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CM2 Sidescan Sonar User Manual
Counting Pulley
The purpose of the counting pulley is to allow the tow cable scope (i.e. the length currently deployed) to be
displayed to the sonar operator and be recorded within the sonar record.
Note that the cable scope (i.e. the length of cable veered) and layback (the horizontal distance of the towfish
behind the reference point on the vessel) are not the same. The relationship between scope and layback is
complex and depends on the cable and towfish characteristics and on towing speed. Unless a specific cable
scope-to-layback conversion program is available layback must be estimated and entered manually.
Installing the Counting Pulley
The counting pulley consists of a CM2 pulley fitted with a pulley sensor. All CM2 pulleys are all fitted with one
magnet (Types O and S) or two magnets (Type L) so the rotation can be detected at intervals equivalent to
half-metre intervals at the circumference.
The pulley sensor is connected to a PC's serial port via a counting pulley deck cable. Depending on the PC
the deck cable may need to be terminated in a serial-to-USB converter. The PC may be the same PC that is
used with an STR or may be a navigation PC for example.
To install the counting pulley software, install the Counting Pulley Display CD that is supplied with the pulley
sensor, and follow the on-screen instructions.
Locate the pulley in accordance with the advice given in Section 3. Route the counting pulley cable so that it
is not under tension at any point, nor likely to be tripped over.
When the pulley is not in use it is advisable to remove the pulley cable and replace the cap on the pulley
sensor.
The pulley cable connections are as follows: -
Pulley sensor connector...conductor...D-type connector
Version 3.6 (2008)
Pulley Cable Guides
F....red...2
D...black...3
C...white...4
H...screen...5
A...yellow...7
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19. Pulleys and Counting Pulleys
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