A useful addition to your toolkit

C

Cursitor Doom

Guest
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.
 
On Sun, 05 Mar 2017 07:44:18 -0800, John Larkin wrote:

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.
Click to expand...

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. ;-)

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.
Click to expand...

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.
 
On Sun, 5 Mar 2017 14:48:51 -0000 (UTC), Cursitor Doom
<curd@notformail.com> wrote:

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.
Click to expand...

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
 
On Sun, 5 Mar 2017 16:18:50 -0000 (UTC), Cursitor Doom
<curd@notformail.com> wrote:

On Sun, 05 Mar 2017 07:44:18 -0800, John Larkin wrote:

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.

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. ;-)

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.

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.
Click to expand...

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
 
On 05/03/2017 15:44, John Larkin wrote:
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.
Click to expand...

Tell that to a condition monitoring engineer!
 
John Larkin wrote:

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.
Click to expand...

** Mains current waveforms are VERY interesting, but not if all you can see is 60Hz. A Hall effect transducer is needed to do the job properly.

The one is use is by LEM and has response to 100kHz, allows me to see currents as low as 1mA and up to 100A peak.


..... Phil
 
In article <fuhobcdhvlfcm9ik7kk4kr9fkddfpa1jon@4ax.com>,
jjlarkin@highlandtechnology.com says...
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.
Click to expand...

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.
 
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
http://www.foxsmercantile.com
 
On Sun, 5 Mar 2017 15:07:41 -0600, Foxs Mercantile <jdangus@att.net>
wrote:

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
Click to expand...

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


--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On 3/5/2017 3:37 PM, John Larkin wrote:
> Looks expensive, and I'd guess not very accurate.

<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
http://www.foxsmercantile.com
 
Foxs Mercantile wrote...
John Larkin wrote:
Looks expensive, and I'd guess not very accurate.

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
Click to expand...

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
 
On Sun, 05 Mar 2017 07:44:18 -0800, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

On Sun, 5 Mar 2017 14:48:51 -0000 (UTC), Cursitor Doom
curd@notformail.com> wrote:

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.

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.
Click to expand...

I generally use a ferrite (pi filter) on the supplies to uCs and DSPs
for EMI, then substitute a shunt to measure the power during test.
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.
Click to expand...

The old HP current probe was a great debugging tool.
 
On 3/6/2017 1:56 AM, Foxs Mercantile wrote:
On 3/5/2017 11:58 PM, rickman wrote:

Seems to me it would be a *great* tool for finding where the
currents are going. I thought that would be a good thing?

It is. But some people have difficulty accepting anything more
complicated than a light bulb, or more expensive than a pack of
cigarettes.
Click to expand...

You mean like thermal cameras?

--

Rick C
 
On 3/5/2017 4:37 PM, John Larkin wrote:
On Sun, 5 Mar 2017 15:07:41 -0600, Foxs Mercantile <jdangus@att.net
wrote:

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

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

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
 
On Sun, 05 Mar 2017 19:56:44 +0000, JM <dontreplytothis173@gmail.com>
wrote:

On 05/03/2017 15:44, John Larkin wrote:
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.

Tell that to a condition monitoring engineer!
Click to expand...

I don't design AC power supplies any more. I can buy an entire nice
PFC switcher for less than I could buy a 60 Hz power transformer.
Since the supplies all come with UL/CE/VDE/etc stickers, I don't care
about their input current waveforms.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On 3/5/2017 11:58 PM, rickman wrote:
Seems to me it would be a *great* tool for finding where the
currents are going. I thought that would be a good thing?
Click to expand...

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
http://www.foxsmercantile.com
 
On Mon, 06 Mar 2017 00:56:56 -0600, Foxs Mercantile wrote:

It is. But some people have difficulty accepting anything more
complicated than a light bulb, or more expensive than a pack of
cigarettes.
Click to expand...

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!
 
On Mon, 6 Mar 2017 00:56:56 -0600, Foxs Mercantile <jdangus@att.net>
wrote:

On 3/5/2017 11:58 PM, rickman wrote:

Seems to me it would be a *great* tool for finding where the
currents are going. I thought that would be a good thing?

It is. But some people have difficulty accepting anything more
complicated than a light bulb, or more expensive than a pack of
cigarettes.
Click to expand...

It's not hard to figure where current is going: just measure voltage
drops. What's sometimes difficult is quantifying it.

Just now we're laying out a 10-layer board with two ground planes and
three power planes. There are 22 power supplies. Most of the power
distribution will be interestingly-shaped interleaved pours, not
traces, on various layers.

That magnetic gadget would be hopelessly confused. Multiple currents
and various return paths would make it useless.

My favorite tool for tracing unusual current flows is my Flir E45
thermal imager. It cost $12,000.

We just demoed a cool new thermal imager, mounted on a nice little
stand, with its own display and also USB interfaced for pics or
movies. They're going to let us keep it.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
Cursitor Doom wrote:
On Mon, 06 Mar 2017 00:56:56 -0600, Foxs Mercantile wrote:

It is. But some people have difficulty accepting anything more
complicated than a light bulb, or more expensive than a pack of
cigarettes.

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

http://www.ebay.com/itm/201842524936

Claims to be able to handle up to 100A!
Click to expand...

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.

They don't get even.

They go for over unity! ;-)
 
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