Skipper CU-M001-21-SA, User Manual

Page: 7 / 38

2021-06-24
Page 7 of 38
CU-M001 User manual
CHAPTER 1: INTRODUCTION
DL21 Introduction
The Dual and single axis Doppler speed log system (DL21) works by the Doppler principle. This
principle is that a sound bouncing off a moving object will change in frequency. This principle can
be utilized by making a narrow beam of sound and analyzing the frequency of the returning sound.
This frequency change is proportional to the relative speed of the reflecting object.
On a vessel, a transducer is positioned pointing slightly in one direction and the reflected sound
comes from particles in the water (STW) and the bottom (SOG). The frequency of these echoes
is translated to speed. By having 2 transducers pointing in 90 deg directions, the speed can be
measured in two axis.
The DL21 sensor sends from both beams and both sensors at the same time. The transducers are
moulded into the same sensor head together with the amplifiers and detection circuitry (transceiver).
In addition, the sensor sends at two frequencies giving accurate values. The DL1 part of the system
is independant and isolated. It also uses 2 beams at a higher frequency, pointed ahead and AFT.
The system is default configured to show STW from the DL1 part of the system, and SOG (2 axis)
from the DL2 part of the system. The DL2 part can be reconfigured to also show the STW (2 Axis)
from the DL2 part, but this may cause a little confusion if the ahead speeds are slightly different due
to the DL1 measuring slightly closer to the Hull
The sensor also contains temperature sensors and tilt sensors to allow compensation of the data.
The transceiver contains a small computer which processes the data and signals and converts them
to speeds. This data is sent to the electronic unit (JB70D21-XX) where it is formatted transferred
to the display and presented on screen , and as data in formats to be integrated into the vessels
navigation and presentation systems such as repeaters and conning. this manual is for the DL2
graphic display part of the system, the DL1 part is covered in a different manual