Re: ELF Effects on VDUs

[Donald Haes <HAES%MITVMA.bitnet@vmd.cso.uiuc.edu>]

Gordon is right. The refresh (50-70Hz) rate can affect the operation
of a VDU (VDT). Initial data suggests the 5 mG threshold, but I have
seen fields as low as 2 mG causing a "jitter" or "shaking" (for more
synonyms, refer to "AIRPLANE II"). This is a real problem, especially
if there is sufficient resolution in the screen to perceive the
movement. I have also noticed "blooming" (color changes) in screens
where the static flux density is a low as 1.5 G: due to inherent
magnetism in the structural steel. Did you measure using a broadband
probe? Were you measuring harmonics with the 50Hz? We have had limited
success with measuring 60+/- 5Hz fields, and picking the lowest area
for the VDT. Better results are obtained by placing the best choice
for the "meter"; the VDT itself, on a tea-cart, and moving it around the
area while energized; then parking it where it works best. I know it seems
archaic, but after almost 100 investigations, it works best. Good luck!