Measuring continuity

Between two/multiple nodes across connectors. The manual test spec says less than 1 Ohm. Easy, just use a milliOhm meter. The automatic test spec uses a fancy test box that costs mega bucks.(PC + endless cards +30 odd 25 way D sockets/plugs) From the test print out, it seems the test gear is measuring millivolts. This leads me to believe that they are injecting a constant current into one node, grounding another node and measuring the small voltage at the first node using an ADC(if that makes sense). I think the test gear uses generic Nat semi industrial measurement cards. Is this how any of you would expect a continuity test to be accomplised using ATE ? If not, anyone got any experience of doing this ? Typical values are in the low tens of milliohms. TIA

Reply to
TTman
Loading thread data ...

Google "four wire resistance measurement".

Any good bench DVM from HP or Fluke can do this.

tm

Reply to
tm

Yes. That would be a Kelvin connection:

formatting link

I've used it in industry to test PCB trace resistance using non-automatic tools. It would be a simple setup using a data acquisition system.

--Winston

Reply to
Winston

TTman schrieb:

Hello,

if you want to measure milliohms and even microohms, the four wire method is essential and you need a measuring current high enough to generate at least some ten to hundred microvolts over the measured resistor.

Bye

Reply to
Uwe Hercksen

ess

one

rst

eric

he

ATE's great for doing lots of tests on a board, its an expensive way of doing just one.

NT

Reply to
NT

ATE's great for doing lots of tests on a board, its an expensive way of doing just one.

Qualification.... I know about 4 wire/kelvin. There are a large number of boards with a large number of continuity checks. Hence the ATE route. This route precludes the use of 4 wire. The accuracy is unimportant, 10%,20% is no problem. The spec is simply that is must be

Reply to
TTman

(...)

Clarification, please?

If you now "measure typically low tens of milliohms" with acceptable precision, accuracy and repeatability using your ATE, and you need to resolve only to ~ 780 mOhms +- 20 mOhms, what is the problem?

If your ATE cannot now provide that level of precision, accuracy and repeatability, Kelvin is your only choice.

Bed of nails or 'flying probe'?

formatting link

'Bed of nails' Kelvin is possible if you have a tame machinist on staff. 'Flying Probe' Kelvin is a bit of a challenge but quite possible if you can spin the PCB to accommodate testability.

:)

--Winston

Reply to
Winston

I'd like to replicate what the ATE does, which is provide a reasonable measurement of the contact resistances. From a test board with various connectors, there are cables connecting to a PC using regular wires and connectors. I can only assume that they use a 'group' resistance in their calculations that are representative of the overall resistance and subtract that from measurements..... Our company uses a mixture of technologies- Takaya flying probe machines, bed of nails ( which does reasonable milliohm contact resistances) and this other archaic machine.... I agree, resolving continuity to 1 ohm is easy, but I'd like a better( more accurate) solution. None of our current machies fit this particular project because of the large setup costs. We also have a Cirrus system running 4 blocks which could be a solution.....All of these ( except Takaya maybe) are

2 wire systems.... It looks like one solution would be to use high side current sense circuits, fed by a constant current source and a load dump to ground. Seems feasable to me ?
Reply to
TTman

(...)

Kelvin is your answer then. See the link at the bottom of this page!

Tailor your maximum forcing voltage to be well below the saturation threshold of your lowest semiconductor and read your resistance as the voltage drop divided by the constant current. This meter is really nice, for example. (100 uV forcing voltage, max.)

formatting link

(...)

When I last looked into this, I was checking out *coaxial* pogo pins. You get two contacts for the price of one, theoretically.

And look at this! They actually exist now!

formatting link

Note that just about everybody else calls their spring loaded contacts 'coaxial' but they are still only one contact per channel.

--Winston

Reply to
Winston

=20

precludes=20

The=20

with 2

the

to a=20

=20

uses=20

archaic=20

more=20

project=20

=20

are=20

circuits,=20

feasable=20

You may be in for some reverse engineering here. There is another = variant that i have seen, to place many board runs in series and then measure the differential voltages at successive connection pairs. Kind of like this:

Current Measurement Selector Source Points "Relays"

------------------+----------------------------------- X |=20 ^ contacts / connectors ^ | v1 R trace | ^ contacts / connectors ^ |__________________________________ X | ^ contacts / connectors ^ | v2 R trace | ^ contacts / connectors ^ |___________________________________ X | ^ contacts / connectors ^ | more voltages ~ ellipsis ~ |

------------------+----------------------------------- X

?-)

Reply to
josephkk

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.