ETS-Lindgren HI-3603 VLF Survey Meter - Manual (Page 32)

HI-3603 VDT/VLF Survey Meter
© ETS-Lindgren, August, 2005
Revision E, Part # H-600042
32
Measurements of the magnetic field strength are considerably
less difficult since the presence of the human body does not
perturb the magnetic field. In this case, the instrument is
generally held so that the sensor paddle is in an orientation that
yields the maximum reading on the LCD screen. For most VDT's
this will be in a horizontal position with the paddle facing upward
with the center of the paddle located at a distance of 30 cm from
the front of the VDT screen. Because the body does not
influence the magnetic field, the user may, if desired, directly
hold the HI-3603 for these measurements.
Figure 9: Using the non-conductive holder with the HI-3603
to perform a VDT survey.
Care should be taken in positioning the sensor for both electric
and magnetic field measurements because the spatial variation
in both fields near the VDT surface is very rapid. To illustrate
how rapidly these fields vary with distance from the VDT, Figure
10 is a plot of data collected with the HI-3603 near a commonly
used monochrome monitor. The distances shown are between
the screen surface and the surface of the sensor paddle for the
electric field values and between the screen surface and the
center of the sensor paddle for magnetic field values. Because of
the finite size of the sensing loop, magnetic field measurements
will be representative of averages of the field strength over the