10-28-2014 06:44 AM
Hi,
I I would like to measure a componant that have a 3-5 Ohm resistance.
Change in the resistance value during my experiment is 0.003 Ohm.
Using DMM is not prefered becouase it has only 1 channel and i don't want to use switching card in addition to the DMM.
So I m looking for the correct modules selection that will allow me to measure the resistance change using 4 probe methood.
That means a current source and analog input modules.(can be one if possible)
For this I need a stable current source and hi resolution Volt analog input modules.
the requirments are:
1) not more then 10mA current (avoid heating of the componant)
2) 8 channels (more is good).
3) sampling rate max 100 Hz can be less down to 10 Hz f it help to reduce cost.
4) Effective resolution (after accuracy,stability,offset temperature drift and noise(in the bandwith in 3) of 0.05 to 0.1 mOhm.
5) enviromental temperature where the equipment will be used is 25+- 5 degree.
I hope there a modules that can fit this requirments, if not i would be happy to know what is the nearest that possible.
I understand that PXI is the best platform for this but other platform is also possible.
Thanks.
10-28-2014 11:19 AM
10mA with 0.1mOhm resolution results in ONE µV !!
Additional thermoelectric EMV on the contacts etc....
Some ideas
-use a AC bridge configuration with a preamp .... Ups ...resistors with a tempco less than 10ppm/K !!
-ask Keithley 😉 , sorry NI
- a XXmA two pole current 'diode' (maybe in an appnote from Jim Williams 🙂 ) in a 4 diode bridge sourced by a +- squarewave supply , building an alternating current source, and a differential preamp ... the pream is per channel , the rest might be done with muxer
did I mention 4 wire measurements?? 😄
10-28-2014 02:30 PM
10-28-2014 02:57 PM
Well maybe you measured changes in the 0.1mOhm region, and I don't know your setup, but you can't beat physics 😉
Make a shortcut as good as you can at your DMM and measure the the voltage .... what do you read?
10-28-2014 03:23 PM