A useful addition to your toolkit

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https://www.sparkfun.com/products/11005

Replace the existing connector with a BNC, add a bit of series resistance  
and you have a *very* cheap current probe for your scope.

Re: A useful addition to your toolkit
On Sun, 5 Mar 2017 14:48:51 -0000 (UTC), Cursitor Doom

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I have a clamp-on ammeter that pretty much does that, although it just
indicates amps, and doesn't allow waveform snooping. 60 Hz waveforms
aren't terribly interesting.

My real problem with current measurement is DC, on PC boards. We want
to know how much current, say, an FPGA is using. Sometimes I include
current shunts in a layout, but sometimes I don't.

One can use existing switcher inductors as current shunts. I wish I
had a PCB trace current probe, but that's probably not posssible. You
can measure millivolt and microvolt drops across traces and vias.




--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: A useful addition to your toolkit
On Sun, 05 Mar 2017 07:44:18 -0800, John Larkin wrote:

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Indeed they're not. But your meter is presumably *only* designed for use  
at 60Hz, I would imagine. Hook it up to a 100Hz signal and you'll see  
nothing at all in all probability. ;-)

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Do they even exist? That would be amazing but no doubt *way* beyond what  
I can justify to splash out on as a mere hobbyist.


Re: A useful addition to your toolkit
On Sun, 5 Mar 2017 16:18:50 -0000 (UTC), Cursitor Doom

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A 1" long, 20 mil wide 1oz trace will be about 25 milliohms. 1 amp
makes 25 millivolts, and lots of cheapish DVMs will resolve that well
enough. You probably need a bench DVM with microvolt resolution to
measure, say, 1 amp running through a via, but you could build a
little microvolt meter or amp pretty easily. PCB trace and via
resistances need to be calibrated, which is only a minor nuisance.

Here are some pcb-trace shunts, down near the connector:

https://dl.dropboxusercontent.com/u/53724080/PCBs/TEM2_Power_Board.JPG

One of the great mysteries of electronics is "where is the current
going?" Sometimes a thermal imager helps figure that out. A little
magnetometer would be fun, not hard to do these days.




--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: A useful addition to your toolkit
snipped-for-privacy@highlandtechnology.com says...
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Reading the blurb on the cited current transformer reminded me of a  
puzzle for all clamp meters... Surely they are no good clamped on a  
normal bi-directional power cable in which the current is both coming  
and going: the magnetic fields will near-perfectly cancel out. Surely  
you have to split the cable to measure current?

Mike.

Re: A useful addition to your toolkit
They do make special current probes specifically for doing traces
on a PC board. without cutting traces or requiring a loop of wire.
<http://www.power-mag.com/pdf/feature_pdf/1327592496_TTI_Layout_1.pdf


--  
Jeff-1.0
wa6fwi
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Re: A useful addition to your toolkit
wrote:

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Looks expensive, and I'd guess not very accurate.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: A useful addition to your toolkit
On 3/5/2017 3:37 PM, John Larkin wrote:
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<http://www.aimtti.us/product-category/current-probes/aim-i-prober-520
It is expensive. At $795 for the basic probe.
Data sheet:
<http://resources.aimtti.com/datasheets/prec-iprober520-5p.pdf
Instruction manual:
<http://resources.aimtti.com/manuals/I-prober_Instruction_Manual-Iss5.pdf



--  
Jeff-1.0
wa6fwi
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Re: A useful addition to your toolkit
Foxs Mercantile wrote...
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 The expense we can handle, if, for example, it'll
 give us adequate help in debugging our switching
 power supply designs.  But the calibrating scheme
 for trace current measurements looks iffy.  But
 maybe along with other measurements, power in,
 voltage and power out, etc., it could do the job.
 It is fast enough to look at inductor currents.


--  
 Thanks,
    - Win

Re: A useful addition to your toolkit
On 3/5/2017 4:37 PM, John Larkin wrote:
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Seems to me it would be a *great* tool for finding where the currents  
are going.  I thought that would be a good thing?

--  

Rick C

Re: A useful addition to your toolkit
On 3/5/2017 11:58 PM, rickman wrote:
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It is. But some people have difficulty accepting anything more
complicated than a light bulb, or more expensive than a pack of
cigarettes.


--  
Jeff-1.0
wa6fwi
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Re: A useful addition to your toolkit
On 3/6/2017 1:56 AM, Foxs Mercantile wrote:
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You mean like thermal cameras?

--  

Rick C

Re: A useful addition to your toolkit
On Mon, 06 Mar 2017 00:56:56 -0600, Foxs Mercantile wrote:

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For the *real* cheapskates out there, there's this alternative:

http://www.ebay.com/itm/100A-SCT-013-000-Non-invasive-AC-current-sensor-
Split-Core-Transformer-YH-/201842524936?
hash=item2efec08308:g:vm8AAOSwCGVX3BYF

Claims to be able to handle up to 100A!


Re: A useful addition to your toolkit
Cursitor Doom wrote:
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    Let's see you use it to find a stray 100 mA DC on a crowded circuit  
board.  :(


--  
Never piss off an Engineer!

They don't get mad.

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Re: A useful addition to your toolkit
On Mon, 06 Mar 2017 20:56:02 -0500, Michael A. Terrell wrote:

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Oh come along now. You know it's not intended for that sort of usage!

Re: A useful addition to your toolkit
Cursitor Doom wrote...
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 I ordered one from Newark, and plan to use it
 on my messed-up switching power-supply designs.
 Qualitative results will be fine.


--  
 Thanks,
    - Win

Re: A useful addition to your toolkit
On Wed, 08 Mar 2017 05:44:39 -0800, Winfield Hill wrote:

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Mine arrived today. I plan to monitor fuel injection impulses with it  
firstly just to see what kind of di/dt responses it's capable of. I'm not  
quite as confident as you are, though!

Re: A useful addition to your toolkit
Cursitor Doom wrote...
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 I do a lot of fast HV pulsing circuitry, and don't
 expect it'll be helpful for that kind of work.  But
 the 5MHz bandwidth should be fine for looking at
 inductor current ramps, cap charge-discharge, etc.


--  
 Thanks,
    - Win

Re: A useful addition to your toolkit
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a few years back there was talk of using a video head from a VCR
(after removing it from the drum) to probe AC currents. It should be good
to a few megahertz. a core from an ethernet transformer with a gap
added could be another option. a spool-shaped inductor would
probably work too.


--  
This email has not been checked by half-arsed antivirus software  

Re: A useful addition to your toolkit

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A little unshielded drum-core inductor is a handy h-field probe.


--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

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