DMM Error -1074118625, PXI DMM 4071, 4065 fails where other DMM works OK

[joma]

Dear All,

we are facing a problem with our DMM measurements. Both NI DMM 4065 and 4071 exhibit the same error: 

NI DMM Error -1074118625: Volt-Hz Common Mode Limit Has Been Exceeded

We found a KB about this: 

http://digital.ni.com/public.nsf/allkb/A593DEBFD86A69C68625727900748EEC?OpenDocument

and installed the ferrit choke as suggested in the KB. No success. 

We then took a 3rd party Keysight dmm, and was able to measure without issues. Next, we took a handheld Fluke DMM, and measured without issues. We also tried with a low cost NI USB 6009, and measured without issues (Notebook was not connected to mains).

The connection diagram is attached. We have a PS APT 7004 powering up DUT with 230 VAC. DUT controls a 3 phase motor (i.e acts as an inverter), 320V. We measure voltage drop on shunt resistor on V and U lines (we mux). PS, DUT, PXI, DMM are all in one rack (tester). 

I believe we must be doing something substantially wrong with the system setup, otherwise I could not explain the fact, that all other devices work, and the 2 NI DMM cards drop error during read. (we tried both soft panel and LV code).

I would kindly ask for any suggestion we might try out. Each help though is highly appreciated.

Thank you very much.

Regards,

Mark

[Bumblebee_Tuna]

Hi Mark,

Thank you for the description. Does the error still occur if you are not multiplexing? Have you tried using an oscope to measure the signal between the DMM and DUT?

Thanks,

Jayk

[joma]

Hi Jayk,

the problem persists. We did a scope measurement, I have attached a screenshot. The really interesting thing is, that a much lower class 3rd party dmm works fine.

Thanks a lot for any ideas / troubleshooting.

Best regards,

Mark

[joma]

The problem is present without MUX as well.

[Bumblebee_Tuna]

It's possible that the sampling rate on the other devices is too slow to capture the transience. You could try adding a low pass filter to the circuit to get rid of the transience. I've attached a link to an example of such a filter.

Also check out this link on noise suppression. There is a circuit at the bottom that might be helpful.

http://www.murata.com/~/media/webrenewal/products/emc/emifil/knowhow/26to30.ashx

-Jayk