Micro-Ohms measurement

[DavidLee]

Hello,

Want to measure resistance value ,range from 0.2~0.7 milli-ohms , which board or card can be used? what method should be applied ? Your advise is greatly appreciated .

David

[DOC-doc]

You have to use half or full bridge of resistance to measure this kind of resistance value. It is the method to read strain gage and stuff like that.

Is it absolute value you want (much more difficult) or relative (change over time or other variables)

[johnsold]

Unless the device can handle large currents (amperes), look into an instrument designed for such measurements. Keithley Instruments, among others, makes such equipment. Buy a good instrument with GPIB or Ethernet interface and LV drivers. It will simplify your life a lot.

The method of choice in that range is a four-terminal measurment. The test current is applied through on pair of terminals and the voltage is measured across the other pair. If the test current is in the milliampere range the voltage is microvolts or less. The noise, thermocouple effect, and drift issues involved in making accurate measurments in that regime are best left to those with lots of expertise.

I have been an instrumentation engineer for >20 years and I would not attempt to ma
ke that kind of measurement except by obtaining a suitable instrument. I have no connection with any manufacturer of this equipment.

Lynn

[tbob]

I have no connection to Keithley, but I agree with Lynn that Keithley makes such equipment. Having used Keithley instruments in the past, I highly recommend them for any small but accurate measurements, such as microvolts, microamps, and milliohms.

[Aname]

davidLee wrote in news:5065000000080000005BFF0000-
1079395200000@exchange.ni.com:

> Hello,
>
> Want to measure resistance value ,range from 0.2~0.7 milli-ohms ,
> which board or card can be used? what method should be applied ? Your
> advise is greatly appreciated .
>
> David

I agree with all the other posters, don't try to make a millohm meter
from scratch.

HP (called Agilent now) makes a low priced millohm meter (around
$1100.00) you might want to check out. Its a four wire multimeter with a
lot of resolution.

Here's the link to their selection guide. If price is a concern, these
are about the cheapest I have been able to find.

Not an HP or Agilent person, just been down the milliohm meter road
before.

http://we.home.agilent.com/upload/cmc
_upload/All/DMM3.html

JT