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A – Operating Theory
how the 440 System derives the signal voltage from these measurements for use in the calculation
process.
The SEP applies this measurement cycle to each channel sequentially as shown in
Figure
A-3.
The measurement cycle for each channel lasts a total of 3125µs. With measurements repeated on four
channels, it follows that the SEP measures each channel every 12500µs, or 80 times per second.
Figure A-3: Sequence of consecutive measurement cycles
A.2.2 Derivation of Signal Voltage
After the SEP has measured each channel eight times, it determines the mean value for the eight
preceding occurrences of Sample Region 1 and Sample Region 2. It then subtracts the mean value for
Sample Region 3 from the mean values for Sample Region 1 and 2, and this final figure represents the
two signal voltages for the specific channel.
Each channel therefore has its signal strength values updated ten times per second.
A.2.3 Seawater Rejection
A.2.3.1 Introduction
The Teledyne TSS 440 system represents a considerable advance over the familiar 340 system in that
signal processing routines are used which can discriminate between seawater and metallic targets.
This discrimination is important, because the seawater response seen by the coils varies with the
height of the vehicle above the sea bed. This variability means that it cannot be rejected by the simple
background compensation routines used in the 340.
See
section 6.3.4 "Seawater Compensation" on page 6-16
for an explanation on Seawater
Temperature and setting it correctly.
A-4
© Teledyne TSS
DPN 402196 Issue 4.1
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