ETS-Lindgren HI-4457 Isotropic Magnetic Field Probe (Archived) - Manual (Page 22)

HI n 4457 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 loop
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 4457 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 4457 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
Archived 4/2/10