Principle Of Operation; Speed Over Ground Measurement; Acoustic Transmission/Reception - JRC JLN-900 Installation And Instruction Manual

Principle of operation

The JLN-900 Log system is actually two more or less independent log systems, one for sensing
speed over ground (SOG), Bottom Track Unit, (BTU), and the other for sensing speed
through water (STW), Water Track Unit (WTU – Assy.).
Although both sensor systems are based on correlation technique, sharing many common
features, the principles are somewhat different. Accordingly, the WTU – Assy. Is described in
its own document.
1

Speed over ground measurement

1.1

Acoustic transmission/reception

The correlation speed log uses acoustic waves in water. The transducer is mounted flush with
the hull, see figure below. Waves are transmitted from the piezo-electric elements into the
water, down to the sea-bed. The sea-bed reflects the signal back to the piezo-electric elements,
which acts as receivers, when not used as transmitters. We use broad antenna lobes because we
are not sensitive to lobe widths, compared to a system using Doppler technique.
Bottom track transmission
Transducer
Hull
S1
Ahead
Hull
S2
Piezo-electric elements
Acoustic beams from transmitting
piezo-electric elements
2-3
Projected bottom area