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Shielding Grounding Triboelectricity
Avoiding trouble from triboelectric charging.
By Curt Wuollet on 12 February, 2018 - 11:59 am

Hi All

Here in Minnesota, this is the time of year where when the gremlins come out. Mysterious reboots, dead sensors, weird and wonderful new opportunities for troubleshooting. The temperature wobbles either side of zero and the indoor relative humidity plummets. So after fixing several odd problems, I thought it good to share the root cause of many.

Shielding: If you aren't going to effectively ground the shields, don't shield. In many cases, shielding that is not grounded becomes anti-shielding, that is, it makes equipment _more_ susceptible to static disruption. If I wanted to induce a voltage in a wire, the best way would be to wrap it in something metallic and zap the wrapping.

Static:
Control humidity if you can, its the cheapest way to stop the zaps.

Correlate equipment glitches with humidity, this is the time to identify what needs fixing.
Use ionizers if necessary, some web processes become extreme static generators when the humidity gets low enough. Nearby equipment may be problem children for only a couple weeks of the year, but it can drive you crazy and produce "walking wounded" failures for later fun.

Most automation equipment is really good about ESD protection, but it's easy to generate 30 or 40 thousand volts just picking up a sheet or sliding things or....... Wicked puddles of charge on good insulators can be very difficult to get rid of. Ionizers are often about the only way on a moving process.

I'm waiting for some conductive paint to ground and shield plastic enclosures and the issues seem to be slowing with the higher temps and humidity, but if you've been having gremlins just lately, maybe this is why. You guys in the tropics, never mind.

Regards
cww

Curt,

EXCELLENT reminders--all! Shield grounding is important--but effective shield grounding is even MORE important.

And, static gremlins abound in dry environs. I've seen huge work stoppages result from static discharge in winter months--people claiming that electrical equipment hadn't been properly de-energized, locked out, and tagged out. Only to find all was proper, and the most likely cause was static discharge from polyester clothing developing a charge because of rubbing.

Good to hear from you again! Hope all is well!!!

By Curt Wuollet on 12 February, 2018 - 11:23 pm

Today I was commissioning a raspberry pi for a signage project. Once I put it in its aluminum case, all I had to do was stand up and the field would shut it down. Attach a ground wire, and it was bulletproof. The thousands of wooden doors absorb what humidity there is, so the RH can go below what common hygrometers will measure.