Intermittent responses from HP DMM

[hrsnblm]

I have a test stand that runs VB6 and is communicating to a HP-34970A DAQ via the NI PCI-GPIB. This is a set-up that has been working for years and now when it is taking a specific reading it is way out. We are reading off of channel 201, it is a resistance measurement that should be in excess of 100MOhms. When we get the intermittent reading it is around 200Ohms. We have tried all the obvious replacements, with no positive results. This includes testing with NO connection to the circuit. I have attached a portion of the NI-SPY files that relate directly to both the good & bad readings. Since I am not a GPIB expert, I was hoping someone could point me in the right direction.

Any and all assistance would be extremely appreciated.

Thank you

[Kaitlin-N]

Hi hrsnblm, 

Can you tell me more about how your system is setup and the replacements you have tried? For eaxmple, how exactly are you reading this measurement?  Are you outputting from the PCI-GPIB and reading resistance with the DMM? Has anything changed in your system from the last time it worked?

[hrsnblm]

This is a production test set-up that we have been using for many years. Recently it was shut-down (production stoppage) and the whole test station was moved about 20' in the facility. It has not worked since. However, when the stand was moved, only facility air/power was disconnected. In other words, no equipment cabling/fixtures/CTE was disconnected or changed.

Via a desktop PC, running the VB6 executable we test out our UUT. The VB6 uses the GPIB board to communicate with the HP-34970A DAQ/DMM & an HP power supply. Signals are routed to the DAQ/DMM via hard-wires from the stand and the GPIB is performing set-up in the DAQ/DMM and taking readings from the DAQ/DMM which are then routed back to the VB6 executable.

I'm not sure what other information you require, but please let me know. The NI-SPY files I've attached are from the exact same test set-up, with the same UUT, just at different times when it passed, and then failed. The way in which the tests were performed are identical (i.e., sequencing, etc).

Thank you for your help.

[nyc_(is_out_of_here)]

Do you have another HP-3970A DAQ/DMM unit to try with?

Are you sure that the connections on the DAQ board haven't come loose or something is shorting on that DAQ board?

[hrsnblm]

I should have mentioned this previously; the DMM and its cards have been replaced, the NI-GPIB card has been repleced, the PC has been replaced, the test harness and its associated connectors have been replaced. We have performed isolation testing on several points of interests. None these items has fixed the problem.

I guess one of my original questions/concerns is why the difference between the two SPU files? What do these represent and what could they possibly mean?

Thanks for your interest. If you have any aother questions, please let me know.

[nyc_(is_out_of_here)]

What does the instrument itself report to be the value, ie what is displayed on its front panel?

[hrsnblm]

Thanks everyone for your responses. The problem we were having has been rectified and turns out was not totallly an electrical problem but a hydraulic problem that caused stray parallel resitance, which caused my tests to fail. However, I never got a clear answer as to what the differences between the "Good" & "Bab" SPY files represented. If someone get the opportunity to look at these files and can explain what the differences are, and possibly why, I would greatly appreciate it.

Thank you again.

[Kaitlin-N]

Hi hrsnblm,

I received an error when trying to to open your IO Trace files. 

Here is a document that shows how to make a good IO Trace for debugging:

http://digital.ni.com/public.nsf/allkb/282C5D41E2BA04F2862574BA007803B9

Thanks,