ETS-Lindgren HI-3604 ELF Survey Meter - Manual (Page 34)

Page -- 26 HI-3604 Manual
help align the sensor). In this orientation, the sensor loop is
aligned so that the maximum number of magnetic field flux lines
pass through the loop aperture. While performing magnetic field
measurements, the HI-3604 may be held by the operator. The
non-magnetic nature of the human body does not perturb the
magnetic field nor interfere with the operation of the sensor.
Waveform Measurements
A useful feature of the HI-3604 is the ability to display
waveform information about electric or magnetic fields being
sensed. The waveform display output is a 1/8 inch phone jack
located on the bottom of the instrument case. Using this output,
the waveforms of the incident fields maybe monitored by
connection to an oscilloscope.
Figure 5-3 is an oscilloscope photograph of the magnetic field
associated with a common incandescent light bulb. The field
waveform is seen to be essentially a pure 60-Hz sinusoid. Figure
5-4 is a picture of the waveform of the same light bulb
magnetic field except that a light dimmer has been introduced
to the power supply to the light bulb. In this case, the dimmer
has been adjusted to approximately half brilliance and the
chopping action of the dimmer is clearly shown. Through a
chopping of the waveform, less power is delivered to the bulb
resulting in a lower light level. Figure 5-5 represents the
waveform of the current supplied by the light dimmer.
Figure 5-6 illustrates yet another application of the HI- 3604 in
the measurement of the magnetic field waveform caused by the
vertical deflection circuits in a typical video display terminal
(VDT). The images displayed on the screen of a VDT consist of
many horizontal sweeps of an electron beam across the screen
to trace out the intended image; when the electron beam
reaches the bottom of the screen, it is returned rapidly to the
top of the screen from where it again repeats its scan across
and down the screen. This vertical refresh, as it is called, gives
rise to a triangular shaped waveform which is related to the
time during which the beam is being scanned vertically. The