Video Display Terminal
Electric and Magnetic Fields

Numerous surveys of electric and magnetic fields associated with video display terminals (VDTs) have been accomplished by Richard Tell Associates. These devices produce strong surface electric fields due to the high voltage lead emerging from the fly-back transformer. Because of the various arrangements of this lead, the large red cable in the photo to the right, VDT electric fields are not as easily predicted from one VDT to another. Magnetic fields, however, produced by the fly-back transformer and the deflection yoke located at the rear of the CRT neck (copper colored wire seen in this photo) are generally well characterized by a vertically polarized component due to the horizontal scan on the CRT (typically in the 15 kHz to 65 kHz range) and a horizontal component due to the vertical scan on the CRT (typically in the 45 to 75 Hz range).


Projects carried out under contract to the National Institute for Occupational Safety and Health, for example, beyond the usual measurement of electric and magnetic field strengths, have included measurement of currents flowing in the operator induced by electric fields. and investigation of the time-domain waveforms of magnetic fields.





The time-derivative of the VDT's sawtooth like magnetic field waveform is related to the magnitude of the induced peripherial eddy currents in the body of the operator.