ETS-Lindgren HI-3603 VLF Survey Meter - Manual (Page 14)

HI-3603 VDT/VLF Survey Meter
© ETS-Lindgren, August, 2005
Revision E, Part # H-600042
14
mode of the HI-3603, the frequency response for the principal
VDT fly-back circuit emissions will be flat within ± 1 db or better.
Subjecting the instrument to electric or magnetic fields with
different waveforms but having the same RMS magnitude can
assess the effectiveness of the true RMS detector in the HI-
3603. Representative data from such a test are given below
where the instrument response to a sinusoidal waveform is
compared to its response to a saw-tooth waveform similar to that
found in VDT's (a rise time equal to 9 times the duration of the
fall time of the signal) but having the same RMS magnitude.
Frequency Sine wave Saw-tooth
wave Difference
10 kHz 253 264 4.3%
20 kHz 297 296 0.3%
50 kHz 300 298 0.7%
Table 1: Relative HI-3603 Reading (mA/m)
As can be seen, the HI-3603 responds to the non-sinusoidal
waveform fields within 4 percent of the sinusoidal waveform,
showing that it can be used with confidence in VDT-like
waveform fields.
The HI-3603 also provides for monitoring the waveform of the
signal coming from the sensor preamplifier circuit in the input
module. This signal is available from the phono jack located at
the bottom of the instrument. Connection of an oscilloscope to
this jack will allow observation of the preamplifier output. Figures
3 and 4 illustrate the HI-3603's response to 30 kHz saw-tooth
waveforms for both electric and magnetic fields respectively. The
rise time of this waveform was 9 times the fall time. In each
oscilloscope display, both the applied waveform and the sampled
waveform are shown simultaneously. It can be seen that the
reproduction of the electric field waveform is very clean and
virtually identical to the applied field. In the case of magnetic
fields, the broadbanding circuitry associated with the loop sensor
leads to some distortion in the monitored waveform, principally in
the relatively slowly rising part of the saw-tooth. This comes
about partially because of the tailored frequency response that
attenuates response to signals below about 10 kHz. The fidelity