Wednesday, November 16, 2005

Recently I complained about a low charging bag. The manufacturer came to me and he wanted to prove that the bags are suitable. He used a charged plate monitor. He charged it to 1000V. He connectted his wist strap to EPA ground, than he touched the plate with the bag. He measured the time taken for the voltage to decay to 100V. I think it's not an adequate method.

Whether on not it is an adequate method it is not a standard test method used in 61340-5-1 for demonstrating compliance of packaging. Actually it works by electrical conductivity and so is not even a test of "low charging" but is a sort of "charge decay" test of conduction properties. In the case of "low charging" there is no test method in 61340-5-1, neither is there any pass/fail criteria. But I would not use "low charging" bags for protection of ESDS, I would only use them to package documents or non-ESDS components to prevent them causing electrostatic fields.

For use to protect ESDS within the EPA under the 61340-5-1 standard the bags must be low charging AND either dissipative or conductive. They should therefore pass the criteria using a surface resistance measurement. If the bag does not pass this then it is not compliant with 61340-5-1.

To protect ESDS outside the EPA the total packaging solution (which could have many packaging types e.g. conductive box and dissipative foam) should also have shielding properties.

4 comments:

Pamela said...

Hello. I recently purchased a new microsuede couch. For some reason it is full of static electricity and I keep getting painful shocks. Initially, I was keeping my powerbook on the couch, but I kept shocking myself (and the powerbook) each time I picked it up. Did a google search to see how much damage I may have caused the computer and found your site. Extremely informative. Now if only I could figure out how to rid my couch of this static once and for all. In the meantime, I no longer put the computer on the couch, and discharge on another object before I pick it up. Thanks again.

Static Doctor said...

Have you read my on-line article on static shocks and how to avoid them?

The problem may be due to the material of the couch cover - maybe you also have dry air conditions that could make the problem worse. You may be able to get an anti-static fabric spray - make sure it cannot damage the materials before you use it. Otherwise cleaning the fabric with a conditioner might help.

Andrew Defries (Cutler Lab) said...

Unrelated question.

I work in a lab, and deal with powdered chemicals often. The chemicals are housed in polypropylene plastic tubes and have a considerable amount of static in them.

I would like to reduce the static of these chemicals to assure more precise handling. Could you suggest a solution?

I've been looking into ionizing air devices. What do you think of them?

Thanks

Static Doctor said...

An ioniser might do the trick - depending on the situation, it's hard to say without seeing it for myself. An ioniser will not be able to neutralise static inside the tube or in the powder mass. Only external surfaces will be neutralised.

As soon as the powder moves, it will tend to charge itself up again. It can be a difficult problem.