Strange analog meter movement problem

[Sam Goldwasser]

Now here's one you don't see everyday.

I have a taut band (I believe) D'Arsonval meter movement with a
plastic faceplate that seems to have areas of permanently static charge.
So, the needle gets stuck or gets pulled or pushed toward or away from
certain positions. I've removed the faceplate and it then works normally.
Moving the faceplate near the needle results in the needle changing
position. I've tried the usual approaches to getting rid of static but
it always comes back.

Assuming anyone has seen this before, is there any solution other than
replacing the faceplate? Is there such a thing as "degaussing" for
electrostatic charges? Destatic-ing?

I'd rather not have to fabricate a replacement.

Thanks.

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[Michael Black]

Now here's one you don't see everyday.

I have a taut band (I believe) D'Arsonval meter movement with a
plastic faceplate that seems to have areas of permanently static charge.
So, the needle gets stuck or gets pulled or pushed toward or away from
certain positions. I've removed the faceplate and it then works normally.
Moving the faceplate near the needle results in the needle changing
position. I've tried the usual approaches to getting rid of static but
it always comes back.

Assuming anyone has seen this before, is there any solution other than
replacing the faceplate? Is there such a thing as "degaussing" for
electrostatic charges? Destatic-ing?

I'd rather not have to fabricate a replacement.

Thanks.

Your post makes me want to say "rub a small amount of liquid dish
detergent on the inside of the meter face".

The problem is, I can't remember if that's a solution for the problem,
or I am remembering a solution to some other problem.

Michael

 

[Dbowey]

Michael posted:
<< Your post makes me want to say "rub a small amount of liquid dish
detergent on the inside of the meter face".

The problem is, I can't remember if that's a solution for the problem,
or I am remembering a solution to some other problem. >>

That is the correct answer. I've used it many times.

Don

 

[Daniel Rudy]

And somewhere around the time of 02/19/2004 19:42, the world stopped and
listened as Dbowey contributed the following to humanity:

Michael posted:
<< Your post makes me want to say "rub a small amount of liquid dish
detergent on the inside of the meter face".

The problem is, I can't remember if that's a solution for the problem,
or I am remembering a solution to some other problem. >>

That is the correct answer. I've used it many times.

Don

Why not use an anti-static spray on it? They don't cost much, and
because the residue is slightly conductive (depending on which one you
use), the metal case of the meter (If it has a metal case) would serve
as an electrical ground. But, then again, I don't know if the spray
would harm the plastic either.

 

[Russ Verdon]

There was a post on an electronics group the other day about this same
problem. A guy on a boat was having trouble with an in strument meter.
An amateur radio respondee advised that he sprayed the plastic with fabric
conditioner IIRC as required.

Russell

 

[Sam Goldwasser]

Your post makes me want to say "rub a small amount of liquid dish
detergent on the inside of the meter face".

The problem is, I can't remember if that's a solution for the problem,
or I am remembering a solution to some other problem.

Thanks. Yes, I tried cleaning the inside but that didn't help.

I may try the applying a HV AC field across aluminum foil plates
to see if I can depolarize the plastic on the assumption that it
somehow acquired some internal polarization from an "event".

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[Hubert Littau]

And somewhere around the time of 02/19/2004 19:42, the world stopped and
listened as Dbowey contributed the following to humanity:


Why not use an anti-static spray on it? They don't cost much, and
because the residue is slightly conductive (depending on which one you
use), the metal case of the meter (If it has a metal case) would serve
as an electrical ground. But, then again, I don't know if the spray
would harm the plastic either.

Just a shot in the dark here, but I seem to remember insuring the
conductivity across a clear material by taking a cotton ball and using
it to rub dry graphite into the material. Works great for making
replacement films for electrostatic speakers too. You may also want to
make a conductive path from the lens to the system ground as well.
Foil tape should work for this.

 

[H. Dziardziel]

Now here's one you don't see everyday.

I have a taut band (I believe) D'Arsonval meter movement with a
plastic faceplate that seems to have areas of permanently static charge.
So, the needle gets stuck or gets pulled or pushed toward or away from
certain positions.

Not sure if I read that right:? Pulled and pushed as the needle
moves? That would seem to imply reversing charges (polarity
changes) as the needle moves under the faceplate

snip

 

[Sam Goldwasser]

Just a shot in the dark here, but I seem to remember insuring the
conductivity across a clear material by taking a cotton ball and using
it to rub dry graphite into the material. Works great for making
replacement films for electrostatic speakers too. You may also want to
make a conductive path from the lens to the system ground as well.
Foil tape should work for this.

You do have to be able to see through this so a visible coatin of
graphite powder or aluminum strips isn't exactly a viable solution.

I finally fixed it by rubbing with a clothes dryer anti-cling sheet but
had to do both inside and outside.

Thanks for all the replies.

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
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[Sam Goldwasser]

Not sure if I read that right:? Pulled and pushed as the needle
moves? That would seem to imply reversing charges (polarity
changes) as the needle moves under the faceplate

Yes. Up around 2/3 scale it might tend to get stuck while it would tend
to want to avoid around 0.

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
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[Ken G.]

Get a digital meter .

 

[Sam Goldwasser]

Get a digital meter .

No. There are times when an analog meter is far superior as when
following a trend. Anyhow, this is for an existing instrument
where that isn't an option.

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
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[Jim Adney]

Assuming anyone has seen this before, is there any solution other than
replacing the faceplate? Is there such a thing as "degaussing" for
electrostatic charges? Destatic-ing?

I'm just guessing here, so be gentle with me. How about rubbing it
VERY lightly with a (possibly warm) anti-static dryer sheet?

-

 

[Sam Goldwasser]

I'm just guessing here, so be gentle with me. How about rubbing it
VERY lightly with a (possibly warm) anti-static dryer sheet?

Yes, that finally was the solution. Maybe more determined cleaning with
dishwashing liquid would also have suceeded. The dryer sheets worked
the first time though I did have to do both inside and outside.

Thanks.

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
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[H. Dziardziel]

Yes. Up around 2/3 scale it might tend to get stuck while it would tend
to want to avoid around 0.

Thanks. What do you think about this? That area corresponds to
the needle's most active area. It may have, over time, swept
that area relatively free from outgassing by the scale paint
graduations? Or there are very dense etc., markings at the ends.

Oh well, it's raining today....
..

 

[Sam Goldwasser]

Thanks. What do you think about this? That area corresponds to
the needle's most active area. It may have, over time, swept
that area relatively free from outgassing by the scale paint
graduations? Or there are very dense etc., markings at the ends.

Too much in depth analysis can be a bad thing sometimes.

Oh well, it's raining today....

Probably the correct explanation!

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
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[H. Dziardziel]

snip

Too much in depth analysis can be a bad thing sometimes.

Then I 'll have to start drinking again!

Probably the correct explanation!

Timely that too, thanks again Sam.