ETS-Lindgren HI-3603 VLF Survey Meter - Manual (Page 40)

HI-3603 VDT/VLF Survey Meter
© ETS-Lindgren, August, 2005
Revision E, Part # H-600042
40
The measurement procedure consists of using the oscilloscope
to determine (1) the peak-to-peak magnitude of the magnetic
field strength and (2) the time for the magnetic field to go through
its most rapid transition (flyback time). Figure 13 is an
oscilloscope photograph showing an actual measured waveform
of the magnetic field near the screen of an operating VDT. The
observed waveform may be inverted from that shown in Figure
13 depending on the orientation of the HI-3603 paddle sensor
relative to the field. This has no impact on the assessment and
the part of the waveform exhibiting the most rapid change with
time should be carefully inspected to determine the transition
time. In Figure 13 the time base of the oscilloscope was set to 20
microseconds per horizontal division and the vertical sensitivity
to 10 mV per division. In this case the flyback time (time during
which the electron beam is repositioned to the left side of the
screen) is approximately 8 microseconds. The measured peak-
to-peak magnetic field strength is obtained from the waveform as
approximately 370 mA/m. The time rate of change of the
magnetic field strength is then obtained by dividing the peak-to-
peak field strength by the transition time; in the example case a
value of approximately 4.6x107 (mA/m)/sec or 58 mT/sec peak-
to-peak is obtained.