Batteryless current clamps?
Fester Bestertester
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.
Proteus IIV
CURIOUSITY KILLED THE CAT
GO TO SCHOOL AND HEAR IT FROM THE HORSES NOUTH
OR GO TO YOUR NEAREST TECHINAL BOOK STORE AND PURCHASE TEST METERS
FOR DUMMIES
I AM PROTEUS
Bill Sloman
Try to find out where the caps lock is, and unlock it. At the moment
you like more like Prostheticus.
For future reference, if you don't know the answer to a question, it
is not helpful to tell people that it is in some unspecified technical
book somewhere.
If you can identify a specific book that has a specific reference to
the problem - with the ISBN for the book and the page or chapter
reference for the helpful bit - you can earn brownie points without
providing a direct answer.
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.
--
Bill Sloman, Nijmegen
Jeroen Belleman
> [...]
> Try to find out where the caps lock is, and unlock it. At the moment
> you like more like Prostheticus.
>
> For future reference, if you don't know the answer to a question, it
> is not helpful to tell people that it is in some unspecified technical
> book somewhere.
You could have added a line for the OP, saying that a passive
current clamp is a transformer, or some such.
Jeroen Belleman
Tim Williams
> I'm curious how the Fluke i200s current clamp probe can give mV output
> without the use of batteries.
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
John Fields
<bill....@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.
JF
pimpom
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.
John Larkin
Hey, it's been too long. The only time we hear from you is when your
kid sister kicks you off the Xbox.
John
Joel Koltner
news:0001HW.C7279C6F...@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
John Fields
<zapwireD...@yahoo.com> wrote:
>"Fester Bestertester" <f...@fbt.net> wrote in message
>news:0001HW.C7279C6F...@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:7ar5g59hdrcdpu3ic...@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
Joel Koltner
news:sir5g5h9h69vfurap...@4ax.com...
> news:7ar5g59hdrcdpu3ic...@4ax.com
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
> Nope, it'll get you nothing. :-)
> Know why?
Because the federales will toss your rear in jail quite rapidly?
---Joel
pimpom
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.
John Fields
---
Nope, because the magnetic field generated by the power line will never
cut the conductor wrapped around it since the conductor will be
essentially perpendicular to the varying field. :-)
JF
Bill Sloman
> On Tue, 17 Nov 2009 05:39:40 -0800 (PST),Bill Sloman
>
> >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
Martin Riddle
"Joel Koltner" <zapwireD...@yahoo.com> wrote in message
news:U6BMm.34563$Vr1....@en-nntp-01.dc1.easynews.com...
You need a loop to form an air core transformer, which this has been
done.
Cheers
Bill Sloman
> Bill Slomanwrote:
Unfortunately, I don't know that. There are several ways in which a
current clamp can work, and not all of them depend on on the clamp
acting as a transformer.
--
Bill Sloman, Nijmegen
Proteus IIV
>
> - Show quoted text -
THIS IS NO GAME
YOUR HEADS UP MAY HELP THE GROUP THOUGH
I HAVE ALREADY GIVEN MY INPUT TO THIS TOPIC
I AM PROTEUS
John Fields
<bill....@ieee.org> wrote:
>On Nov 17, 3:10�pm, Jeroen Belleman <jer...@nospam.please> wrote:
>> Bill Slomanwrote:
>> > [...]
>> > Try to find out where the caps lock is, and unlock it. At the moment
>> > you like more like Prostheticus.
>>
>> > For future reference, if you don't know the answer to a question, it
>> > is not helpful to tell people that it is in some unspecified technical
>> > book somewhere.
>> > [...]
>>
>> You could have added a line for the OP, saying that a passive
>> current clamp is a transformer, or some such.
>
>Unfortunately, I don't know that.
---
Finally owning up to your ignorance, huh?
---
>There are several ways in which a
>current clamp can work, and not all of them depend on on the clamp
>acting as a transformer.
---
Really?
How about some examples, then, Mr. Bullshit Artist, and don't forget
that the keyword here is "passive".
JF
John Fields
<bill....@ieee.org> wrote:
>On Nov 17, 4:29�pm, John Fields <jfie...@austininstruments.com> wrote:
>> On Tue, 17 Nov 2009 05:39:40 -0800 (PST),Bill Sloman
>>
>> <bill.slo...@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.
---
As usual, more of your evasion since, clearly, the reference was to your
waste of bandwidth caused by the unhelpful abuse you heap on JT while
condemning PROTEUS for the waste of bandwidth caused by his unhelpful
abuse of Fester Bestertester.
True hypocrisy.
---
>People who use text-books know about this stuff. Try and remember back
>to when you did.
---
An insult in an attempt to change the subject and put me on the
defensive, huh?
It won't work, you contemptible, fatuous ass.
JF
John Fields
wrote:
---
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.
A transformer is used to transfer _power_ from a source into a load,
thus the power, P2, required by the load, will be that power, P1,
supplied by the source.
In an ideal transformer there will be no losses, and then P1 and P2 will
be equal.
Next, the voltages on the primary and the secondary will be directly
proportional to the ratio of the number of turns on the primary to the
number of turns on the secondary, and the currents in them will
inversely proportional to the turns ratio.
With that in mind, let's say we have a transformer with a one turn
primary and a 1000 turn secondary, across which is connected a 1000 ohm
resistor which is dropping one volt.
The current in the load will then be:
E 1.0V
I = --- = ------ = 1e-3 ampere = 1 milliampere
R 1e3R
and the power dissipated by the load:
P = IE = 1e-3A * 1V = 1e-3 watt = 1 milliwatt
Now, since the turns ratio is 1000:1, the current in the primary is
inversely proportional to the current in the secondary, and since the
current in the secondary is 1 milliamp, the current in the primary must
be:
Is * nS 1e-3A * 1000t
IP = --------- = -------------- = 1 ampere
nP 1t
If we now double the current in the primary, the current in the
secondary will be doubled as well, causing the 1000 ohm resistor to drop
2 volts.
If we triple the primary current, the secondary current will be tripled
as well, the resistor will drop 3 volts, and so on...
So, what we have is a device which will have an output voltage which is
directly proportional to the input current and which we can use to
determine the input current by measuring the output voltage.
JF
Bill Sloman
> On Tue, 17 Nov 2009 15:01:11 -0800 (PST),Bill Sloman
>
>
>
> <bill.slo...@ieee.org> wrote:
> >On Nov 17, 4:29 pm, John Fields <jfie...@austininstruments.com> wrote:
> >> On Tue, 17 Nov 2009 05:39:40 -0800 (PST),Bill Sloman
>
> >> <bill.slo...@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.
>
> ---
> As usual, more of your evasion since, clearly, the reference was to your
> waste of bandwidth caused by the unhelpful abuse you heap on JT while
> condemning PROTEUS for the waste of bandwidth caused by his unhelpful
> abuse of Fester Bestertester.
>
> True hypocrisy.
Jim Thompson is notoriously enthusiastic about plonking people he
disagrees with. Someone who took him seriously might be upset by it.
This strikes me as information that Proteus IIV might find useful.
If I felt like heaping abuse on Jim Thompson I'd be more explicit
about it.
> >People who use text-books know about this stuff. Try and remember back
> >to when you did.
>
> ---
> An insult in an attempt to change the subject and put me on the
> defensive, huh?
>
> It won't work, you contemptible, fatuous ass.
The image of the incorrigibly offensive John Fields ever being put on
the defensive is amusing. Not as amusing as the idea that you might
ever have consulted a text-book, but distinctly comical all the same.
But we can rely on you for seriously side-splitting - if unintentional
- comedy. The clown who still thinks that the 555 is the answer to
every circuit problem imagines that he can call somebody else a
fatuous ass.
--
Bill Sloman, Nijmegen
Bill Sloman
> On Tue, 17 Nov 2009 10:59:38 -0800, "Joel Koltner"
>
> >"John Fields" <jfie...@austininstruments.com> wrote in message
> >news:sir5g5h9h69vfurap...@4ax.com...
> >>news:7ar5g59hdrcdpu3ic...@4ax.com
>
> >5uA... nice!
>
> >Seems that someone on eBay is selling a +/-5uA movement:
>
> >> Nope, it'll get you nothing. :-)
> >> Know why?
>
> >Because the federales will toss your rear in jail quite rapidly?
>
> ---
> Nope, because the magnetic field generated by the power line will never
> cut the conductor wrapped around it since the conductor will be
> essentially perpendicular to the varying field. :-)
Since the original claim was
" >Wrapping some turns around the power company's lines will get you
many, many
>watts. :-)"
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
Bill Sloman
If one can rely on that "passive". Someone who knew a little more than
you might extract some of the power circulating through the wire and
produce an active solution without an external power source.
--
Bill Sloman, Nijmegen
Fester Bestertester
> 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.
After watching the 3 Stooges act that is aee / sed...
Sheesh!
I AM FBt
Pointless Posts
Admitted that the S/N ratio on Usenet can be frustrating. But did
you stop to consider the possibility that a) you failed to grasp
other attempts to explain it to you; b) your question was so
elementary for *this* group that few people bothered; c) your
last post might be taken as a slap in the face by those who tried
to help.
John Fields
<bill....@ieee.org> wrote:
>On Nov 17, 9:28�pm, John Fields <jfie...@austininstruments.com> wrote:
>> On Tue, 17 Nov 2009 10:59:38 -0800, "Joel Koltner"
>>
>> <zapwireDASHgro...@yahoo.com> wrote:
>> >"John Fields" <jfie...@austininstruments.com> wrote in message
>> >news:sir5g5h9h69vfurap...@4ax.com...
>> >>news:7ar5g59hdrcdpu3ic...@4ax.com
>>
>> >5uA... nice!
>>
>> >Seems that someone on eBay is selling a +/-5uA movement:
>> >http://cgi.ebay.com/Weston-Bakelite-Glass-5ua-microamp-Panel-Meter-Hi...
>>
>> >> Nope, it'll get you nothing. :-)
>> >> Know why?
>>
>> >Because the federales will toss your rear in jail quite rapidly?
>>
>> ---
>> Nope, because the magnetic field generated by the power line will never
>> cut the conductor wrapped around it since the conductor will be
>> essentially perpendicular to the varying field. :-)
>
>Since the original claim was
>
>" >Wrapping some turns around the power company's lines will get you
>many, many
>>watts. :-)"
>
>This isn't the reason - lines is plural and the nett current through
>the lines as a bunch balances out to zero.
---
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
power company's lines, which I addressed by referring to it as "the
power line".
---
>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.
---
Yeah, but so what???
What he was talking about was wrapping some turns around the conductor,
like this:
. OOOOOOOOOOOOO
.----------------------
.
.----------------------
. OOOOOOOOOOOOO
Where the dashed lines represent one of the power conductors and the
'O's represent the "some turns" wrapped around it.
Do you think current will be induced in the solenoid if it's wound that
way?
JF
John Fields
---
Bullshit, liar.
What you were doing was telling P3 to clean up his act or you'd plonk
him, and then, out of the blue, you just _had_ to take another little
snipe at Jim.
I guess you just can't get over his reporting you to the FBI, huh?
---
>If I felt like heaping abuse on Jim Thompson I'd be more explicit
>about it.
>
>> >People who use text-books know about this stuff. Try and remember back
>> >to when you did.
>>
>> ---
>> An insult in an attempt to change the subject and put me on the
>> defensive, huh?
>>
>> It won't work, you contemptible, fatuous ass.
>
>The image of the incorrigibly offensive John Fields ever being put on
>the defensive is amusing. Not as amusing as the idea that you might
>ever have consulted a text-book, but distinctly comical all the same.
---
Geez, Bill, I get along pretty well with most everyone here and post
mostly on topic, while you seem to be perpetually offensive to
_everyone_ and on topic about 1% of the time, so I think a _big_ PKB is
in order at this point.
---
>But we can rely on you for seriously side-splitting - if unintentional
>- comedy. The clown who still thinks that the 555 is the answer to
>every circuit problem imagines that he can call somebody else a
>fatuous ass.
---
Geez, Bill, even if it were true that I thought the 555 was the be-all
end-all circuit design element you say I think it is, that doesn't make
you any less of a fatuous ass, does it?
JF
John Fields
<bill....@ieee.org> wrote:
>On Nov 18, 2:46�pm, John Fields <jfie...@austininstruments.com> wrote:
>> On Wed, 18 Nov 2009 00:35:12 -0800 (PST),Bill Sloman
>> <bill.slo...@ieee.org> wrote:
>> >There are several ways in which a
>> >current clamp can work, and not all of them depend on on the clamp
>> >acting as a transformer.
>>
>> ---
>> Really?
>>
>> How about some examples, then, Mr. Bullshit Artist, and don't forget
>> that the keyword here is "passive".
>
>If one can rely on that "passive".
---
Can't come up with anything, huh? What a surprise!!!
---
>Someone who knew a little more than
>you might extract some of the power circulating through the wire and
>produce an active solution without an external power source.
---
I guess that'll keep you out of the running, n'est-ce pas?
JF
Fester Bestertester
> you stop to consider the possibility that a) you failed to grasp
> other attempts to explain it to you; b) your question was so
> elementary for *this* group that few people bothered; c) your
> last post might be taken as a slap in the face by those who tried
> to help.
Right you are.
A big thank you to those responders who gave answers to my question. Much
appreciated.
My comment was addressed to the "noise". :-)
FBt
Bill Sloman
> On Wed, 18 Nov 2009 08:36:17 -0800 (PST),Bill Sloman
I don't plonk anybody, and I certainly wasn't threatening that I'd
plonk him
> I guess you just can't get over his reporting you to the FBI, huh?
If he'd known how much pleasure I was going to get out of pointing how
how seriously far out of touch with reality that proved him to be, he
probably wouldn't have done it. I know he is conscious of his duty to
protect his country, but it isn't as if he is fanatical about it.
Even you will have to admit it has to be the funniest prat-fall we've
ever had around here.
> >If I felt like heaping abuse on Jim Thompson I'd be more explicit
> >about it.
>
> >> >People who use text-books know about this stuff. Try and remember back
> >> >to when you did.
>
> >> ---
> >> An insult in an attempt to change the subject and put me on the
> >> defensive, huh?
>
> >> It won't work, you contemptible, fatuous ass.
>
> >The image of the incorrigibly offensive John Fields ever being put on
> >the defensive is amusing. Not as amusing as the idea that you might
> >ever have consulted a text-book, but distinctly comical all the same.
>
> ---
> Geez, Bill, I get along pretty well with most everyone here and post
> mostly on topic, while you seem to be perpetually offensive to
> _everyone_ and on topic about 1% of the time, so I think a _big_ PKB is
> in order at this point.
> ---
Nice to see you sending yourself up from time to time. There have been
times when I've imagined that you lack a sense of humour, but that
really is funny. Nice one.
> >But we can rely on you for seriously side-splitting - if unintentional
> >- comedy. The clown who still thinks that the 555 is the answer to
> >every circuit problem imagines that he can call somebody else a
> >fatuous ass.
>
> ---
> Geez, Bill, even if it were true that I thought the 555 was the be-all
> end-all circuit design element you say I think it is, that doesn't make
> you any less of a fatuous ass, does it?
Or any more. Your judgement isn't all that great outside of
electronics either.
--
Bill Sloman, Nijmegen
Bill Sloman
Nice try.
<snipped the rest>
--
Bill Sloman, Nijmegen
Bill Sloman
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
John Nagle
> On Nov 18, 6:08 pm, Fester Bestertester <f...@fbt.net> wrote:
>>> On Tue, 17 Nov 2009 00:18:55 -0800, Fester Bestertester <f...@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
DaveC
> 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
Tzortzakakis Dimitrios
? "Fester Bestertester" <f...@fbt.net> ?????? ??? ??????
news:0001HW.C7279C6F...@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.
>
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
John Fields
---
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
alternating current carrying conductor can be used to extract power from
the varying magnetic field surrounding that conductor.
Nothing could be further from the truth, as demonstrated here:
news:26iag5hjpub42ookl...@4ax.com
Since, conveniently, you don't have access to abse, I'll take the
liberty of emailing you the photos as soon as I post this.
Enjoy. :-)
JF
Fester Bestertester
tapped single winding) with a range switch to select the winding?
John Larkin
wrote:
>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?
Current transformers are usually dumped into a load resistor aka
burden resistor, to convert their output current into voltage. I'm
sure the Fluke clamp-on has an internal burden resistor, and they may
switch that to change ranges.
Without a burden resistor, the output voltage will be proportional to
frequency and very dependent on core reluctance, which would be fatal
for a clamp-on meter with a hinge and a non-repeatable air gap.
Coreless Rogowsky coils are used unloaded, but need a downstream
integrator to accurately measure current.
http://en.wikipedia.org/wiki/Rogowski_coil
The coolest current transformer is a second-harmonic DCCT, accurate to
parts-per-million from DC to many kilohertz.
http://www.gmw.com/electric_current/Danfysik/866_867/867.html
John
George Herold
Wiki's great thanks John. That second link didn't have much info on
how the device works. Is the following the same thing?
http://adweb.desy.de/mdi/CARE/Lyon/Lyon%20DCCT_Technology_Review.pdf
(I googled second-harmonic DCCT)
George H.
Bill Sloman
> On Wed, 18 Nov 2009 15:08:46 -0800 (PST),Bill Sloman
Your enthusiasm for inventing implausible straw men knows no bounds. I
never made any such claim. My scepticism about you claim was purely
based on the fact that you were ignoring what Joel Koltner had
actually said.
> Nothing could be further from the truth, as demonstrated here:
>
> news:26iag5hjpub42ookl...@4ax.com
>
> Since, conveniently, you don't have access to abse, I'll take the
> liberty of emailing you the photos as soon as I post this.
>
> Enjoy. :-)
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
John Larkin
Fig 3 is about right. The green feedback path is usually an N-turn
winding to net an N-to-1 current transformer.
There are usually two physical toroids. Ib, If, and T3 are wound on
both, as if they were a single core. T1 and T2 are each wound on one
of the cores, in opposite directions so that there's no net coupling
of the carrier frequency into T3 or the customer's Ib circuit.
The AC path (sense winding T3 and its amplifier, driving If) fight to
keep the flux zero at higher frequencies. The second-harmonic system
works at low frequencies, again to keep net core flux zero, which
happens when Ib = N * If.
I designed one of these once. It was fun, and not all that easy.
John
daestrom
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
John Fields
---
What Joel _actually_ said was that energy could be extracted from the
varying magnetic field surrounding a power line by wrapping turns around
it.
Since you pointed out that energy can't be had by wrapping turns around
bundled conductors carrying charge flowing in opposite directions,
that's something that, obviously, every dunce realizes.
Knowing that, my take on Koltner's lighthearted comment was that he was
referring to a single conductor, such as the ones used in high voltage
distribution systems which are called, by the way, "power lines".
---
>> Nothing could be further from the truth, as demonstrated here:
>>
>> news:26iag5hjpub42ookl...@4ax.com
>>
>> Since, conveniently, you don't have access to abse, I'll take the
>> liberty of emailing you the photos as soon as I post this.
>>
>> Enjoy. :-)
>
>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.
---
You're really not much of an objective, honest, truth-seeking scientist,
are you?
If you're as smart as you unabashedly keep on proclaiming you are, you
should know very well what the pictures show; that energy cannot be
extracted from the varying magnetic field surrounding a conductor with a
solenoid-wound coil, but can be readily extracted using a
toroidally-wound coil.
Of course you have to feign ignorance and invoke indifference because
your position, from a technical point of view is untenable and you know
it, so in order to save face, instead of simply admitting error, you
resort to subterfuge.
---
>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.
---
Geez, Dr. Sloman, even for you that's pretty stupid.
Have you never even considered that getting "free" power involves
tapping into the lines on the energy company's side of the meter?
---
>Joel Koltner made a rather good joke, which you have totally failed to
>get.
---
Trying to make trouble, huh?
I have no quarrel with Joel and I don't think he has one with me since
all I did was apprise him, with no rancor, (with a little humor, even)
of the reason why one can't use a solenoid oriented coaxially with a
conductor carrying AC to extract energy from the varying field.
You, on the other hand, do nothing _but_ try to foment discord when your
errors are exposed, in an effort to diffuse the focus and allow you to
exit, without brickbats, from the melee you created in the first place.
JF
John Fields
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.
---
Indeed.
Thank you. :-)
JF
Tzortzakakis Dimitrios
? "John Larkin" <jjla...@highNOTlandTHIStechnologyPART.com> ?????? ???
?????? news:dnsag51jfmub8nppj...@4ax.com...
shorted. In the generating facilities in Kozani, West Macedonia, where 400
kV current transformers were involved, the operators of the plant had a
special indicator whether the secondary was shorted.
daestrom
Some old switchboard CT's I worked on in the Navy had very thin
insulator between two spring clips. Whenever we wanted to remove a
meter for cal, we slip the insulator out so the two clips would short
together, shorting the CT. Then we could open circuit the meter and
remove it from the panel. I don't remember exactly what the blade was
made of, but it's surface wasn't perfectly smooth like polished
material, more porous like unglazed ceramic (of course it wasn't any metal).
The reason they built the insulator so thin was that if one accidentally
open-circuited the CT without removing the wafer first, the high voltage
developed by the CT would just 'punch thru' the wafer and safely short
the CT. Then all you had to do to repair things was make sure you
closed the circuit and replace the wafer-thin insulator blade.
Was kind of surprised when I moved to commercial power systems that they
didn't use something similar. Just has to have a breakdown voltage that
is low enough to avoid damaging the CT.
daestrom
John Larkin
wrote:
Lower-power CT, like residential-metering size, 100 amps or so, will
generally tolerate being unloaded. They will saturate and make two
not-too-huge voltage spikes per cycle and not get very warm. The nasty
part is that, once the burden is reconnected, they are very likely to
wind up magnetized, which will mess up low-current accuracy.
John
JosephKK
<tmor...@gmail.com> wrote:
>On Nov 17, 2:18 am, Fester Bestertester <f...@fbt.net> wrote:
>> I'm curious how the Fluke i200s current clamp probe can give mV output
>> without the use of batteries.
>
>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.
Actually about equally ferrite and plastic with copper coming at about
1/3 either of those. No battery whatsoever and AC only.
>
>They also read DC, and have an offset knob to account for the
>ferrite's hysteresis.
Only active probes do that.
>
>The passive probes only read AC, and as I recall, are 1 or 10 mV/A.
>
>Tim
I can make any output ratio i want, i know how they work.
Bill Sloman
> On Thu, 19 Nov 2009 10:43:58 -0800 (PST),Bill Sloman
Wrapping turns around a high voltage power line probably wouldn't be a
good idea.
<snip>
--
Bill Sloman, Nijmegen
John Fields
---
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
the line by a coaxial solenoid surrounding the line?
JF
JosephKK
There is no CT in residential metering, the energy meter is connected
directly. Even commercial / light industrial you do not see CTs in
the meter circuit until 600 A, and before that you are typically at
480 V 3-phase (in the US).
John Larkin
Of course there is. I delivered over 1800 electronic submetering units
for the Battery Park City apartment complex, and, trust me, we used
CTs. Lots of electronic meters use CTs. You should get out more.
John
James Sweet
>
> There is no CT in residential metering, the energy meter is connected
> directly. Even commercial / light industrial you do not see CTs in
> the meter circuit until 600 A, and before that you are typically at
> 480 V 3-phase (in the US).
My uncle's house (in the US) has a 400A service with current
transformers. They're not common but they do exist. IIRC 200A is the
largest residential meter.
John Larkin
It's dangerous to make catagorical statements like "There is no CT in
residential metering." It only takes one counter-case to make you
wrong.
John
Michael A. Terrell
Like the claim that no US homes have three phase power that was made
on this group (alt.engineering.electrical) a few years ago.
--
The movie 'Deliverance' isn't a documentary!
John Fields
---
He said, with his last breath, and then quietly sank into the sea...
JF