Accounting for stochastic quantities in calculating interference voltages

Interference voltages caused by electromagnetic emissions and induced into cables and equipment may impair the correct operation of electronic systems or, depending on the source strength, even destroy them. This is of particular concern if safety systems are affected. A technical countermeasure is a grounded shield. This is normally designed using single (point) values for the input quantities (source strength, shield thickness etc.) of the corresponding design calculation. Possible design errors caused by ignoring the stochastic nature of many of these quantities are counteracted by safety factors. Such a procedure does, however, not permit safety margins to be quantified. By treating stochastic quantities as random variables and propagating their variation through the calculations it is shown that the failure probability of a specific design may be calculated. This enables one to judge whether the degree of protection is sufficient or not. It thus provides a basis for avoiding under or overdesign. (C) 2000 Elsevier Science Ltd. All rights reserved.