Honda HE-670 Operation Manual page 10

2. GENERAL IMFORATION OF ECHO SOUNDER/FISH FINDER
THEORY OF ECHO SOUNDER/FISH FINDER
Theory of echo sounder/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.
Echo sounder/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.
Round trip
0.5 sec.
Round trip
1 sec.
Displayed image
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 is
formed.
Transducer
Reflected wave from
fish school
Reflected wave from
sea bottom
0
10
20
30
40
5
The speed at which the ultrasonic
wave propagates in water is
approximately 1,500m per second.
For example, in case of roundtrip time
between transmission and reception
is 1 sec. to sea bottom and 0.5 sec. to
fish school,
Distance to sea bottom
1,500m (1 sec.)
2 (round-trip)
Distance to fish school
750m (0.5 sec.)
2 (round-trip)
=750m
=375m