4070 100MOhms Range

[zener_diode]

When I select the the 100MOhm range on a PXI 4070 it reads 10Megs when open circuit. It does this on the front panel and in labWindows.

If I apply 10MOhms to the input it measures 5MOhms (two 10Ms in parallel). It seems that the 4070 is setting up for 100MOhms but not doing the calculation to determine Rx. Any ideas ?

[Now_With_Underscores]

Hey Zener Diode,

Do you correctly measure 10MOhms when you're in the 10MOhm range, or do you still read 5MOhms?

Back in the 100MOhm range, what happens if you add 20MOhms? Do you see 10MOhm or 6.66MOhms?

Can you clarify that with all leads removed from the DMM front panel, setting the DMM Soft Front Panel to the 100MOhm Range results in a reading of 10MOhm?  If so, this is not expected behavior and you most likely need to send in the module for service. 

[zener_diode]

Hi John,

The instrument reads 10MOhms resistor correctly on the 10MOhm range, it indicates over range with nothing connected. 

On the 100MOhms range with nothing connected it indicates 10MOhms. Apply 10MOhms it indicates 5MOhms (ie 10MOhms in parallel with 10MOhms), apply 20MOhms it indicates 6.66MOhms (ie 10MOhms in parallel with 20MOhms) etc.

At this link http://zone.ni.com/devzone/cda/tut/p/id/3981 there is a section entitled ‘Measuring on the 100 MO Range’ which does show a 10MOhms resistor in place on the 100MOhm range. It’s as if the DMM is setting up for 100MOhm range but not doing the calculation to determine Rx.

FYI, the DMM has previously read correctly on the 100MOhm range, we were carrying out the verification procedure on it and were re-testing the resistance ranges when this problem occurred.

[Now_With_Underscores]

Hey Zener Diode,

Thanks for the additional information.  You are correct that we place a 10MOhm resistor across our output (to reduce noise) when we're in the 100MOhm range.  Our DMM then performs the intermediate math - Rdut=-10E6*Rmeas/(Rmeas-10E6) - required to determine the parallel DUT resistance, but from what you've described thus far, this doesn't appear to be happening. 

Do you have other 4070 DMMs that also exhibit this issue?  What version of NI-DMM are you using?  I verified that the incorrect behavior you descibe does not occur with any recent version of NI-DMM, but I'd like to check the version you're using, too.  

[zener_diode]

Hi John,

We do not have any other 4070 DMMs to try and we only have one PXI chassis so we cannot try it in another chassis.

We were using NI-DMM 2.8 when the problem occurred. We have upgraded to 3.02 and the problem still exists.

It’s as if something’s got set (in the DMM or the driver) that needs to be undone that issuing an niDMM_reset() or power cycling does not clear.

[Now_With_Underscores]

Hey Zener,

Thanks for the driver information; thanks for trying 3.0.2.  One last thing I would try is to run the simple resistance example located at:

C:\Program Files\National Instruments\LabVIEW 2009\examples\instr\niDMM\Single Measurements\Measure Resistance (2 or 4-wire).vi 

If that example returns the same incorrect values, then we'll need to RMA the module for service.  You can setup an RMA at (800) 531-5066

[zener_diode · Accepted solution]

Looks like we'll have to return it for repair !

Thanks