Banner DF-G1-PR-Q7 Instrukcje Operacyjne Strona 155

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350 Cable Survey System
DPN 402197 © TSS (International) Ltd Page 4 of 26
9.1.2 Sub-sea Electronics Pod
The SEP provides all the power supply, signal processing and communication func-
tions for the sub-sea installation of the 350 System.
9.1.2.1 Analogue-to-Digital Converter
See drawing number 401104 in sub-section 10.
Differential analogue signals from the port coil triad arrive at the input to the SEP on
PL2 pins 3/4 (lateral), pins 5/6 (fore-aft) and pins 7/8 (vertical).
Similarly, the differential analogue signals from the starboard coil triad arrive at the
input to the SEP on PL3 pins 3/4 (lateral), pins 5/6 (fore-aft) and pins 7/8 (vertical).
The connectors PL2 and PL3 also carry the +12V and –12V supplies, used by the
pre-amplifier boards, on pins 9 and 10 respectively.
The SEP uses three separate dual-channel ADCs to perform the analogue-to-digital
conversions. This process happens simultaneously on all six input channels. Each of
the ADCs is identical – drawing 401104-2 shows a single dual-channel arrangement
for the starboard lateral and vertical coils. Drawings 401104-3 and 401104-4 show
the port lateral and vertical coil ADC, and the port/starboard fore-aft coil ADC respec-
tively.
For simplicity, the following description includes only the two ADC channels shown in
drawing 401104-2. The description is also valid for the other channels:
U2/U3 and U4/U5 buffer the differential input signals from each coil before they pass
to their appropriate differential input channels of the ADC U1. Except for the applica-
tion of some low-pass anti-aliasing filtering, no signal processing occurs before the
ADC.
The diode array D1–D8 provides protection for both differential ADC input channels.
The ADC device U1 is an 18-bit dual-channel converter that must receive low-noise
signals and power supplies. The ADC has separate analogue and digital grounds to
support this requirement.
In drawing 401104-2, ‘Region 1a’ is the low-noise analogue section of the ADC board
with all its power supply lines filtered and conditioned. Additionally, the digital signals
that pass between the ADC board and the Processor Board are opto-isolated to
reduce noise conduction.
The serial output from the ADC, which appears at pin 15 of U1, is a multiplexed com-
bination of the two input channels. Pin 13 of U1 supplies a gate-control signal to iden-
tify which of the two input channels is currently being transmitted.
Pin 16 of U1 provides a frame-sync signal to identify the start and end of each 18-bit
ADC output sequence.
Opto-isolators U10 and U11 protect the serial data, gate-control, and frame-sync out-
puts before they pass through a ribbon cable to the Processor Board.
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