Prev: beautiful indian girls see and enjoy
Next: User interface cognitive loading
From: genebren on 22 Feb 2010 19:55
Enrico,

Do yourself a great favor, buy a in-circuit tester. I will have to admit
that I am a partially biased voice on this issue, as I onced managed the
development of In-circuit test equipment (Zentel/Teradyne). I have also
had the experience of working for a company that after seeing a Zentel
product (Z1800), had decided in would be very easy to build a clone of the
product for their own testing needs. Long story short, they failed!
(several years later, and thousands poorer, they could not even test
resistors). I was very glad that I was never asked to make in work for
them.

A quick glance of the used/referbished market shows that a low-end Z1800
could be purchased for ~$18K. (I'm sure that a deeper look could find a
better deal, try ebay) In the long run this would be much cheaper, and far
more reliable than a home built unit.

With a more capable unit, you could do things like test multiple boards at
once, test with power on, maybe even gang program devices......

Good luck
Gene

---------------------------------------
Posted through http://www.EmbeddedRelated.com
From: Jim Stewart on 23 Feb 2010 13:24
genebren wrote:
> Enrico,
>
> Do yourself a great favor, buy a in-circuit tester. I will have to admit
> that I am a partially biased voice on this issue, as I onced managed the
> development of In-circuit test equipment (Zentel/Teradyne). I have also
> had the experience of working for a company that after seeing a Zentel
> product (Z1800), had decided in would be very easy to build a clone of the
> product for their own testing needs. Long story short, they failed!
> (several years later, and thousands poorer, they could not even test
> resistors). I was very glad that I was never asked to make in work for
> them.

I'm wondering why you had such a bad experience.

Years ago I was hired to solve a specific test problem
at a ballot counting company. They were unable to
align and test the optical readheads for their main
product. In one month I had a prototype working that
would give a graphical display of the mechanical alignment
of each of the 4 lens assemblies, to .001" and select
the proper resistors for gain. In three months, they
had 3 production testers. The readhead test department
went from 7 people to one. They only needed one tester,
but wanted to have a spare and a spare for the spare (:.

Given my experience, it's hard to believe that after
several years, your associates couldn't test resistors.
From: genebren on 23 Feb 2010 13:46
>genebren wrote:
>> Enrico,
>>
>> Do yourself a great favor, buy a in-circuit tester. I will have to
admit
>> that I am a partially biased voice on this issue, as I onced managed
the
>> development of In-circuit test equipment (Zentel/Teradyne). I have
also
>> had the experience of working for a company that after seeing a Zentel
>> product (Z1800), had decided in would be very easy to build a clone of
the
>> product for their own testing needs. Long story short, they failed!
>> (several years later, and thousands poorer, they could not even test
>> resistors). I was very glad that I was never asked to make in work for
>> them.
>
>I'm wondering why you had such a bad experience.
>
>Years ago I was hired to solve a specific test problem
>at a ballot counting company. They were unable to
>align and test the optical readheads for their main
>product. In one month I had a prototype working that
>would give a graphical display of the mechanical alignment
>of each of the 4 lens assemblies, to .001" and select
>the proper resistors for gain. In three months, they
>had 3 production testers. The readhead test department
>went from 7 people to one. They only needed one tester,
>but wanted to have a spare and a spare for the spare (:.
>
>Given my experience, it's hard to believe that after
>several years, your associates couldn't test resistors.
>

Jim,

I think that the biggest mistake that people make in this situtation is
that they under estimate the full scope of the job. What looks like a very
simple requirement (In-circuit connection and testing of a hand full
components) gets increasely more difficult as you get further down the
stream. What about guarding of connected component? What about charge
build up in capacitors? Further more, it was quite clear that the original
poster was not too clear about how to even test a capacitor.

I too know of people who were able to successfully build their own test
equipment. I know that sometimes it is the only way to go. But more times
that not, the time and cost of rolling your own tester will cost you more
in the long run.

In the case of the co-workers that I refered to, they completely under
estimated the task at hand. Not only that, they were far to stubborn to
realize that they were in over their heads and re-evaluate the situtation.

Gene

---------------------------------------
Posted through http://www.EmbeddedRelated.com
From: Hans-Bernhard Bröker on 23 Feb 2010 20:03
genebren wrote:

> Do yourself a great favor, buy a in-circuit tester.

I'll second that notion, but for different reasons. Bluntly put,
testing equipment shall never be built, nor designed, by the same people
who make the device under test, period.

You need different people designing the tester to avoid etting false OK
results slipping through because your home-grown tester made the same
mistakes it's supposed to be checking for. You need a different plant
to build the testing equipment to ensure that they don't both have the
same, slight mechanical ill-alignment.

Oh, and designing that test equipment requires all kinds of knowledge
that by your own admission you currently don't have. By the time you've
acquired that knowledge (and are 101% bet-the-farm-on-it _sure_ you've
got it right), it's almost certain you'll have spent more than a
turn-key solution would have cost.

Testing equipment, like all measurement devices, has to be of higher
quality than the stuff it's supposed to test, all across the board.
That's the only way you can ever tell apart actual effects from flawed
measurements. The usual way people check that condition is by telling
you to get your testing equipment from companies who are known to know
what they're doing on that front, and will vouch for calibration,
long-term stability and such. The companies in that market get to call
up the kind of prices that you consider so forbiddingly high because
their machines are worth just about every single cent.

And if, as I suspect, it's your customers' QA people that are driving
this requirement for an ICT step, either they or your liability insurer
will quite likely _insist_ that you use third-party testing gear anyway,
for all the above reasons. They simply won't believe that the results
of a tester you made for yourself are significantly more reliable than
your production process already is.

Ultimately, if your production volumes are so small that you can't seem
to justify the costs of an ICT machine, although your quality
requirements suggest you should have one, I would suggest you thoroughly
re-investigate whether you should be populating your own PCBs in the
first place. You might be better off farming that job out to
contractors --- they have ICT.
From: Enrico on 5 Mar 2010 07:43
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

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.


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

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

ciao,
Enrico




First  |  Prev  |  Next  |  Last
Pages: 1 2 3
Prev: beautiful indian girls see and enjoy
Next: User interface cognitive loading