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GENERAL IMFORATION OF FISH FINDER
1. THEORY OF ECHO FISH FINDER
●
Theory of fish finder is same as echo.
Ultrasonic pulses transmitted from the transducer into the water are reflected from fish school or
the sea bottom and then they are received by transducer.
Fish finder converts round-trip time between the time and the ultrasonic wave is transmitted and the
time the reflected wave is received into distance and measures the depth It displays size or density
of fish school, the outline of bottom or nature of bottom on the screen in different colors.
The speed at which the ultrasonic wave propagates in water is approximately
1
,
500
m per second.
You can know the depth to fish school or bottom counting time of roundtrip between transmission
from transducer and reception to transducer.
For example, in case of roundtrip time between
transmission and reception is
1
sec. to sea bottom,
Roundtrip distance =
1500
m/sec. X
1
sec.
=
1500
m
Actually it's half is depth,
Depth =
1500
m
2
=
750
m
In case of roundtrip time between transmission and
reception is
0
.
5
sec. to fish school,
Roundtrip distance =
1500
m/sec. X
0
.
5
sec.
=
750
m
Actually it's half is depth,
Depth =
750
m
2
=
375
m
●
How to show image on fish finder
Each time when image is sent by one line to the left, ultrasonic wave is transmitted and it's reflected
echo is displayed on the right edge of screen. By repeating this, image like longitudinal section in
water is formed. Therefore, latest image just under boat is shown on right edge of screen.
0m
Past image
Present Boat's
Position
10m
20m
30m
40m
Note:
Speed which image moves from right to left is not related with boat's speed.
Round Trip
0.5 sec.
Reflected wave
from fish school
Transducer
Reflected wave
from bottom
Round trip
1 sec.
