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GENERAL IMFORATION OF FISH FINDER
1. THEORY OF 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 1,500m 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 =1500m/sec. X 1sec.
=1500m
Actually it’s half is depth,
Depth =1500m ÷2
=750m
In case of roundtrip time between transmission
and reception is 0.5 sec. to fish school,
Roundtrip distance =1500m/sec. X 0.5 sec.
=750m
Actually it’s half is depth,
Depth =750m ÷2
=375m
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.
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