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Re: [TCML] Strange Voltmeter Behavior


I think I got more responses to this question than I have ever received for any other question. Thanks for the replies. So now I know it is just static buildup. For tesla coil use I actually prefer the analog meters over the digital ones. I think they are more rugged and can be read more quickly than a digital meter under tesla coil operating conditions. I also think they look more impressive. It gives the control cabinet more of that old-school mad scientist look.

I have 4 Simpson meters mounted on a steel panel. Three are moving iron vane and 1 is rectifier-type. I was concerned about the steel mounting and that they are also within 6 inches of a large contactor. I checked them against my Fluke DVM and they match to within a few percent so the steel and contactor doesn't seem to be affecting them.


----- Original Message -----
From: "Terry" <terry@xxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Thursday, May 10, 2018 11:35:16 AM
Subject: Re: [TCML] Strange Voltmeter Behavior

It is static charge on the meter face plastic. Seen this before as I 
worked in a calibration lab at Lockheed for 38 years.  We always had a 
spray bottle that cleaned meters plastic faces and also removed the 
static charge. We also had kits to replace the meter movements and 
techniques to balance the meter reading so the needle was the same 
reading with the meter placed horizontal on its back versus vertical 
standing up. Had a lot of experience with Simpson and other analog 
meters decades ago. Simpson made some good meters and this was before 
digital readout devices were widely used, portable, or affordable.
Note when mounting meters in metal panels in some cases the type of 
metal can affect the meter accuracy. Best to calibrate or check the 
meter accuracy while mounting in the panel if concerned.
If you get any iron fillings  in the meter movement core that with give 
erroneous reading also. But the key to the static problem as I see it is 
that you say the meter tracked your fingers. Even wet saliva smeared on 
the meter plastic face, although not preferred, should show a change and 
help this problem .
Looked with Google search and there are anti-static spray products but 
did not find the one we used to use. Sorry I no longer recall the name 
of the product.
Terry Leonard

On 5/9/2018 9:17 PM, 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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