Simrad ER60, Operator'S Manual

Page: 32 / 182

Simrad ER60 Operator manual
24
850-164692 / Rev.B
Calibration
Introduction
Purpose
For acoustic surveys where accurate quantitative measurements
are required it is essential that the echo sounder is correctly
calibrated. It is a safe practice to perform the calibration before
and after the survey. If experiences over time show that no
adjustments are necessary, it may be appropriate to reconsider
the need for frequent calibrations. Simrad recommends that
calibration is performed at least once a year, and in areas with
different summer and winter condition at least twice a year.
Calibration principles
During calibration a reference target with known target strength
is lowered into the sound beam, and the measured target
strength is compared with the known target strength. If it is
necessary to adjust the echo sounder, this is performed
automatically by the ER60 calibration software. Since the echo
sounder is digital right from the receiver front end, no analogue
gain adjustment is required.
The reference target is normally a metal sphere. Simrad supplies
a variety of copper spheres, one for each frequency. The sphere
diameter is selected for minimum temperature dependence.
Preparations and transducer maintenance
The transducer is heavily exposed to fouling. Make sure that the
transducer face is painted after installation, and that the paint is
maintained whenever the vessel is in dry dock. Always use an
approved anti-fouling paint.
Depending on the environmental conditions where the vessel
operates, fouling must be removed from time to time. Failing to
do so will degrade the echo sounder performance. Use a soft
piece of wood and remove the fouling carefully. Afterwards, use
a very fine grade emery paper.
Note
Do not remove fouling with a metal tool or wire brush.