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| off-zero analog meter because of static charge on its face... |
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| wetbox:
Today I received an almost mint HP 6827A with both front panel indicators way off zero, and very responsive to the position of my fingers! After 'fixing' one of the two meters by breathing on it, I made a short clip of the other - let's see if I can attach it as a zip file. The clear plastic can easily be recharged to reintroduce the off-zero by rapidly wiping the meter face with a finger, and the same works for several of my other instruments. I guess it is to be expected on a relatively dry winter day, but I never thought of waving my finger by an analogue meter to verify that static charge on its face is not biasing the reading... VID_20210208_163949_s.zip |
| TimFox:
Back in the day, I often saw that effect on sensitive d’Arsonval meters (say, 50 uA and below full-scale) during the winter with very low indoor humidity. When necessary, I would lightly rub the clear plastic surface with a moist tissue paper before making the measurement. |
| Kleinstein:
A have an older (1980s) russian analog multimeter, that was essentially non working for some 2 year due to static charge. The needle nearly stuck at a point near 70% FS, causing extreme nonlinearity (could still use 0-20% :-BROKE). Waiting did not solve the problem - I finally opend it and removed the charge from the inside surface with some water. It now works again. It does not take a dry winter day - just some wipe with wool. |
| Tomorokoshi:
A long time ago I found someone's topic regarding restoration of similar HP equipment with meters like that. His solution was to gently wipe the surface with clean pencil soft lead shavings. This left a static dissipative layer that was good enough to drain any static buildup on the surface. It was thin enough to be invisible. Unfortunately I can't find that topic any more. |
| coppice:
I used to own a large TMK 100k ohm per volt (10uA full scale) analogue multimeter which could be quite susceptible to static charges altering the reading in very dry conditions. When it takes so little current to move the pointer, its not too surprising other spurious forces can influence it too. It was a lovely instrument for its time, despite this effect. |
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