Auto randing issue and looking for Status attribute for PXI 4072 DMM

[Crymsenn]

I have a 4072 and some inherited code that was auto ranging the card before every measurement. Seemingly, the card returns a max reading if not enough time is allowed after the command to setup the measurement. What I am looking for is a way to monitor the card status. I would prefer monitoring the status, over just introducing a set delay like I am now, which works.

Also, the cards specs say it should auto range for a 2wire resistance measurement in 50ms, I've found it takes 200+ms for me to get consistent results.

Thank you in advance for you help!

 

[Chris_K_]

Hi Crymsenn

There is a Get Measurement Period Function that you can call that will indicate how long the configured measurements will take.  You can use this to determine how long you need to set your timeout value.

If you are using LabVIEW the is the niDMM Get Measurement Period VI or it is the niDMM_GetMeasurementPeriod.

Let me know if you have any more questions.

Regards

ChrisK

[Crymsenn]

In the mean time I found that function (using CVI). But from the way you describe it you'd use this to specify the time when requesting a read from the DMM?

I currently have the timeout set to the default, auto.

After playing with this problem some more it seems like my DMM is refusing to lock onto a range. I opened the soft panel while I had my connections made, set the dmm to auto range and measure a 2wire resistance. I could see it switch back and forth between ranges, never stopping on one. But if I specify a range it measures the resistance spot on, without any fluctuation in the number.

I checked out the lines with a scope to ensure there was not some errant signal causing the DMM to keep readjusting and it was clean.

Is it just my DMM flaking out?

P.S. Could a Mod edit my title to fix my typo... "Auto randing". I tried doing it myself, but couldn't find where to.

[Chris_K_]

What resistance value are you measuring.  Is the value between two different ranges and the DMM is having problems getting to the right one?  If you let me know what the value is I can try it here with my 4072 and if I am not seeing the same behaviour as you are.  I expect that I won't and there is something else causing the problem. 

Can you confirm all the driver versions that you are using.  It can be seen in Measurement and Automation Explorer (MAX).

[Crymsenn]

Yes, it is close to one of the "edges" between two ranges. The resistance is 100-105 ohms.

Versions:

iviDmm 3.0

iviDriver 1.0

[Paul_C.]

Hi Crymsenn,

When measuring a resistance so close between two ranges, the auto range feature will have trouble selecting the appropriate range.  The 100 Ohm range can be used if the signal is no more than 10% over the range.  So you have to be careful when trying to measure a resistance in that 10% region.  When measuring resistance values so close between two ranges it is necessary to arbitrarily select a range.

Regards,

Paul C. 

Message Edited by Paul C. on 09-17-2008 10:51 AM