can certainly reach "a few hundred mV" if enough number of turns are used.
You can also think of the clamp as a current transformer. The wire being measured for current is the primary and the pickup coil of the DMM is the secondary.
If you're more familiar with voltage transformers, think of it this way: Suppose you have just 1 mV output from a microphone. Connect it to the primary of a 1:10 transformer and you will get 10 mV at the secondary terminals. Use a 1:100 transformer and you get 100 mV and so on, theoretically up to any voltage.
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At some level, if you wrap a transformer around a wire, you can extract as much or as little power as you like. Consider that, say, 100mV (generated by a 1A flow in the one turn "primary" of your current probe) fed into the 10k impedance of a multimeter is all of 1 *micro*watt, which is pretty much "nothing" in comparison to what the primary is likely to be carrying (e.g., even 1A at 1V is a watt, a million times higher).
The power is coming from the primary, of course: The load on the secondary is reflected back to the primary -- multiplied by the turns ratios of the transformer squared and all. (This load effectively appear in series with thatever the real load on the primary is.) The trick then, is finding sensitive enough meters that the burden on the primary is minimized. You might be surprised at how sensitive some of the old analog meters (galvanometers) are -- 1mA full-scale deflection is what you find in the cheapest instruments, 100uA is found in many mid-grade instruments, and 10uA (and even less) is found in high-end gear.

Wrapping some turns around the power company's lines will get you many, many watts. :-)
---Joel
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On Tue, 17 Nov 2009 09:32:34 -0800, "Joel Koltner"

--
news: snipped-for-privacy@4ax.com
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5uA... nice!
Seems that someone on eBay is selling a +/-5uA movement: http://cgi.ebay.com/Weston-Bakelite-Glass-5ua-microamp-Panel-Meter-High-Z_W0QQitemZ130344240372

Because the federales will toss your rear in jail quite rapidly?
---Joel
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Joel Koltner wrote:

http://cgi.ebay.com/Weston-Bakelite-Glass-5ua-microamp-Panel-Meter-High-Z_W0QQitemZ130344240372
I don't think that's quite what John meant. Anyway, that reminds me of a practice by some villagers in my area. They cannot afford, or don't want to pay, the power connection charge and monthly bills. They wire their homes for a few incandescent bulbs and keep a pair of solid-cored wires with the ends stripped bare and bent into a U shape, the other two ends feeding the house wiring. When it gets dark, they use a dry bamboo pole to hook the bare ends to the overhead power lines. Free power - until they get caught. The power company - the government here - usually does nothing more than reprimand the offenders, but the practice is rare now.
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On Tue, 17 Nov 2009 10:59:38 -0800, "Joel Koltner"

--
Nope, because the magnetic field generated by the power line will never
cut the conductor wrapped around it since the conductor will be
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Since the original claim was
" >Wrapping some turns around the power company's lines will get you many, many

This isn't the reason - lines is plural and the nett current through the lines as a bunch balances out to zero.
Wrapping a clamp-on meter around one line means that there is current circulating around the clamp - the current that goes through the selected line in one direction is matched by equal and opposite current flowi g through the other lines in the other direction. The coupling coefficient is unlikely to be good, but it is finite.
-- Bill Sloman, Nijmegen
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On Wed, 18 Nov 2009 08:46:00 -0800 (PST), Bill Sloman

--
Since that's obvious to the most casual observer, the context of his
statement must have been about wrapping some turns around [one] of the
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Nice try.
<snipped the rest>
-- Bill Sloman, Nijmegen
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On Wed, 18 Nov 2009 15:08:46 -0800 (PST), Bill Sloman

--
Of course, you fraud, since by snipping the rest you sidestep the issue,
which is your ignorance in believing that a solenoid wound around an
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The pictures were perfectly clear. It was less obvious what you were actually doing, but since I couldn't care less, this isn't any great loss.
The joke is that even if you do extract "many watts" from the power company's power lines, you won't be stealing from them. In order to be able to extract power you have to be drawing power for which you will be billed, and any extra watts you extract by transformer action is subtracted from the power you are already paying for - your paid for load will be seeing a lower drive voltage.
Joel Koltner made a rather good joke, which you have totally failed to get.
-- Bill Sloman, Nijmegen
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Bill Sloman wrote:

If you make a 'tap' upstream of the revenue meter, even with just transformer action, you're stealing. Revenue meters (kilowatt-hour meters) have always had terminal voltage as one of their inputs. An illegal tap upstream may affect the voltage at the service entrance some small amount, but the metering will reduce the billed kWh accordingly. So regardless of the exact voltage supplied by the utility (it often varies slightly throughout the day), the amount of energy delivered at the service entrance is what is billed for. Power drawn off before the meter isn't measured and is 'stolen'.
Of course if you just 'wrap some turns around the power line' without orienting the coil properly in relation to the line, you're not going to get any power because transformer action won't work when your turns of wire are parallel to the power line's magnetic field (i.e. 'wrapped around' the power line). And I think that was John Field's point.
daestrom
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wrote:

--
Indeed.

Thank you. :-)
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On Thu, 19 Nov 2009 10:43:58 -0800 (PST), Bill Sloman

--
What Joel _actually_ said was that energy could be extracted from the
varying magnetic field surrounding a power line by wrapping turns around
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Wrapping turns around a high voltage power line probably wouldn't be a good idea.
<snip>
-- Bill Sloman, Nijmegen
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On Fri, 20 Nov 2009 10:43:14 -0800 (PST), Bill Sloman

--
So, then, you agree that, aside from the obvious danger of wrapping
turns around a high voltage line, no appreciable power can be drawn from
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On Fri, 20 Nov 2009 10:43:14 -0800 (PST), Bill Sloman

--
He said, with his last breath, and then quietly sank into the sea...

JF

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