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Re: [TCML] Strange Voltmeter Behavior



Steve,

Its and electrostatic phenomenon. I've seen this occur with some panel meters from electrostatic surface charges that become trapped on the clear plastic top surface of the meter. A significant patch of trapped charge attract the meter needle, causing a positional offset. Surface charges on many polymers, once created - possibly during the last time you wiped or dusted the surface - can take days, or even months, to dissipate.

When you contacted the charged surface, you changed the distribution and polarity of localized surface charge patches, but did not eliminate them. You might try wiping the meter surface with a cloth dampened with a bit of soapy water or apply a bit of anti-static fluid to increase surface conductivity.

Bert

Steve White wrote:
In the control cabinet for my SGTC I have a Simpson 0 - 300 volts AC Wide-View iron vane voltmeter measuring the voltage from the wall. I briefly powered up the cabinet for a few seconds to check some things and then switched it off. Then, with all power off, I placed my finger over the indicator pointer of the voltmeter and its movement tracked my finger movement through the clear plastic cover! After this strange behavior, the pointer settled at a position substantially above the zero voltage point. It settled at about 30 volts with no power applied. I noticed that as time went by, the pointer gradually settled back to its true zero voltage point. This took about 10 minutes. I have PFC capacitors but I had them switched out at the time. The only other energy storage components that I can think of are the capacitors in the EMI line filter bricks. I don't think it could be static electricity because I tried discharging my body and the pointer still followed my finger. None of
   the other voltmeters and ammeters in the control cabinet display this strange behavior. Does anyone know what is going on here?

Steve
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