2021-06-24
Page 7 of 40
CU-M001 User manual
CHAPTER 1: INTRODUCTION
DL2 Introduction
The dual axis Doppler speed log system (DL2) 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 DL2 system sends from both beams 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 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 (JB70D2-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.