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From: Andrew VK3BFA on 27 Apr 2010 10:04
On Mar 17, 11:57 am, "Dave M" <dgminala4...(a)mediacombb.net> wrote:
> Jeff Liebermann wrote:
> > On Thu, 25 Feb 2010 07:32:28 -0800 (PST), klem kedidelhopper
> > <captainvideo462...(a)gmail.com> wrote:
>
> >> After setting zero I moved my finger over the meter face first thing
> >> in the morning and the needle moved up scale about 10 percent. I let
> >> it sit on the bench for about 24 hours without touching it. When I
> >> looked at it again it was back to zero. So the trick is to set it,
> >> leave it for a day let it discharge, and then tweak it again. Clumsy
> >> procedure but it works. Glad this is my own equipment and not a
> >> customer repair job....Lenny
>
> > Nice workaround.  So it is static.  Is this NORMAL for a small panel
> > meter?  We don't have much of a static problem on the left coast, so I
> > don't see much of that.  I waved my hand around various small panel
> > meters around the shop.  No deflection.
>
> The easiest and best solution is to eliminate the static charge by rubbing
> the meter face with a clothes dryer anti-cling sheet. Alternatively, buy a
> bottle of anti-cling spray and give the meter a ligh misting.
> That will dissipate the static charge and you can handle the meter as you
> wish without upsetting the zero setting.
>
> --
> David
> dgminala at mediacombb dot net

This all sounds terribly bizarre - Its a moving coil meter, it might
go "whack" on getting a static charge, but a steady reading? - must be
an INCREDIBLY sensitive meter movement- femtoamps? - have a look at
the output of the op amp, preferably with an analogue meter - (as
suggested) (no signal, 0 output) and the bias resistors around it.
Especially the high value (>100k ones) (any Tantalum capacitors,
replace them)
(sorry Dave - a view from the trenches)

Andrew VK3BFA.

PS - its axiomatic that the thing causing the fault is in the least
accessible section of the cct. A variation of Murphys Law.
From: greenpjs on 27 Apr 2010 15:52
On Tue, 27 Apr 2010 07:04:53 -0700 (PDT), Andrew VK3BFA
<VK3BFA(a)wia.org.au> wrote:

>On Mar 17, 11:57�am, "Dave M" <dgminala4...(a)mediacombb.net> wrote:
>> Jeff Liebermann wrote:
>> > On Thu, 25 Feb 2010 07:32:28 -0800 (PST), klem kedidelhopper
>> > <captainvideo462...(a)gmail.com> wrote:
>>
>> >> After setting zero I moved my finger over the meter face first thing
>> >> in the morning and the needle moved up scale about 10 percent. I let
>> >> it sit on the bench for about 24 hours without touching it. When I
>> >> looked at it again it was back to zero. So the trick is to set it,
>> >> leave it for a day let it discharge, and then tweak it again. Clumsy
>> >> procedure but it works. Glad this is my own equipment and not a
>> >> customer repair job....Lenny
>>
>> > Nice workaround. �So it is static. �Is this NORMAL for a small panel
>> > meter? �We don't have much of a static problem on the left coast, so I
>> > don't see much of that. �I waved my hand around various small panel
>> > meters around the shop. �No deflection.
>>
>> The easiest and best solution is to eliminate the static charge by rubbing
>> the meter face with a clothes dryer anti-cling sheet. Alternatively, buy a
>> bottle of anti-cling spray and give the meter a ligh misting.
>> That will dissipate the static charge and you can handle the meter as you
>> wish without upsetting the zero setting.
>>
>> --
>> David
>> dgminala at mediacombb dot net
>
>This all sounds terribly bizarre - Its a moving coil meter, it might
>go "whack" on getting a static charge, but a steady reading?
It is NOT current flow from a static discharge that creates the
reading. It is a static (as in unchanging) charge on the case
attracting or repelling some other part of the movement.



- must be
>an INCREDIBLY sensitive meter movement- femtoamps? - have a look at
>the output of the op amp, preferably with an analogue meter - (as
>suggested) (no signal, 0 output) and the bias resistors around it.
>Especially the high value (>100k ones) (any Tantalum capacitors,
>replace them)
>(sorry Dave - a view from the trenches)
>
>Andrew VK3BFA.
>
>PS - its axiomatic that the thing causing the fault is in the least
>accessible section of the cct. A variation of Murphys Law.
From: Paul Hovnanian P.E. on 28 Apr 2010 13:32
Andrew VK3BFA wrote:

> On Mar 17, 11:57 am, "Dave M" <dgminala4...(a)mediacombb.net> wrote:
>> Jeff Liebermann wrote:
>> > On Thu, 25 Feb 2010 07:32:28 -0800 (PST), klem kedidelhopper
>> > <captainvideo462...(a)gmail.com> wrote:
>>
>> >> After setting zero I moved my finger over the meter face first thing
>> >> in the morning and the needle moved up scale about 10 percent. I let
>> >> it sit on the bench for about 24 hours without touching it. When I
>> >> looked at it again it was back to zero. So the trick is to set it,
>> >> leave it for a day let it discharge, and then tweak it again. Clumsy
>> >> procedure but it works. Glad this is my own equipment and not a
>> >> customer repair job....Lenny
>>
>> > Nice workaround.  So it is static.  Is this NORMAL for a small panel
>> > meter?  We don't have much of a static problem on the left coast, so I
>> > don't see much of that.  I waved my hand around various small panel
>> > meters around the shop.  No deflection.
>>
>> The easiest and best solution is to eliminate the static charge by
>> rubbing the meter face with a clothes dryer anti-cling sheet.
>> Alternatively, buy a bottle of anti-cling spray and give the meter a ligh
>> misting. That will dissipate the static charge and you can handle the
>> meter as you wish without upsetting the zero setting.
>>
>> --
>> David
>> dgminala at mediacombb dot net
>
> This all sounds terribly bizarre - Its a moving coil meter, it might
> go "whack" on getting a static charge, but a steady reading? - must be
> an INCREDIBLY sensitive meter movement- femtoamps? - have a look at
> the output of the op amp, preferably with an analogue meter - (as
> suggested) (no signal, 0 output) and the bias resistors around it.
> Especially the high value (>100k ones) (any Tantalum capacitors,
> replace them)
> (sorry Dave - a view from the trenches)
>
> Andrew VK3BFA.
>
> PS - its axiomatic that the thing causing the fault is in the least
> accessible section of the cct. A variation of Murphys Law.

I think the static charge thing refers to a force produced directly by a
static charge on the plastic meter face acting against the needle, not a
current flowing through the coil.

--
Paul Hovnanian paul(a)hovnanian.com
----------------------------------------------------------------------
Have gnu, will travel.
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