Driver to drive?

[John Larkin]

On Mon, 6 Mar 2017 18:26:39 -0800 (PST), dagmargoodboat@yahoo.com
wrote:

On Monday, March 6, 2017 at 9:08:58 AM UTC-5, piglet wrote:
On 06/03/2017 13:47, George Herold wrote:
On Monday, March 6, 2017 at 5:28:11 AM UTC-5, piglet wrote:
If it's a kelvin connection to the pcb trace then you could neatly
disregard the trace resistance by injecting a servo current to bring the
IR drop to zero.

Huh, push current back through the voltage leads of the Kelvin connection.
I drew that but now I've got all the current flowing through the voltage
leads... seems like I need yet another pair of leads.. A six wire "Kelvin"
connection. Or I didn't draw it right.

George H.


piglet


So imagine a pcb trace carrying the unknown load current. Place four
test probes in a line along that trace. Measure the voltage between the
inner pair and inject a current through the outer pair such that the
voltage measured is reduced to zero. The current you have to inject will
be the same magnitude but opposite direction to the unknown load current.

piglet

You don't need to cancel the trace current--just injecting a calibrated
a.c. current between the two probes would be good enough to measure the
trace resistance, then compute the d.c. current from the d.c. drop.

Cheers,
James Arthur

Just power the board down and measure the trace resistance!

Another trick is to measure the drop in a trace, add a dummy load
resistor, note the delta-v, and do the math.

Or measure the trace resistance on a bare board from the same batch.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[John Larkin]

On Mon, 6 Mar 2017 21:17:32 -0800 (PST), dagmargoodboat@yahoo.com
wrote:

On Tuesday, March 7, 2017 at 12:00:32 AM UTC-5, John Larkin wrote:
On Mon, 6 Mar 2017 18:26:39 -0800 (PST), dagmargoodboat@yahoo.com
wrote:

On Monday, March 6, 2017 at 9:08:58 AM UTC-5, piglet wrote:
On 06/03/2017 13:47, George Herold wrote:
On Monday, March 6, 2017 at 5:28:11 AM UTC-5, piglet wrote:
If it's a kelvin connection to the pcb trace then you could neatly
disregard the trace resistance by injecting a servo current to bring the
IR drop to zero.

Huh, push current back through the voltage leads of the Kelvin connection.
I drew that but now I've got all the current flowing through the voltage
leads... seems like I need yet another pair of leads.. A six wire "Kelvin"
connection. Or I didn't draw it right.

George H.


piglet


So imagine a pcb trace carrying the unknown load current. Place four
test probes in a line along that trace. Measure the voltage between the
inner pair and inject a current through the outer pair such that the
voltage measured is reduced to zero. The current you have to inject will
be the same magnitude but opposite direction to the unknown load current.

piglet

You don't need to cancel the trace current--just injecting a calibrated
a.c. current between the two probes would be good enough to measure the
trace resistance, then compute the d.c. current from the d.c. drop.


Just power the board down and measure the trace resistance!

Sure, but we're talking an automated instrument do that all in one go,
without having to make a separate 4-wire resistance measurement.

Another trick is to measure the drop in a trace, add a dummy load
resistor, note the delta-v, and do the math.

Or measure the trace resistance on a bare board from the same batch.

I like the magnetic probe for qualitative info. Maybe a Hall probe
could do it too.

We need a FLIR for magnetic flux.

It would be cool to see the mag fields around a board.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[George Herold]

On Monday, March 6, 2017 at 9:26:46 PM UTC-5, dagmarg...@yahoo.com wrote:

On Monday, March 6, 2017 at 9:08:58 AM UTC-5, piglet wrote:
On 06/03/2017 13:47, George Herold wrote:
On Monday, March 6, 2017 at 5:28:11 AM UTC-5, piglet wrote:
If it's a kelvin connection to the pcb trace then you could neatly
disregard the trace resistance by injecting a servo current to bring the
IR drop to zero.

Huh, push current back through the voltage leads of the Kelvin connection.
I drew that but now I've got all the current flowing through the voltage
leads... seems like I need yet another pair of leads.. A six wire "Kelvin"
connection. Or I didn't draw it right.

George H.


piglet


So imagine a pcb trace carrying the unknown load current. Place four
test probes in a line along that trace. Measure the voltage between the
inner pair and inject a current through the outer pair such that the
voltage measured is reduced to zero. The current you have to inject will
be the same magnitude but opposite direction to the unknown load current.

piglet

You don't need to cancel the trace current--just injecting a calibrated
a.c. current between the two probes would be good enough to measure the
trace resistance, then compute the d.c. current from the d.c. drop.

OK next you'll be synchronously detecting the AC. :^)
George H.

Cheers,
James Arthur

 

On Tuesday, March 7, 2017 at 8:43:01 AM UTC-5, George Herold wrote:

On Monday, March 6, 2017 at 9:26:46 PM UTC-5, dagmarg...@yahoo.com wrote:
On Monday, March 6, 2017 at 9:08:58 AM UTC-5, piglet wrote:
On 06/03/2017 13:47, George Herold wrote:
On Monday, March 6, 2017 at 5:28:11 AM UTC-5, piglet wrote:
If it's a kelvin connection to the pcb trace then you could neatly
disregard the trace resistance by injecting a servo current to bring the
IR drop to zero.

Huh, push current back through the voltage leads of the Kelvin connection.
I drew that but now I've got all the current flowing through the voltage
leads... seems like I need yet another pair of leads.. A six wire "Kelvin"
connection. Or I didn't draw it right.

George H.


piglet


So imagine a pcb trace carrying the unknown load current. Place four
test probes in a line along that trace. Measure the voltage between the
inner pair and inject a current through the outer pair such that the
voltage measured is reduced to zero. The current you have to inject will
be the same magnitude but opposite direction to the unknown load current.

piglet

You don't need to cancel the trace current--just injecting a calibrated
a.c. current between the two probes would be good enough to measure the
trace resistance, then compute the d.c. current from the d.c. drop.

OK next you'll be synchronously detecting the AC. :^)
George H.

Of course, that's the reason for using a.c.!

Cheers,
James Arthur

 

On Tuesday, March 7, 2017 at 1:17:36 AM UTC-4, dagmarg...@yahoo.com wrote:

Another trick is to measure the drop in a trace, add a dummy load
resistor, note the delta-v, and do the math.

Or measure the trace resistance on a bare board from the same batch.

I like the magnetic probe for qualitative info. Maybe a Hall probe
could do it too.

We need a FLIR for magnetic flux.

Cheers,
James Arthur

Hello James,

That would called an EMSCAN.
https://www.emscan.com/

- Wolfgang.

 

On Tuesday, March 7, 2017 at 10:35:15 AM UTC-5, wolfgangf...@gmail.com wrote:

On Tuesday, March 7, 2017 at 1:17:36 AM UTC-4, dagmarg...@yahoo.com wrote:

Another trick is to measure the drop in a trace, add a dummy load
resistor, note the delta-v, and do the math.

Or measure the trace resistance on a bare board from the same batch.

I like the magnetic probe for qualitative info. Maybe a Hall probe
could do it too.

We need a FLIR for magnetic flux.

Cheers,
James Arthur

Hello James,

That would called an EMSCAN.
https://www.emscan.com/

- Wolfgang.

AWESOME.

Cheers,
James Arthur

 

[Cursitor Doom]

On Mon, 06 Mar 2017 21:36:47 -0800, John Larkin wrote:

> It would be cool to see the mag fields around a board.

That's easy. Just sprinkle it with iron fillings. ;->

 

[whit3rd]

On Tuesday, March 7, 2017 at 10:14:18 AM UTC-8, Cursitor Doom wrote:

On Mon, 06 Mar 2017 21:36:47 -0800, John Larkin wrote:

It would be cool to see the mag fields around a board.

That's easy. Just sprinkle it with iron fillings. ;-

Or the modern equivalent

<http://www.arborsci.com/magnetic-field-viewer-film-9in-x-7-2in>

 

[Cursitor Doom]

On Tue, 07 Mar 2017 14:03:19 -0800, whit3rd wrote:

Or the modern equivalent

http://www.arborsci.com/magnetic-field-viewer-film-9in-x-7-2in

That promo shot looks terrible.

 

On Tue, 7 Mar 2017 07:35:06 -0800 (PST), wolfgangfriedrich42@gmail.com
wrote:

On Tuesday, March 7, 2017 at 1:17:36 AM UTC-4, dagmarg...@yahoo.com wrote:

Another trick is to measure the drop in a trace, add a dummy load
resistor, note the delta-v, and do the math.

Or measure the trace resistance on a bare board from the same batch.

I like the magnetic probe for qualitative info. Maybe a Hall probe
could do it too.

We need a FLIR for magnetic flux.

Cheers,
James Arthur

Hello James,

That would called an EMSCAN.
https://www.emscan.com/

We have one of those. Great tool when we can't get chamber time. ;-)

 

On Wednesday, March 8, 2017 at 11:21:58 AM UTC-4, Winfield Hill wrote:

Phil Hobbs wrote...

krw wrote:
wolfgangfriedrich wrote:
dagmarg wrote:

We need a FLIR for magnetic flux.

Cheers,
James Arthur

Hello James,

That would called an EMSCAN.
https://www.emscan.com/

We have one of those. Great tool when we can't get chamber time. ;-)

What did it set you back?

Yes, looks really expensive.


--
Thanks,
- Win

Not sure, I would guess somewhere in the lower 5 figures range.
That's what it was ~10 years back when the support box was the size of a desktop PC and you would need a specific spectrum analyser with GPIB interface along side. My old office was a short drive from their location, so we never bought one but used them as consultants.
Once the device showed us a standing wave of a higher harmonic of a clock on a FFC. A really great debugging tool.
Cheers,
- Wolfgang.

 

[Phil Hobbs]

On 03/07/2017 08:56 PM, krw@notreal.com wrote:

On Tue, 7 Mar 2017 07:35:06 -0800 (PST), wolfgangfriedrich42@gmail.com
wrote:

On Tuesday, March 7, 2017 at 1:17:36 AM UTC-4, dagmarg...@yahoo.com wrote:

Another trick is to measure the drop in a trace, add a dummy load
resistor, note the delta-v, and do the math.

Or measure the trace resistance on a bare board from the same batch.

I like the magnetic probe for qualitative info. Maybe a Hall probe
could do it too.

We need a FLIR for magnetic flux.

Cheers,
James Arthur

Hello James,

That would called an EMSCAN.
https://www.emscan.com/

We have one of those. Great tool when we can't get chamber time. ;-)

What did it set you back?

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[Winfield Hill]

Phil Hobbs wrote...

krw@notreal.com wrote:
wolfgangfriedrich42@gmail.com wrote:
dagmarg...@yahoo.com wrote:

We need a FLIR for magnetic flux.

Cheers,
James Arthur

Hello James,

That would called an EMSCAN.
https://www.emscan.com/

We have one of those. Great tool when we can't get chamber time. ;-)

What did it set you back?

Yes, looks really expensive.


--
Thanks,
- Win

 

On Wed, 8 Mar 2017 09:36:21 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 03/07/2017 08:56 PM, krw@notreal.com wrote:
On Tue, 7 Mar 2017 07:35:06 -0800 (PST), wolfgangfriedrich42@gmail.com
wrote:

On Tuesday, March 7, 2017 at 1:17:36 AM UTC-4, dagmarg...@yahoo.com wrote:

Another trick is to measure the drop in a trace, add a dummy load
resistor, note the delta-v, and do the math.

Or measure the trace resistance on a bare board from the same batch.

I like the magnetic probe for qualitative info. Maybe a Hall probe
could do it too.

We need a FLIR for magnetic flux.

Cheers,
James Arthur

Hello James,

That would called an EMSCAN.
https://www.emscan.com/

We have one of those. Great tool when we can't get chamber time. ;-)


What did it set you back?

Dunno. I think it was bought before I was hired (5 years).

 

On Wed, 8 Mar 2017 09:00:18 -0800 (PST), wolfgangfriedrich42@gmail.com
wrote:

On Wednesday, March 8, 2017 at 11:21:58 AM UTC-4, Winfield Hill wrote:
Phil Hobbs wrote...

krw wrote:
wolfgangfriedrich wrote:
dagmarg wrote:

We need a FLIR for magnetic flux.

Cheers,
James Arthur

Hello James,

That would called an EMSCAN.
https://www.emscan.com/

We have one of those. Great tool when we can't get chamber time. ;-)

What did it set you back?

Yes, looks really expensive.


--
Thanks,
- Win

Not sure, I would guess somewhere in the lower 5 figures range.
That's what it was ~10 years back when the support box was the size of a desktop PC and you would need a specific spectrum analyser with GPIB interface along side. My old office was a short drive from their location, so we never bought one but used them as consultants.
Once the device showed us a standing wave of a higher harmonic of a clock on a FFC. A really great debugging tool.
Cheers,
- Wolfgang.

I think that's about right ($20K-$30K). A mere bag of shells compared
to a lot of other EMI tools (ever price out a 3M chamber? ;-). Well
worth the money.

 

[whit3rd]

On Wednesday, March 8, 2017 at 7:21:58 AM UTC-8, Winfield Hill wrote:

Phil Hobbs wrote...

krw@notreal.com wrote:
wolfgangfriedrich42@gmail.com wrote:
dagmarg...@yahoo.com wrote:

We need a FLIR for magnetic flux.

That would called an EMSCAN.
https://www.emscan.com/

We have one of those. Great tool when we can't get chamber time. ;-)

What did it set you back?

Yes, looks really expensive.

Can you still get disclosing fluid? It was a paramagnetic liquid, usually
in a spraybottle, that indicates field. Used on mag tape (or floppies)
it tells you whether your eight-track tape recorder is firing on all eight tracks.

Kyread is the brand I've used. It evaporates and leaves no residue.

I think it's a fluid-in -fluid suspension, and droplets elongate in response to
field strength and direction.

 

[Bill Martin]

On 03/07/2017 02:03 PM, whit3rd wrote:

On Tuesday, March 7, 2017 at 10:14:18 AM UTC-8, Cursitor Doom wrote:
On Mon, 06 Mar 2017 21:36:47 -0800, John Larkin wrote:

It would be cool to see the mag fields around a board.

That's easy. Just sprinkle it with iron fillings. ;-

Or the modern equivalent

http://www.arborsci.com/magnetic-field-viewer-film-9in-x-7-2in

Huh? "Bulk magnetic field viewing film, 9in. x 7.2in. Can be cut up into
student sizes for the whole class to explore magnetic fields. Or use it
in a complete sheet to see an entire magnet's field lines."

Those must be small students...

 

On Saturday, March 11, 2017 at 4:22:20 PM UTC-5, Tom Del Rosso wrote:

John Larkin wrote:

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.

I once asked if a discarded head from an old, old hard disk could do
that.

Excellent idea. HD heads should be fast, too.

Cheers,
James Arthur

 

I once asked if a discarded head from an old, old hard disk could do
that.

>Excellent idea.  HD heads should be fast, too.

You'd need to read from the write head, though. Read heads have been magnetoresistive for over a decade, and they take more TLC.


Cheers

Phil Hobbs

(Who was taking magnetic force microscope pictures of MR heads in 1989ish.)

 

On Saturday, March 11, 2017 at 8:58:12 PM UTC-5, pcdh...@gmail.com wrote:

I once asked if a discarded head from an old, old hard disk could do
that.


Excellent idea.  HD heads should be fast, too.

You'd need to read from the write head, though. Read heads have been magnetoresistive for over a decade, and they take more TLC.


Cheers

Phil Hobbs

(Who was taking magnetic force microscope pictures of MR heads in 1989ish..)

What's wrong with using magnetoresistance for current-sensing?

In fact, that prompts an entirely naive thought: MRAM as magnetic
imaging array (with suitable modification).

Cheers,
James Arthur