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From: Paul Carpenter on 5 Mar 2010 12:09
In article <2daa9d33-a23c-47e3-9f95-
019fb78a00de(a)z4g2000yqa.googlegroups.com>, zigbee(a)libero.it says...
> Hi guys, thanks for your valuable answers.
>
> I would like to summarize what was said so far:
>
>
> 1. I don't want to build a fully fledged ATE system
>
> 2. I need to measure the value of: resistors, capacitors, inductors
> and the diodes' polarity

Which depends on circuit configuration on how accurately you can
measure them and how long the measurements take.

You still do not show basic circuit theory for when two impedances
are in parallel (even if you are not aware of that impedance).
You do not show any understanding about time of measurements
for parallel capacitances (intentional or remainder of circuit).

> 3. We design the contact system, which is composed of:
>
> 2 covers of plexiglass milled and drilled
> 1 PCB with: 1 microcontroller + 1 DAC + 1 ADC + 1 MUX + some
> transistors + some relays + some pogo pins
> 2 caps of plexiglass milled
> 8 metal cylindric columns + some screws
>
> 4. We use the very same contact system for Functional Tests as well.
>
>
>
> I read carefully how the "SmartTweezers" measures the values of
> components and realized that's exactly what I need.
>
> Look at page 3 of: http://www.circuitcellar.com/archives/viewable/221-Bachiochi/Bachiochi-221.pdf
> The current flowing into the DUT returns to the voiltage source,
> passing through the virtual ground of an OP AMP. That's how they
> measure the current.
> I don't think it takes a genius to build a similar circuit.

But it takes some knowledge to work out how to us them and how
interpret the readings into pass/fail or correct/incorrect.

> If they sell the "SmartTweezers" as an OEM product (that is, no LCD,
> no cover, just the PCB), one can build up a portable IN-CIRCUIT TESTER
>
>
> Just to make an example, this is the Bill of Material of my last
> design (I skipped connectors and IC's):
>
> Fuse - 2 A - fast = 2
> NTC - 33 Ohm - in-rush current limiter = 1
> Capacitor 1 nF - 1 kV - ceramic = 2
> Capacitor 100 nF - 1 kV - poly = 1
> Capacitor 100 nF - 50 V - ceramic = 8
> Capacitor 100 uF - 35 V - Elec. = 1
> Capacitor 22uF - 400 V - Elec. = 1
> Common mode choke - 100 mH = 1
> Transformer for flyback converter - 4 windings - 2 mH = 1
> Diode Schottky = 2
> Diode 1N4007 = 1
> Diode BAS 16 = 1
> Transistor - BCX41 = 2
> Resistor - 220 Ohm - 2 W = 1
> Resistor - 0603 - from 220 Ohm to 10 kohm = 20
> Relay - DPDT - 2 A = 1
> Led - 0603 - red = 6

How are you going to determine a diode polarity if the diode
is a commutating or flyback diode across the relay coil?
Plenty of other configurations of diodes and transistors
where you will meet problems.

How are you going to determine the value of one resistor with
another resistor in parallel?

How long are you going to wait for a resistance measurement?

How will measure a circuit that has a bleed resistor across it?
Or for that matter the bleed resistor, not uncommon for very
large capacitors or other charge storing circuits.

To what accuracy (percentage) are you expecting to measure the
components?

What accuracy do you expect from the measurement system?

The IC's and connectors may exhibit parallel loads to your
testing (let alone shorts).

> I bet 100 $ that the SmartTweezers are able to measure'm all :-)

It will be able to take measurements, whether they will be correct
to match the component in there, or you know how to interpret the
results is another matter.

I suggest you make one and try measuring ALL the components on
several models of working products and see what readings
you get. Simpler still just use a multimeter to measure resistance
to do the resistance, diode and b-e tests, then see what answers
you get.

You show little knowledge of basic circuit theory to believe you
actually understand the simple points everyone has put to you in
the past, and are just looking for the cheapest solution and
believing it will work without understanding.

You are blinded by expecting a technology silver bullet to
just happen.

--
Paul Carpenter | paul(a)pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/> PC Services
<http://www.pcserviceselectronics.co.uk/fonts/> Timing Diagram Font
<http://www.gnuh8.org.uk/> GNU H8 - compiler & Renesas H8/H8S/H8 Tiny
<http://www.badweb.org.uk/> For those web sites you hate
From: Paul Carpenter on 5 Mar 2010 12:18
[This followup was posted to comp.arch.embedded and a copy was sent to
the cited author.]

In article <2daa9d33-a23c-47e3-9f95-
019fb78a00de(a)z4g2000yqa.googlegroups.com>, zigbee(a)libero.it says...
> Hi guys, thanks for your valuable answers.
>
> I would like to summarize what was said so far:
>
>
......
>
> I read carefully how the "SmartTweezers" measures the values of
> components and realized that's exactly what I need.

Without reading it properly.

It works on components NOT ASSEMBLED TO THE BOARD.

> Look at page 3 of: http://www.circuitcellar.com/archives/viewable/221-Bachiochi/Bachiochi-221.pdf
> The current flowing into the DUT returns to the voiltage source,
> passing through the virtual ground of an OP AMP. That's how they
> measure the current.
> I don't think it takes a genius to build a similar circuit.

.....

> I bet 100 $ that the SmartTweezers are able to measure'm all :-)

The IMPORTANT part you did not read and understand, which shows signs
of not understanding basic circuit theory -

"You don?t have to remove and
replace a part because you don?t know
if it?s the right part. This goes a long
way in reducing stress, especially
when a circuit is not working correctly.
Of course, you need to know how
the component is connected in the circuit
to determine if its measured value
is being affected by the surrounding
components."

The sentence starting "Of course.." is the bit everyone has told you
about and you are not listening to. This is on Page 6 of the PDF right
hand column.

When you show signs of understanding that, then we might believe you
stand a chance.

--
Paul Carpenter | paul(a)pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/> PC Services
<http://www.pcserviceselectronics.co.uk/fonts/> Timing Diagram Font
<http://www.gnuh8.org.uk/> GNU H8 - compiler & Renesas H8/H8S/H8 Tiny
<http://www.badweb.org.uk/> For those web sites you hate
From: Enrico on 9 Mar 2010 15:32
Hi,


> Which depends on circuit configuration on how accurately you can
> measure them and how long the measurements take.

One measure per second would be good.


> You still do not show basic circuit theory for when two impedances
> are in parallel (even if you are not aware of that impedance).

I spoke to an ATE expert and he told me:

When the impedance is complex, that is R//C or R//L or any other
combination, there are many approaches possible.
The real part of the impedance, that is R, could be measured applying
a constant voltage and wait for some time.
Another method to get R and C is applying a sine voltage ad a certain
frequency and measure the sine current and then get the phase
difference and the attenuation.

> You do not show any understanding about time of measurements
> for parallel capacitances (intentional or remainder of circuit).

The ATE expert told me:
there's no way to distinguish 2 capacitors in parallel. The ATE system
will always measure the sum of the two.



> How are you going to determine a diode polarity if the diode
> is a commutating or flyback diode across the relay coil?

First of all, during In-circuit test, the board is powered off,
therefore no voltage comes from the mains.
In Flyback power supplies, the diode is not in parallel to the coil.
In parallel to the coil I have an RCD clamping network therefore the
diode's nodes can be accessed by 2 nails.


> How are you going to determine the value of one resistor with
> another resistor in parallel?

The ATE expert told me:
there's no way to distinguish 2 resistors in parallel. The ATE system
will always measure the parallel of the two.

In certain cases the surrounding circuitry can be "GUARDED", that
means that using a third or a fourth probe you can isolate the Device
Under Test from the surrounding circuitry. Take a look at the
following 2 documents:

1) SCHEIBER, S. F. (2001) Building a Successful Board-Test Strategy
pages 62-63

2) US Patent 4774455 - Method for automatic guard selection in
automatic test equipment
http://www.patentstorm.us/patents/4774455/description.html

> How long are you going to wait for a resistance measurement?
one measure per second

> How will measure a circuit that has a bleed resistor across it?
> Or for that matter the bleed resistor, not uncommon for very
> large capacitors or other charge storing circuits.

The ATE expert told me:
large capacitors are measured by injecting a constant current, for
some time and sampling the voltage.
The voltage is allowed to rises up to 200 mV for not powering up the
surrounding circuitry.
By using the equation: ic = C (dV/dt) one can get the value of the
capacitor.

One can even test if the capacitor is correctly oriented (I still
don't know how)

> To what accuracy (percentage) are you expecting to measure the
> components?

The SmartTweezers measures are accurate, take a look at the specs.
I expect to get the same level of accuracy.


> The IC's and connectors may exhibit parallel loads to your
> testing (let alone shorts).

ATE systems never power up the surrounding circuitry. Some Teradyne's
documents state the measuring voltage must be in the range of +/- 200
mV


> You show little knowledge of basic circuit theory to believe you
> actually understand the simple points everyone has put to you in
> the past, and are just looking for the cheapest solution and
> believing it will work without understanding.

I'm trying to save 20.000 USD :-)





>> I read carefully how the "SmartTweezers" measures the values of
>> components and realized that's exactly what I need.

>Without reading it properly.
> It works on components NOT ASSEMBLED TO THE BOARD.

The specs say that it may work even on parts assembled on the board.
It may fail because the "SmartTweezers" are not a portable ATE system
and because they are software programmed to accomplish certain tasks.
In my case, the hardware and the software is under my control.


> The IMPORTANT part you did not read and understand, which shows signs
> of not understanding basic circuit theory -

This is my Linkedin profile: http://it.linkedin.com/in/enricomigliore

ciao,
Enrico
From: Paul Carpenter on 9 Mar 2010 20:23
In article <6c083770-26e0-416b-a854-
d81d4b0778a6(a)g19g2000yqe.googlegroups.com>, zigbee(a)libero.it says...
> Hi,
>
>
> > Which depends on circuit configuration on how accurately you can
> > measure them and how long the measurements take.
>
> One measure per second would be good.
>
>
> > You still do not show basic circuit theory for when two impedances
> > are in parallel (even if you are not aware of that impedance).
>
> I spoke to an ATE expert and he told me:
>
> When the impedance is complex, that is R//C or R//L or any other
> combination, there are many approaches possible.
> The real part of the impedance, that is R, could be measured applying
> a constant voltage and wait for some time.
> Another method to get R and C is applying a sine voltage ad a certain
> frequency and measure the sine current and then get the phase
> difference and the attenuation.
>
> > You do not show any understanding about time of measurements
> > for parallel capacitances (intentional or remainder of circuit).
>
> The ATE expert told me:
> there's no way to distinguish 2 capacitors in parallel. The ATE system
> will always measure the sum of the two.

You had to speak to an expert to work that one out?

> > How are you going to determine a diode polarity if the diode
> > is a commutating or flyback diode across the relay coil?
>
> First of all, during In-circuit test, the board is powered off,
> therefore no voltage comes from the mains.
> In Flyback power supplies, the diode is not in parallel to the coil.
> In parallel to the coil I have an RCD clamping network therefore the
> diode's nodes can be accessed by 2 nails.

You missed the word IF in the sentence, just because one board is
OK, others may not be as there may be other impedances in parallel
to a diode.

> > How are you going to determine the value of one resistor with
> > another resistor in parallel?
>
> The ATE expert told me:
> there's no way to distinguish 2 resistors in parallel. The ATE system
> will always measure the parallel of the two.

You had to speak to an expert to work that one out?

.....

> > To what accuracy (percentage) are you expecting to measure the
> > components?
>
> The SmartTweezers measures are accurate, take a look at the specs.
> I expect to get the same level of accuracy.

So you have not specifed your requirements first?

> > The IC's and connectors may exhibit parallel loads to your
> > testing (let alone shorts).
>
> ATE systems never power up the surrounding circuitry. Some Teradyne's
> documents state the measuring voltage must be in the range of +/- 200
> mV

So, I have seen all sorts of loading even at those loads, as some pins
of devices were actually a low impedance (< 500R in some cases <10R),
which need very little to affect the measurement.

The measurement is IC type specific. 200mV will not power up logic
chips, but CAN be affected by various analog or mixed signal devices.

--
Paul Carpenter | paul(a)pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/> PC Services
<http://www.pcserviceselectronics.co.uk/fonts/> Timing Diagram Font
<http://www.gnuh8.org.uk/> GNU H8 - compiler & Renesas H8/H8S/H8 Tiny
<http://www.badweb.org.uk/> For those web sites you hate
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