ETS-Lindgren HI-4456 Isotropic Electric Field Probe (Archived) - Manual (Page 22)

HI n 4456 Manual Page — 17
Probe Operation
Receiver commands to the probe consist of the following:
Send reading Read battery voltage
Zero Set sleep timer
Switch range Read temperature
Enable axis
The signal flow within the probe is shown in the block
diagram.
To measure field strength, three mutually orthogonal
dipole antennas (one per axis) are used to provide an
isotropic response to the ambient field. The signal from
each axis is fed to a Schottky diode detector operating in
its Square-Law region. After filtering, the signals
generated by each axis are added vectorially: the
resultant is fed to the instrumentation amplifier, whose
output feeds the selectable range/offset stage.
NOTE
The HI n 4456 does not allow the option of measuring on
an individual axis: all three axes are active at all times.
Consequently, the axis keypads on the front panel of the
HI n 4416 System Readout have no effect when an
HI n 4456 is connected to it.
For each of the four ranges, the selectable range and
offset stage provides a coarse analog zero for the
measured signal. The output of the range/offset stage is
fed to the A/D multiplexer, then to the analog-to-digital
(A/D) converter itself.
After acquiring the composite three-axis signal, the
microprocessor commands the A/D multiplexer to read
the battery voltage and temperature sensing lines.
Archived 4/2/10