AR FI7000, Руководство по эксплуатации и обслуживанию

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Rev F 9
2. THEORY OF OPERATION
2.1 DESIGN OF THE PROBE KIT
The Model PL7004 Probe Kit consists of two principal functional units: the probe and the probe interface.
The two units are connected by two pairs of fiber optic (F/O) cables. Power to operate the probe and
commands to the probe are provided from the interface on one of the F/O cables. Responses from the probe to
the interface are provided on a second F/O cable. The other F/O pair is a safety loopback connection ensuring
properly connected cables prior to laser turn on.
Each probe has been calibrated at the factory in a pulsed field at a single frequency, and the resultant
calibration tables have been loaded into probe non-volatile memory. The calibration tables provide the basis
for the conversion of the digitized signal, from the sensor/detector/pre-amplifier/A to D converter path, to
electric field measurement values for each axis. A composite field level is then derived by calculating the
square root of the sum of the squares of the individual axis field values. This calculation method is generally
quite precise relative to the extent to which all the individual axis antenna patterns are those of very short
electrical dipoles (sine function) at all frequencies.
In addition to the operating program and calibration tables (firmware), each probe’s memory also contains the
serial number of the probe, the revision of the probe’s firmware, and the probe’s most recent calibration date.
The probe interface sits between the probe and the host and provides all of the specified communication
protocols to the host. The two functional units are described in greater detail below.
2.2 PROBES
The probes incorporate three orthogonal sensors, one for each axis, labeled X, Y and Z. The sensors feed
detectors and the detected signals are routed through high-resistance leads to low noise preamplifiers in the
housing. Circuitry within the housing, including a programmed micro-controller, processes the amplified
detected levels to create a stream of digital information light encoded onto a fiber optic cable exiting the
housing. Power (to operate) and commands to the electronic circuitry are received on a second fiber optic
cable.
2.2.1 PL7004 Sensor
Sensors in this probe include simulated tapered resistance monopoles and a diode detector. Sensors, detectors,
and video circuits are housed in protective radomes.
2.2.2 PL7004 Detector
Each sensor is connected to a medium barrier Schottky diode detector. This produces a video signal which is
then processed and measured to provide a peak field measurement.
2.2.3 PL7004 Preamplifier
The detected output of each sensor is fed to an amplitude compressive preamplifier. The response time is
limited by a low pass filter, offering an extended post–detection response-smoothing time constant to stabilize
the reading over the specified operating frequency range.