VDT Displays Distorted by H Fields

[Erick Lindstrom <avrel@gemini.oscs.montana.edu>]

Happy Holidays Radsafers:

Montana State University just finished constructing a new Engineering and
Physical Sciences Building (EPS).  Our Physics Department recently occupied
the second floor of that building.  A number of the faculty and graduate
students then began complaining about color shifts and distortion in their
VDT displays.  We have been able to subsequently verify that many of the
girders used in the building have somehow become magnetized.  The DC H
fields we are seeing are in the range of 0.4 - 2.0 mTesla (4 - 20 gauss)
using a Holaday HI-3550 magnetic field monitor (we also verified that there
were no ELF fields contributing to the problem).  We've additionally
eliminated the possibility of interference from the large superconducting
magnets the Department uses (although you should have seen the effect that
the large magnets had on the Hall sensors used in the building's elevators!).

Do any of you folks happen to know of any studies that have focused on
variable H field (DC) intensities and their effects on specific models of
VDTs (e.g., the Sonys, the Digitals, the NECs, MACs etc.)?  My aim here is
to compare that data (if it exists) with what we are seeing in the EPS
building.  Ironically, I've got beaucoup info regarding VDT VLF emissions,
but nothing that addresses (in detail) how discrete H fields can perturb
their visual output!

All responses will be sincerely appreciated!

-Erick Lindstrom


 Erick Lindstrom
 Radiation Safety Officer
 Montana State University
 309 Montana Hall
 Bozeman, MT  59717-2440
 Phone: (406) 994-2108
 Fax:	(406) 994-4792
 avrel@gemini.oscs.montana.edu