ETS-Lindgren HI-3603 VLF Survey Meter User Manual
Page 33
HI-3603 VDT/VLF Survey Meter
© ETS-Lindgren, August, 2005
Revision E, Part #H-600042
33
area of the sensing loop. As the distance between the probe and
the screen is decreased, greater error will exist in the indicated
value of magnetic field strength. This spatial averaging error
diminishes rapidly with distance from the VDT since the field
rapidly becomes more uniform.
Figure 10: Typical VDT RMS electric and magnetic field
strength variation with distance from the screen.
Because the electric and magnetic field gradients are so great
near the VDT, significant error may occur if extra care is not
exercised when attempting repeated measurements at a specific
location. This is apparent when holding the instrument without a
tripod very near the screen and attempting to obtain a constant
reading of field strength. To enhance the repeatability of field
measurements near VDT's, a tripod or stand that provides
electrical isolation for the meter should be used. A stand
fabricated from a non-conductive material is preferable to avoid
the same problem that occurs when the user directly holds the
instrument and measures electric fields.