Re: PCB in-circuit test: how do ATE machines measure resistors?

zigbee@xxxxxxxxx wrote:

On 3 Apr, 13:21, Friedrich Seuhs <friedrich.se...@xxxxxxxxx> wrote:
zig...@xxxxxxxxx wrote:
Hi folks,

does anybody know how ATE machine measures the value of a resistor
placed on the target PCB?

I know that ATE machines, through a bed of nail, inject a certain
voltage onto the test point.

Also, what happens if the resistor under measure is connected to other
resistors?

thanks for any help,
Enrico

Many years ago I programmed a incircuit tester. There was a solution like
this:
You have 3 resistors in a delta connection. The 3 nodes are numered 1, 2,
3 with its resistors R12, R13, R23. Connect a voltage between 1 an 2,
connect the same voltage between 1 and 3. --> U23 = 0 -->
I(R23) = 0.
I(R12) = U/R12
I(R13) = U/R13

The current nail 1 = I(R12) + I(R13)
The current nail 2 = I(R12) + I(R23) = I(R12)
The current nail 3 = I(R13) + I(R23) = I(R13)

Hope this helps.
--
Freundliche Grüsse -- Regards
F. Seuhs
Mailto: friedrich.se...@xxxxxxxxx

Hi, thanks for your answer.

First of all, I just discovered that PCB in-circuit test are carried
out keeping the board UNPOWERED.

I also found on this Google book, a couple of schematics:

"Building a successful board-test strategy" by Stephen F. Scheiber

They usually use 3 signals:

1. A voltage source (constant or sinusoidal)
2. An inverting Op.Amp. that shows Virtual Earth
3. Optionally a "Guard" GND that helps isolate the Part under test

That's exactly what I ment in my posting.


As far as you know, is it possibile to distinguish 2 capacitance in
parallel?

I would say: NO !!


Enrico

--
Freundliche Grüsse -- Regards
F. Seuhs
Mailto: friedrich.seuhs@xxxxxxxxx
.

Relevant Pages