Re: VDT Displays Distorted by H Fields

[Tad Blanchard <Tad.M.Blanchard.1@gsfc.nasa.gov>]

We recently visited a remodeled office where personnel were concerned about
magnetic fields because their VDT output colors were distorted.  I
investigated and found that the units were operating fine before the
renovation.  

I determined that the cause of the distortions were the new "metal"
cabinets on which they had placed the VDTs.  When we lifted the units off
of the metal shelving, the distortion disappeared.  Evidently the
transformers in the VDTs were causing the problem.



 

At 12:41 PM 12/20/96 -0600, you wrote:
>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
>
>
**************************** /^\   /^\ *********************************
Tad  Blanchard              /__ \ /___\    NASA-Goddard Space Flt Ctr 
Nat'l Health Svc, Inc            O             Greenbelt, Maryland     
Sr Health Physics Tech          / \            Phone: 301-286-9157     
Assistant RSO                  /___\           Fax:   301-286-1618       
                  Tad.M.Blanchard.1@GSFC.NASA.gov                   
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