Multiplexed resistance meter
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Posts: 46,084
Hi, I would like to make an automated test equipment to be used for
measuring resistance of kelvin contactors.
there ar 15 contactors so I want to measure the resistance of each
contactors which is less than 1 Ohm. I will conduct a pin to pin
measurement and a pin to ground measurement to check if the pins are
grounded.
Any ideas if how i can make this possible? The resistance involved is
less than 1 Ohm.
Thanks you.
measuring resistance of kelvin contactors.
there ar 15 contactors so I want to measure the resistance of each
contactors which is less than 1 Ohm. I will conduct a pin to pin
measurement and a pin to ground measurement to check if the pins are
grounded.
Any ideas if how i can make this possible? The resistance involved is
less than 1 Ohm.
Thanks you.
Comments
I built a similar piece of test equipment a few years
back. It was an automated power supply tester, but was
very complex and used a PC and VisualBasic instead of
a Stamp.
I used a GPIB equipped DMM for the measuring portion
of the project. I then built a multiplexor system with
high-quality relays to direct the desired measurement
at the appropriate time to the DMM. The relays were
driven by a digital I/O PCI card, and the GPIB
interface was a PCI card too.
The program would increment the relay, hold it, take a
measurement with the DMM, store the value, increment
to the next relay, and so on. Once the sequence was
complete, the list of values was compared for accuracy
and the results displayed to an operator who passed or
failed the power supply.
My program was designed to be quick and very automated
so as not to require a skilled operator. The operator
installed ten power supplies in bays one through ten,
and pushed start. Three minutes later, the operator
was instructed to pass or fail certain slots and
continue.
If you are looking for something relatively slow, you
may be able to skip the GPIB and PCI section and
simply have a Stamp increment a relay matrix,
connected to a DMM, each time a button is pressed. The
operator (or yourself) would push the button, read the
DMM (one with low resistance capabilities, or course),
and press the button again, read it again, and so on.
Cool project.
Regards,
Dr. Diode
--- catcat <semiconductor@p...> wrote:
> Hi, I would like to make an automated test equipment
> to be used for
> measuring resistance of kelvin contactors.
>
> there ar 15 contactors so I want to measure the
> resistance of each
> contactors which is less than 1 Ohm. I will conduct
> a pin to pin
> measurement and a pin to ground measurement to check
> if the pins are
> grounded.
>
> Any ideas if how i can make this possible? The
> resistance involved is
> less than 1 Ohm.
>
> Thanks you.
>
>
> To UNSUBSCRIBE, just send mail to:
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> from the same email address that you subscribed.
> Text in the Subject and Body of the message will be
> ignored.
>
>
> Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
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using a relay to measure relay contact resistance of another relay, even
though the selecting relay is high quality it doesn't sound good.
Is there a non mechanical solution anyone can see.
I'm working on a similar project and I worry about relay noise (clicking)
and relay life if you wanted to do continues monitoring.
<snips>
>
> The program would increment the relay, hold it, take a
> measurement with the DMM, store the value, increment
> to the next relay, and so on. Once the sequence was
> complete, the list of values was compared for accuracy
> and the results displayed to an operator who passed or
> failed the power supply.
> Regards,
> Dr. Diode
Bridge, which nulls out the resistance of the test leads themselves. That
way you can accurately measure resistance to below 0.1 ohms without having
to resort to jumper cables for test leads. It does this by comparing the
test resistance to a switchable bank of know-value resistors, and when the
needle in the meter nulls, the test resistance equals the comparison
resistance. We used this method to test and select resistors down to a few
ppm (parts per million) accuracy. If you need to switch banks of test
subjects, just use standard 4-pole relays.
Mike Sokol
www.modernrecording.com
mikes@m...
Original Message
From: "Richard Furniss" <rfurniss@e...>
To: <basicstamps@yahoogroups.com>
Sent: Sunday, August 10, 2003 12:56 PM
Subject: Re: [noparse][[/noparse]basicstamps] Multiplexed resistance meter
> Your right this is a cool project, the only problem I see is that you are
> using a relay to measure relay contact resistance of another relay, even
> though the selecting relay is high quality it doesn't sound good.
>
> Is there a non mechanical solution anyone can see.
>
> I'm working on a similar project and I worry about relay noise (clicking)
> and relay life if you wanted to do continues monitoring.
>
> <snips>
> >
> > The program would increment the relay, hold it, take a
> > measurement with the DMM, store the value, increment
> > to the next relay, and so on. Once the sequence was
> > complete, the list of values was compared for accuracy
> > and the results displayed to an operator who passed or
> > failed the power supply.
>
> > Regards,
> > Dr. Diode
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
avoiding.
--- In basicstamps@yahoogroups.com, PH <drdiode2002@y...> wrote:
> Hello,
>
> I built a similar piece of test equipment a few years
> back. It was an automated power supply tester, but was
> very complex and used a PC and VisualBasic instead of
> a Stamp.
>
> I used a GPIB equipped DMM for the measuring portion
> of the project. I then built a multiplexor system with
> high-quality relays to direct the desired measurement
> at the appropriate time to the DMM. The relays were
> driven by a digital I/O PCI card, and the GPIB
> interface was a PCI card too.
>
> The program would increment the relay, hold it, take a
> measurement with the DMM, store the value, increment
> to the next relay, and so on. Once the sequence was
> complete, the list of values was compared for accuracy
> and the results displayed to an operator who passed or
> failed the power supply.
>
> My program was designed to be quick and very automated
> so as not to require a skilled operator. The operator
> installed ten power supplies in bays one through ten,
> and pushed start. Three minutes later, the operator
> was instructed to pass or fail certain slots and
> continue.
>
> If you are looking for something relatively slow, you
> may be able to skip the GPIB and PCI section and
> simply have a Stamp increment a relay matrix,
> connected to a DMM, each time a button is pressed. The
> operator (or yourself) would push the button, read the
> DMM (one with low resistance capabilities, or course),
> and press the button again, read it again, and so on.
>
> Cool project.
>
> Regards,
> Dr. Diode
> --- catcat <semiconductor@p...> wrote:
> > Hi, I would like to make an automated test equipment
> > to be used for
> > measuring resistance of kelvin contactors.
> >
> > there ar 15 contactors so I want to measure the
> > resistance of each
> > contactors which is less than 1 Ohm. I will conduct
> > a pin to pin
> > measurement and a pin to ground measurement to check
> > if the pins are
> > grounded.
> >
> > Any ideas if how i can make this possible? The
> > resistance involved is
> > less than 1 Ohm.
> >
> > Thanks you.
> >
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> > from the same email address that you subscribed.
> > Text in the Subject and Body of the message will be
> > ignored.
> >
> >
> > Your use of Yahoo! Groups is subject to
> > http://docs.yahoo.com/info/terms/
> >
> >
>
>
> __________________________________
> Do you Yahoo!?
> Yahoo! SiteBuilder - Free, easy-to-use web site design software
> http://sitebuilder.yahoo.com
relays.
--- In basicstamps@yahoogroups.com, "Richard Furniss" <rfurniss@e...>
wrote:
> Your right this is a cool project, the only problem I see is that
you are
> using a relay to measure relay contact resistance of another relay,
even
> though the selecting relay is high quality it doesn't sound good.
>
> Is there a non mechanical solution anyone can see.
>
> I'm working on a similar project and I worry about relay noise
(clicking)
> and relay life if you wanted to do continues monitoring.
>
> <snips>
> >
> > The program would increment the relay, hold it, take a
> > measurement with the DMM, store the value, increment
> > to the next relay, and so on. Once the sequence was
> > complete, the list of values was compared for accuracy
> > and the results displayed to an operator who passed or
> > failed the power supply.
>
> > Regards,
> > Dr. Diode
--- In basicstamps@yahoogroups.com, "Mike Sokol - ModernRecording"
<mikes@m...> wrote:
> For very low-resistance measurement, a good way to go is a 4-wire
Kelvin
> Bridge, which nulls out the resistance of the test leads
themselves. That
> way you can accurately measure resistance to below 0.1 ohms without
having
> to resort to jumper cables for test leads. It does this by
comparing the
> test resistance to a switchable bank of know-value resistors, and
when the
> needle in the meter nulls, the test resistance equals the comparison
> resistance. We used this method to test and select resistors down
to a few
> ppm (parts per million) accuracy. If you need to switch banks of
test
> subjects, just use standard 4-pole relays.
>
> Mike Sokol
> www.modernrecording.com
> mikes@m...
>
>
>
Original Message
> From: "Richard Furniss" <rfurniss@e...>
> To: <basicstamps@yahoogroups.com>
> Sent: Sunday, August 10, 2003 12:56 PM
> Subject: Re: [noparse][[/noparse]basicstamps] Multiplexed resistance meter
>
>
> > Your right this is a cool project, the only problem I see is that
you are
> > using a relay to measure relay contact resistance of another
relay, even
> > though the selecting relay is high quality it doesn't sound good.
> >
> > Is there a non mechanical solution anyone can see.
> >
> > I'm working on a similar project and I worry about relay noise
(clicking)
> > and relay life if you wanted to do continues monitoring.
> >
> > <snips>
> > >
> > > The program would increment the relay, hold it, take a
> > > measurement with the DMM, store the value, increment
> > > to the next relay, and so on. Once the sequence was
> > > complete, the list of values was compared for accuracy
> > > and the results displayed to an operator who passed or
> > > failed the power supply.
> >
> > > Regards,
> > > Dr. Diode
> >
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> > from the same email address that you subscribed. Text in the
Subject and
> Body of the message will be ignored.
> >
> >
> > Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
> >
> >
http://newton.ex.ac.uk/teaching/CDHW/Sensors/#Resistance. Typically, a
Kelvin bridge is used to compare a group of test resistors against a
"standard resistor" to within a great degree of accuracy. This accuracy can
be gained up or down at the sensing amplifier which drives the null meter.
This "standard" resistor is normally calibrated against a known resistance
value that's traceable to the National Bureau of Standards. Since you're
only worried about nulling, the exact voltage used in the circuit doesn't
really matter, and the exact sensitivity of the null meter doesn't matter
either. Once you get zero current, the two resistor values must be equal.
And you can add really long sense leads or insert things like relay
contacts, and the circuit will still compare resistances properly. The
disadvantage of a standard ohm meter type circuit is that it can be
uncalibrated by any serial lead resistance, as well as the exact voltage
applied across the test resistor, all of which is difficult to calibrate and
verify to Government standards.
Mike Sokol
www.modernrecording.com
mikes@m...
Original Message
From: "catcat" <semiconductor@p...>
To: <basicstamps@yahoogroups.com>
Sent: Monday, August 11, 2003 5:19 AM
Subject: [noparse][[/noparse]basicstamps] Re: Multiplexed resistance meter
> Hi, can you gice a schematic of the circuit. Thanks.
>
> --- In basicstamps@yahoogroups.com, "Mike Sokol - ModernRecording"
> <mikes@m...> wrote:
> > For very low-resistance measurement, a good way to go is a 4-wire
> Kelvin
> > Bridge, which nulls out the resistance of the test leads
> themselves. That
> > way you can accurately measure resistance to below 0.1 ohms without
> having
> > to resort to jumper cables for test leads. It does this by
> comparing the
> > test resistance to a switchable bank of know-value resistors, and
> when the
> > needle in the meter nulls, the test resistance equals the comparison
> > resistance. We used this method to test and select resistors down
> to a few
> > ppm (parts per million) accuracy. If you need to switch banks of
> test
> > subjects, just use standard 4-pole relays.
> >
> > Mike Sokol
> > www.modernrecording.com
> > mikes@m...
> >
> >
> >
Original Message
> > From: "Richard Furniss" <rfurniss@e...>
> > To: <basicstamps@yahoogroups.com>
> > Sent: Sunday, August 10, 2003 12:56 PM
> > Subject: Re: [noparse][[/noparse]basicstamps] Multiplexed resistance meter
> >
> >
> > > Your right this is a cool project, the only problem I see is that
> you are
> > > using a relay to measure relay contact resistance of another
> relay, even
> > > though the selecting relay is high quality it doesn't sound good.
> > >
> > > Is there a non mechanical solution anyone can see.
> > >
> > > I'm working on a similar project and I worry about relay noise
> (clicking)
> > > and relay life if you wanted to do continues monitoring.
> > >
> > > <snips>
> > > >
> > > > The program would increment the relay, hold it, take a
> > > > measurement with the DMM, store the value, increment
> > > > to the next relay, and so on. Once the sequence was
> > > > complete, the list of values was compared for accuracy
> > > > and the results displayed to an operator who passed or
> > > > failed the power supply.
> > >
> > > > Regards,
> > > > Dr. Diode
> > >
> > >
> > > To UNSUBSCRIBE, just send mail to:
> > > basicstamps-unsubscribe@yahoogroups.com
> > > from the same email address that you subscribed. Text in the
> Subject and
> > Body of the message will be ignored.
> > >
> > >
> > > Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
> > >
> > >
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
Many Digital Multimeters, like the Hp/Agilent 34401, have a 4 wire
connection for resistance in addition to the two wire connection. There
is a special set of leads for use with the Kelvin connection. The 34401
reads out to 0.000,1 Ohms. The 4 wire, Kelvin, connection is very
simple. One of the pairs has a current source and the other pair is a
voltmeter. Suppose that all 4 wires had 10 Ohms of resistance and you
want to measure a 1 Ohm resistor using a 1 ma current source.
If you used a 2 wire Ohm meter then 1 ma * 1 Ohm is 1 mv, but the leads
contribute 2 * 10 Ohms * 1 ma = 20 mv of error. You could try to use
the delta DMM function by shorting the leads and pressing zero, but the
lead resistance may vary as the leads are moved making it impossible to
measure a resistance that's much smaller than the lead resistance. The
contact resistance may also be greater or equal to the resistance of the
device you're trying to measure.
For a 4 wire, Kelvin, connection: The resistance in the voltmeter leads
has an insignificant effect since the Voltmeter input impedance is 10
Meg Ohms. Since the meter is connected on the device side of the lead
resistance in the current pair that voltage drop is not seen by the
voltmeter. The voltmeter ends up reading 1 mv. Note that if there is
contact resistance and the voltmeter is connected closer to the DUT than
the current pair the contact resistance will also be removed from the
measurement. Also note that it really doesn't matter what the lead +
contact resistance is, it will be removed from the measurement as long
as the current source has the compliance to keep supplying the same
current even though the voltage gets large.
By measuring an accurately known resistor using the Kelvin connection
you can determine the scale factor (calibration of both the current
source and the voltmeter). This could then be used to improve the
overall accuracy of the system.
You can make your own current source from one of the National
Semiconductor 3 lead temperatures sensors, a diode, as a few other
parts. Use that with an A/D converter on the BS and you have a Kelvin
measuring system. You could use DPST relays, but there are solid state
switches that could also be used and the on resistance spec is not
critical in the case of a Kelvin connection.
Have Fun,
Brooke CLarke, N6GCE
>
Original Message
>From: "catcat" <semiconductor@p...>
>To: <basicstamps@yahoogroups.com>
>Sent: Monday, August 11, 2003 5:19 AM
>Subject: [noparse][[/noparse]basicstamps] Re: Multiplexed resistance meter
>
>
>
>
>>Hi, can you gice a schematic of the circuit. Thanks.
>>
>
>
cancels out any battery effects which result when dissimilar metals make
contact. You really can measure resistances down to a tiny fraction of an
ohm with the proper equipment.
And as a side note, on a previous job we used a Kelvin bridge setup to
measure spinning resistors sealed inside tiny glass tubes filled with Argon
gas, which we would Laser trim to within 100 ppm of a target value. It was
pretty cool....
Mike Sokol
Original Message
From: "Brooke Clarke" <brooke@p...>
To: <basicstamps@yahoogroups.com>
Sent: Tuesday, August 12, 2003 1:13 PM
Subject: [noparse][[/noparse]basicstamps] Multiplexed resistance meter
> Hi Cat Cat:
>
> Many Digital Multimeters, like the Hp/Agilent 34401, have a 4 wire
> connection for resistance in addition to the two wire connection. There
> is a special set of leads for use with the Kelvin connection. The 34401
> reads out to 0.000,1 Ohms. The 4 wire, Kelvin, connection is very
> simple. One of the pairs has a current source and the other pair is a
> voltmeter. Suppose that all 4 wires had 10 Ohms of resistance and you
> want to measure a 1 Ohm resistor using a 1 ma current source.
>
> If you used a 2 wire Ohm meter then 1 ma * 1 Ohm is 1 mv, but the leads
> contribute 2 * 10 Ohms * 1 ma = 20 mv of error. You could try to use
> the delta DMM function by shorting the leads and pressing zero, but the
> lead resistance may vary as the leads are moved making it impossible to
> measure a resistance that's much smaller than the lead resistance. The
> contact resistance may also be greater or equal to the resistance of the
> device you're trying to measure.
>
> For a 4 wire, Kelvin, connection: The resistance in the voltmeter leads
> has an insignificant effect since the Voltmeter input impedance is 10
> Meg Ohms. Since the meter is connected on the device side of the lead
> resistance in the current pair that voltage drop is not seen by the
> voltmeter. The voltmeter ends up reading 1 mv. Note that if there is
> contact resistance and the voltmeter is connected closer to the DUT than
> the current pair the contact resistance will also be removed from the
> measurement. Also note that it really doesn't matter what the lead +
> contact resistance is, it will be removed from the measurement as long
> as the current source has the compliance to keep supplying the same
> current even though the voltage gets large.
>
> By measuring an accurately known resistor using the Kelvin connection
> you can determine the scale factor (calibration of both the current
> source and the voltmeter). This could then be used to improve the
> overall accuracy of the system.
>
> You can make your own current source from one of the National
> Semiconductor 3 lead temperatures sensors, a diode, as a few other
> parts. Use that with an A/D converter on the BS and you have a Kelvin
> measuring system. You could use DPST relays, but there are solid state
> switches that could also be used and the on resistance spec is not
> critical in the case of a Kelvin connection.
>
> Have Fun,
>
> Brooke CLarke, N6GCE
>
> >
Original Message
> >From: "catcat" <semiconductor@p...>
> >To: <basicstamps@yahoogroups.com>
> >Sent: Monday, August 11, 2003 5:19 AM
> >Subject: [noparse][[/noparse]basicstamps] Re: Multiplexed resistance meter
> >
> >
> >
> >
> >>Hi, can you gice a schematic of the circuit. Thanks.
> >>
> >
> >
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>