MadSci Network: Computer Science

Re: Will a Faraday Cage place over a compuer monitor make it ESD safe?

Date: Thu Jan 30 07:10:12 2003
Posted By: Dietmar Hildebrand, Post-doc/Fellow, Radiation Biophysics,
Area of science: Computer Science
ID: 1043441474.Cs

ESD effects on computers are rarely caused by monitors. Since CRTs work by shooting electrons onto a phosphor screen they are actually natural van de Graf generators. So every CRT designer will make sure that the CRT discharges itself continuosly and the electrical safety regulations enforce proper grounding (otherwise the product would not get the desired UL label).

The common cause for discharge problems with computers is discharge through the human user. Our fingers on the keyboard are the most common problem. Discharges coming in from the keyboard can for a split millisecond reverse the polarity at signal and power inputs of ICs. Their most common reaction is: funny output... which typically causes a system to crash or even hang. To kill the ICs the discharge must have a substantial integral value.

In the old days of computing, where ICs easily died from discharge, people simply attached wire chains to their ankles, which made sure that the body was grounded against the floor. And service personnel touching sensitive parts used wrist bands, which were connected to a good ground contact.

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