Batteryless current clamps?
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From: Joel Koltner on 17 Nov 2009 12:32 "Fester Bestertester" <fbt(a)fbt.net> wrote in message news:0001HW.C7279C6F0007F514B08A39AF(a)news.eternal-september.org... > 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.) 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. > Can someone explain this to me? I'm fascinated to see it's possible & > curious > to know how. Wrapping some turns around the power company's lines will get you many, many watts. :-) ---Joel
From: John Fields on 17 Nov 2009 13:13 On Tue, 17 Nov 2009 09:59:39 -0600, bud-- <remove.budnews(a)isp.com> wrote: >Bill Sloman wrote: >> >> Unhelpful abuse counts as a waste of bandwidth. >> >> Raise you game or expect to be plonked. > >Please ignore the ignorant troll that infests alt.engineering.electrical. --- Sloman posts there? ;) JF
From: John Fields on 17 Nov 2009 13:48 On Tue, 17 Nov 2009 09:32:34 -0800, "Joel Koltner" <zapwireDASHgroups(a)yahoo.com> wrote: >"Fester Bestertester" <fbt(a)fbt.net> wrote in message >news:0001HW.C7279C6F0007F514B08A39AF(a)news.eternal-september.org... >> 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.) > >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. --- news:7ar5g59hdrcdpu3icb3rlmdn31iqiqfa67(a)4ax.com --- >> Can someone explain this to me? I'm fascinated to see it's possible & >> curious >> to know how. > >Wrapping some turns around the power company's lines will get you many, many >watts. :-) --- Nope, it'll get you nothing. :-) Know why? JF
From: Jim Thompson on 17 Nov 2009 15:52 On Tue, 17 Nov 2009 12:13:41 -0600, John Fields <jfields(a)austininstruments.com> wrote: >On Tue, 17 Nov 2009 09:59:39 -0600, bud-- <remove.budnews(a)isp.com> >wrote: > >>Bill Sloman wrote: >>> >>> Unhelpful abuse counts as a waste of bandwidth. >>> >>> Raise you game or expect to be plonked. >> >>Please ignore the ignorant troll that infests alt.engineering.electrical. > >--- >Sloman posts there? ;) > >JF Anywhere he can get an ego lift ;-) I'm always pleased to note that I'm the highest standard for Slowman's disdain, but please don't feed the jerk. Let him die that most unpleasant of deaths... alone ;-) -- ...Jim Thompson | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 |
From: Bill Sloman on 17 Nov 2009 18:01
On Nov 17, 4:29 pm, John Fields <jfie...(a)austininstruments.com> wrote: > On Tue, 17 Nov 2009 05:39:40 -0800 (PST),Bill Sloman > > <bill.slo...(a)ieee.org> wrote: > >Unhelpful abuse counts as a waste of bandwidth. > > >Raise you game or expect to be plonked. But don't worry if Jim > >Thompson plonks you - he plonks everybody who disagrees with him, > >which is probably one of the reasons he believes so many things that > >don't happn to be true. > > --- > Typical Slomanesque two-faced rhetoric; you damn unhelpful abuse as a > waste of bandwidth and then, in the same breath, engage in it yourself. Unhelpful abuse? I told him that if he wants to claim that the answer to a question is availlable in a textbook, he's got to tell us which text-book and whereabouts in that text-book. People who use text-books know about this stuff. Try and remember back to when you did. -- Bill Sloman, Nijmegen |