Interference from 60 Hz Electric and Magnetic Fields on Personal Computers

This paper discusses some 60 Hz electric and magnetic field interference tests on personal computers. Test results are interpreted for long-term and short-term use of personal computers in 60 Hz electric and magnetic field environments. The effects of 60 Hz electric field interference appeared as an injection of spurious data when a spark train occurred on a powjer supply circuit and the potential of the computer operator's body was raised above 15 volts with respect to the keyboard. The effect of 60 Hz magnetic field interference were noticed as oscillating distortions of the images on the monitor. Oscillating distortions caused by typical power system magnetic field levels were effectively reduced with a special Mu metal box, whichi encloses the computer monitor on five sides. The sixth side was left open for viewing the monitor screen. The computer monitor raster vertical scan frequency was determined to be a critical parameter in the human sensitivity to the magnetic field interference. The larger the difference between the raster vertical scan frequency and the frequency of the interfering magnetic field, the faster the interference scrolling period, and thus more noticeable the distortion.