How can I prevent static discharge from interfering with my AMUX-64 signals.

[Al V]

I am using an internally-powered AMUX-64T board to acquire floating thermocouple and thermopile voltages. The DAQ card is set up in the ± 10V differential mode. The AMUX is configured so that the CJ sensor is on channel 0 and the shield jumper is disconnected. I have soldered a 10 K ohm resistor from the (-) side of each differential channel to AIGND. Most of time the system works fine, but if someone touches any of the metal areas of the test fixture, the AMUX board seems to reset and the temperature values jump to very high values. If I stop the acquisition vi and restart it, everything seems fine until someone touches the fixture again. I have moved the W1 ground jumper
to the shield connected side, but this does not help. Is there something I can do to prevent this static discharge from resetting my board?

[Geneva L.]

Here are some ideas for you:

If you think the issue is static discharge, you can try using ESD control mats, ESD worksurfaces, operator ground straps, humidifiers, air ionizers and the like.


As page 3-5 of the AMUX-64T User Manual (http://www.ni.com/manuals) states

"The cold-junction compensation is accurate only if the temperature sensor
reading is close to the temperature of the screw terminals. Therefore, when
thermocouples are being read, you should keep the AMUX-64T away from
drafts or other temperature gradients such as those caused by heaters,
radiators, fans, very warm equipment, and so on."

Since you are making thermocouple measurements, that may be a factor. Also, thermocouples are not as rugged as other temperature devices and connections may not be
as secure.

I suggest stepping back to test without the thermocouples. Try grounding your inputs to read 0 V or using a battery across the differential inputs of a channel. Use the Measurement & Automation Explorer Test Panels for your DAQ board.

Regards,

Geneva L.
Applications Engineering
National Instruments
http://www.ni.com/ask