Simrad EQ42 Specifications download pdf (Page 19)

EQ33 Echosounder operation Chapter 5-1

5. Echosounder operation

The echosounder function of the EQ33 determines the distance

between its transducer and underwater objects such as fish, lake

bottom or sea bed. It does this by utilizing the fact that an ultrasonic

wave transmitted through water travels at a nearly constant speed

of 1500 meters (4800 feet) per second. When a sound wave strikes

an underwater object such as fish or sea bottom, part of the sound

wave is reflected back toward the source. Thus by calculating the

time difference between the transmission of a sound wave and the

reception of the reflected sound wave, the depth to the object can be

determined.

The entire process begins in the display unit. Transmitter power is

sent to the transducer as a short pulse of electrical energy. The elec-

trical signal produced by the transmitter is converted into an ultra-

sonic signal by the transducer and transmitted into the water. Any

reflected signals from intervening objects (such as a fish school)

are received by the transducer and converted back into an electri-

cal signal. It is then amplified in the amplifier section, and finally,

displayed on the screen.

The picture displayed is made up of a series of vertical scan lines

(pings), one for each transmission. Each line represents a ‘snapshot’

of what has occurred beneath the boat. The series of snapshots are

accumulated side by side across the screen, and the resulting con-

tours of the bottom and fish between the bottom and surface are

displayed.

Selecting echosounder displays

The EQ33 provides various types of echosounder displays: standard

echogram, A-scope, bottom expansion (zoom) and VRM expan-

sion. Each display has its special advantages. Select the appropriate

setup for the echosounder display in the presentation “Setup” and

“Echosounder setup” displays, considering current sea area and

target fish.

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Simrad EQ42 Specifications Page 19