27-B
97MU001-F
ANTHEA OPERATION AND INSTALLATION MANUAL
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4.1 LOG CALIBRATION
An E/M log measures speed and distance in relation to water. When there is no current, the
distance indicated by the log is the distance in relation to the bottom or the true distance.
Several methods can be used:
a)
Empirical method
Using the average of the measurements of long distances covered in comparison with
the actual distances.
b)
Rational method
Using the measurements of speed in covering the same base distance several times.
The device is set for the average sensitivity of its sensors in the factory.
If the first method is used, calculate the average relative error for a certain number of runs at
different times and with different tide levels, but at roughly the same speed.
It is convenient to calculate these errors in percentages. The average error is calculated by
taking the average of the relative errors. A large enough number of runs must be made, as in
the following tables :
Runs listed
by order
1
2
3
4
5
6
7
8
9
10
Error
- 2%
- 5%
+ 7%
- 6%
+ 2%
+ 1%
+ 4%
+ 3%
+ 1%
+ 3%
- 2 - 5 + 7 - 6 + 2 + 1 + 4 + 3 + 1 + 3 = + 8
The average relative error is
8
10
= + 0,8 %
The correction is: - 0,8 %
