Single beam
multi beam
What is sound?
Sound is not a thing, nor is it matter.
It is a process of oscillation or vibration.
It is produce by a sound generator such as... Horn,
musical instrument, which puts adjoining particles of
the ambient medium (gases, fluids or solid bodies) into
vibration.
Propogation of sound:
When a particle is induced to oscillate, it pushes
or pulls its neighbors and transmits the
oscillating energy to them.
In this way the oscillation spreads from particle
to particle, in every direction, without the
particles changing their location. Thus in sound
propagation, it is the energy that is transported,
not mass.
Number of oscilations
Frequency:The number of oscillations ,or the number
of vawes produced in one second.
-1000 oscillations or cycles are called one kilocyle
-The human ear senses oscillations between about 16
and 20000 cycles per second.
-Oscillations theat have a frequency of more than
20000 c/s ,whisch the human ear does not hear are
termed Ultrasound.
In echo sounding “ultrasound” is used.
Velocity of Sound
Velocity of sound vawe is different in each medium.
In water(fluid) sound propagated more quickly than air.
In steel it propagated more quickly than water.
No sound is propagated in a vacum.
Air 1000 feet /sec
Water 4500 feet/sec
Iron 15300feet/sec
Distance travelled =(velocityX Time)/2
Velocity=1500m/s in salt water
Time=time taken for the return journey in seconds
Distance=depth beneath the transducer in metres.
************************************************
Time=1 second, depth=750 m,
Time=0.1 second, depth=75 m.
Forms of the transmitted acoustic energy
1- A continous vawe system,
-needs two transducers,
-phase difference between the transmitted and returned
signals is used to calculate the depth.
2-The pulse system,
-rapid, short, high intensity pulses are transmitted and
received by a single transducer.
-is used widely
The Transducer:
The transducer is a converter of energy
Types of transducers:
1-Magnetostrictive
2-Electrostrictive
Magnetostrictive Transducer:
-a bar of ferromagnetic material is wounded by acoil..
-A large current is passed through the coil resulting
magnetic field produced.
-this will couse the bar to change in length
-Nickel is used.
Electrostrictive Transducer
(Piezo-electric)
Certain materials such as Rochelle salt and quartz,
exhibitpressure electric effects when they are subjected
to mechanical stress.
Displays:
1-The chart recorder:
-provide a past record of depth indication.
IMO resolution A224(VII) performance
standards for echo sounding equipment
“The primary presentationshould be a
graphical display which provides the immediate
depth and a visible record of sounding.
The record should show at least 15 minute of
soundings.”
When an electrical current
is sent for transmission,
a stylus conduct conducts an
electrical current through
the paper to the metal desk.
The electrical chargeburns
a nonconductive coating
off the special paper,
leaving a trace on the graph.
When signal returns,the
stylus once again passes an
electrical charge through
the paper to the metal desk,
leaving a second trace on
the graph.
The Digital Display:
Unable to provide a past record of depth indication.
The Rotating l.e.d. Display
Visual Display Unit (VDU)
Echoes are processed and digitized, and displayed in
many different colours and arrangements. The colour
is a function of echo intensity.
Most echo sounders are capable of indicating depth in
Fathoms, Feet or Meters
Controls of Echo Sounders.
Illumination Control.
The illumination control provides continuous
regulation of the illumination of the echogram and the
front panel controls.
.
Receiver Gain Control.
This control regulates the amplification of the received
signals.
Range Selector.
This control selects the basic ranges according to the
table given under technical specifications. In position
0 the recorder is switched off and the depth will be
shown only on the digital depth indicator. The depth
warning and any remote depth indicators will be
operational
Maintenance:
The transducers must not be painted,sanded and
scrapped.
Multiple echoes