ETS-Lindgren HI-3627 ELF Magnetic Field Meter - Manual (Page 23)

HI-3627 Manual Page --15
may be taken relative to the sides, the top and the back of the
VDT to explore the distribution of the fields about the VDT.
The second method involves a measurement at the position of
the VDT operator to assess the flux density to which the
operator is actually exposed while sitting at the VDT. Because
different individuals will sit at different locations and have
different postures, the operator exposure measurement may be
more a function of the operator than of the specific VDT. A
reasonable approach for the operator exposure measurement is
to position the sensor at a point corresponding to where the
center of the body would be located during operation of the
VDT.
It is important to note that the magnetic fields decrease very
rapidly with increasing distance from the screen. Because of this
characteristic, it is important to insure that the position of the
sensor is precisely known. Attempts to repeat the measurement
results will be hampered by unnecessary variability if the sensor
is not replaced at the same exact position. Spacing
measurements should be made from the VDT surface to the
center of the sensor.
The Model HI-3627 contains circuitry to extend the lower
frequency response down to 5 Hz in accordance with
recommendations used for VDT measurements according to the
guidelines issued in Sweden for extremely-low-frequency (ELF)
magnetic fields produced by video display terminals (VDTs). The
user is referred to the Swedish specifications for measurement
(2) for application details.
Residential Measurement Surveys
Magnetic fields found in home environments are highly variable,
depending on location within the home. This variability is
strongly related to the distribution of the wiring in the home, the
location of electrical appliances and, sometimes, the location of
plumbing lines or other metallic structures within the ground
which may form low resistance paths for electrical ground