Static charge on a piece of plastic

To discharge static charges you must ground the item.

Proper use of this sensitive equipment would probably require a properly grounded static mat and strap.

Hold the lid and wear a grounded static strap.

If this is not available, as most electronic equipment is grounded, attach the lid to the frame of what you are testing. A simple wire with alligator clips on both ends will do. If this is not available, hold the lid and lean against the cabinet with the same arm.

A positively charged piece of plastic will lose it's charge naturally over time, due to ions in the air. You can speed up the process considerably (as fast as one second) by using an antistatic ionized air blower made just for such things. Using the air ionizer will also keep the static from ever building up in the first place.

If this is something you're manufacturing, you should consider replacing the plastic with a more conductive plastic, such as that used in industry for handling microcircuits.

If you're referring to an analogue meter movement, you do say the effect on a needle.

Then all analogue meters are made with either a clear metal coating on the glass which is connected to ground, or with the cheaper ones the plastic contains a slightly conducting material to allow the static to leak quickly to earth.

A simple experiment is to remove the glass front from an analogue meter movement and replace it with a piece of transparent plastic, you will see that when you wipe a finger across the plastic the needle will show a displacement which can last for several hours. That's why conductive glass / plastic is always used.

John.

If this is a device used only occasionally, just spray (a very light mist of water) or wipe it with a damp cloth - The water will be sufficiently conductive to carry away the charge (assuming the device has a metal case, otherwise you have to ground the water film somehow,possibly by touching it).

Other posts have suggested more permanent solutions...

What about those Piezo static guns we had for LPs?

On second thoughts you did say 'sensitive', but they hardly worked on Lps anyway!

Humidity is the best answer.

I think that just wiping down with water with a little dishwashing detergent in it does the trick. That used to be recommended for plastic lense covered electrical gages where static charge on the lense could upset the reading. The deterent residue will work for months bleeding off static charge.