William (Bill) L. Mostia, Jr., P.E., Amoco Corp.

Understanding and preventing radio frequency interference – 1998-09-01

Radio-based devices such as walkie-talkies and pagers have been used in our plants for many years but in recent years there has been an increased number of radio frequency sources both inside and outside our facilities. This combined with the greater clock speed of our microprocessor-based systems and increased use of digital communication systems complicates the electromagnetic environment in our facilities. Our instrumentation systems must be able to function in the presence of high-frequency interference which is commonly referred to as radio frequency interference (RFI). It is also sometimes referred to as electromagnetic interference (EMI), though this is somewhat of a misnomer as EMI covers a wider range of frequencies. RFI can be defined as objectionable high-frequency electromagnetic radiation where the source is further away than the radiation's wavelength (l) divided by 2p, i.e.

Electrical noise—what a racket

Every electrical circuit has noise in it. Noise becomes undesirable when the signal-to-noise ratio becomes low enough to adversely effect the operation of the electrical circuit.Electrical or electromechanical devices that cause fast or large changes in voltage or current are common sources of noise.