NARDA 8718B - Manual (Page 82)

81 Chapter 14 Probe Zero
14
Probe Zero
Understanding the Zero Function
The purpose of “zeroing” the probe and meter is to set the meter
to indicate a zero field strength when there is no measurable
field strength. The Narda 8700 series survey system maintains
measurement accuracy under all conditions by insuring that all
probes always provide true RMS (Root Mean Squared)
indications of field strength. Diode detectors, which are used in
many of Narda’s electric field probes, are always operated in the
square law region. Since the diodes are not operated in a
saturated mode to insure accuracy in multi-signal conditions,
the survey system must be “zeroed”.
The Model 8718B establishes the zero reference as a small
positive voltage inside the meter. This zero offset allows the use
of only positive voltages while handling both positive and
negative zero drift. While it is difficult to distinguish between a
positive zero drift and the presence of an actual field, a negative
indication on the meter must be due to zero drift. This is
indicated on the display by a flashing negative sign between the
field strength value and the unit of measure on the second line of
the display.
1 2 . % S D T
2 7 . 5 M A X C F 1 . 0
A L T M A X R M E N U F R E Q
1
F1 F2 F3 F4
0
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