I've evidently confused this Thread with another one which had a picture of a
single point probe, approximately 0.125" in diameter,
and divided into 4-equal-quadrants each separated by about ~10-thousands of an inch.
My bad,
there are NO pictures in this thread.
The picture is still stuck in my head,
and I don't remember where it came from.

Thank-You Mr. Salts for pointing this out.

No one has mentioned a specific number regarding
the accurate Probe-Spacing of a 4-Probe arrangement,
so I was never disabused of my incorrect association of that
previous picture, which I somehow ????? associated with this Thread.

I apologize for any confusion I may have caused.

If a rigid-frame was devised that would hold the 4-Probes in a fixed pattern,
( the larger the 4-point pattern is, the more measurement-resolution there will be ),
and provisions are made for guaranteeing equal contact pressure,
and therefore equal Contact-Resistance, for each Probe-Tip,
and the surface that is supporting the Foil is completely non-Conductive,
then this idea could have some value.

The rigid-frame / holder could possibly be hinged in place, and held up with a spring
over a designated testing area to facilitate a quick "go / no-go" test.
.
.
.

 

provisions are made for guaranteeing equal contact pressure,

Don't understand your continuing concern about contact resistance.
That resistance is ignored by the constant-current source probes, and should not be a significant factor for the high impedance voltage probe measurement.
Am I missing something?

 

If a rigid-frame was devised that would hold the 4-Probes in a fixed pattern,
( the larger the 4-point pattern is, the more measurement-resolution there will be ),
and provisions are made for guaranteeing equal contact pressure,
and therefore equal Contact-Resistance, for each Probe-Tip,
and the surface that is supporting the Foil is completely non-Conductive,
then this idea could have some value.

Years ago came the requirement to test ESD mats. Because of the high resistances involved a megger was used.



The way this worked was there are two weights. The handles of the weights each had a simple string of known length joining them. Each weight weighed 5.0 Lbs. The cross sectional area of each weight was known. The weights were placed on the unit under test (ESD Mat) and the meter was read. Since the weight was known and the cross sectional area of the weights known applying 500 VDC from the megger made it easy to determine the resistance. While this crude and simple method was more than adequate for measuring if an ESD mat was go or no go what the thread starter is looking to accurately do is far more complex.

Ron

 

Don't understand you continuing concern about contact resistance.
That resistance is ignored by the constant-current source probes, and should not be a significant factor for the high impedance voltage probe measurement.
Am I missing something?

I was worried about this as well... but initial testing showed little concern. Sure, I'll use spring-loaded probe tips, but the greater concern is a rock solid current and oxide free current tips, and keeping the probes evenly aligned, with no wiggle between them.

 

How many digits (or bits) of resolution does the voltage measuring system provide? This is just about resolution, independent from accuracy and stability.

 

How many digits (or bits) of resolution does the voltage measuring system provide? This is just about resolution, independent from accuracy and stability.

3.5

 

3.5

OK, 3 1/2 digits, and that is a reasonable amount of resolution. My electrical tester used an "Analogic" brand 4 1/2 digit voltmeter along with 2 digital "settable comparators" to generate a solid accept or reject signal. Never any drift with a digital comparator., which used the parallel digital output from the meter.

My point being that the stability of the current regulator I suggest fits well within the accuracy available with that variety of meter.
IIf it were a six digit meter the potential accuracy, and the resolution, would demand a much more stable current controller.