artisan TRACKPOINT 3 4211A, Operation And Maintenance Manual

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TRACKPOINT 3 PRINCIPLES OF OPERATION
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4.2 TARGET ACQUISITION MODULE
Each of the three clipped signals is sent via current loop to the Peripheral Interface Card and
then to each of the Target Acquisition Modules (4). The phase differences between the leading
edges of the signals are measured and stored for later transmission to the main DSP Card.
When a valid signal is detected (Section 4.3), the Target Acquisition Module transfers the RAM
contents, starting with the most recent phase count data, to the main DSP for processing (Sec-
tion 4.4.)
4.3 DETECTION CIRCUITRY
One of the input signals is used in the detection circuitry. It is mixed with a Local Oscillator,
then fed to a sharply tuned filter. The filter outputs go to a peak detector/threshold system,
which can generate an interrupt for the DSP. The detector outputs also control the front panel
LED's, and the peak detector circuit provides signals for the audio generators. The audio cir-
cuitry provides an indication of the strength of the signal received at the chosen frequency.
4.4 DATA TRANSFER
When the interrupt generated by the detection circuitry is recognized by the DSP, the following
sequence of events occurs, resulting in the transfer of all of the raw data over a high speed se-
rial bus to the main DSP board. All counting and data collection is halted, the VRU, COMPASS,
ANALOG DEPTH and TEMP signals are digitized and stored along with a time tag, and an inter-
rupt is sent to the main DSP board to initiate data transfer. The main DSP board, when ready,
will read the raw data, including VRU, COMPASS, ANALOG DEPTH and TEMP data. At the end of
the transfer, data acquisition can begin again for any other channel (TAM).
4.5 TRANSMIT SIGNAL
Transmitter parameters, such as frequency, repetition rate, and pulse duration, are entered via
the keyboard and immediately sent to the Main TAM, where generation of the transmit signals
occurs. The frequency is latched, and a Phase Lock Loop generates the actual signal. The repe-
tition rate and duration are controlled by a counters within the CPLD. An external input can also
be used to trigger the transmitter (for transponder operation) or Trigger (key) out (for re-
sponder operation) in place of the internal repetition rate generator.
In transponder or responder mode, the transmit signal starts a timer, which is stopped and
read after receipt of a valid reply. This timer determines the transit time which is translated by
the main DSP Card into slant range.