Batteryless current clamps?
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From: Bill Sloman on 18 Nov 2009 18:25 On Nov 18, 6:08 pm, Fester Bestertester <f...(a)fbt.net> wrote: > > On Tue, 17 Nov 2009 00:18:55 -0800, Fester Bestertester <f...(a)fbt.net> > > wrote: > > >> 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. > > > --- > > OK. > > > A passive clamp-on ammeter is essentially the secondary of a transformer > > wound on a core that can be opened or closed in order to get it around a > > conductor so the current in that conductor can be measured without > > cutting it and using a conventional ammeter. > > [...] > > JF > > FINALLY an answer on-topic. Thank you. You asked about the Fluke i200s current clamp probe. I've never used one, and I'm not sure that I've even seen one, which discouraged me from trying to improvise an explanation. John Field's response - now that he has finally got around to making the kind of useful post that he claims to represent the bulk of his output - does seem to be plausible. From time to time we get responses from the people who designed the gear under discussion, but you don't seem to have been that lucky. -- Bill Sloman, Nijmegen
From: John Nagle on 18 Nov 2009 23:29 Bill Sloman wrote: > On Nov 18, 6:08 pm, Fester Bestertester <f...(a)fbt.net> wrote: >>> On Tue, 17 Nov 2009 00:18:55 -0800, Fester Bestertester <f...(a)fbt.net> >>> wrote: >>>> 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. >>> --- >>> OK. >>> A passive clamp-on ammeter is essentially the secondary of a transformer >>> wound on a core that can be opened or closed in order to get it around a >>> conductor so the current in that conductor can be measured without >>> cutting it and using a conventional ammeter. >>> [...] >>> JF >> FINALLY an answer on-topic. Thank you. Yes. Classic AC clamp-on ammeters are simply transformers. One "turn" through the clamp, many turns in the fixed coil for output. The output feeds into a voltmeter. Those are AC-only devices. There are also Hall-effect clamp-on ammeters, and those work for both AC and DC. These have been available for a decade or so, and pricing is now down as low as $60. I used to have one that could read down to about 500mA DC, and it only cost $129. Very useful in robotics and controls work. John Nagle
From: DaveC on 19 Nov 2009 01:20 [...] > There are also Hall-effect clamp-on > ammeters, and those work for both AC and DC. These have been > available for a decade or so, and pricing is now down as low as > $60. I used to have one that could read down to about 500mA DC, > and it only cost $129. Very useful in robotics and controls work. > > John Nagle Which make & model would that $129 model be? It's always useful to know someone else's favorite tools... Dave
From: Tzortzakakis Dimitrios on 19 Nov 2009 09:10 ? "Fester Bestertester" <fbt(a)fbt.net> ?????? ??? ?????? news:0001HW.C7279C6F0007F514B08A39AF(a)news.eternal-september.org... > 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. > There's nothing fancy about that, the electricity meters of a medium-voltage consumer (real and reactive energy) are powered from the two potential and the two current transformers, without any other power supply (medium voltage=15 kV in Crete). -- Tzortzakakis Dimitrios major in electrical engineering mechanized infantry reservist hordad AT otenet DOT gr
From: Fester Bestertester on 19 Nov 2009 10:29
So, for a millivolt output probe, this might be as simple as 2 windings (or a tapped single winding) with a range switch to select the winding? |