Scope; Equipment Needed; Test Procedure For Bottom Track (Ground Speed); Sog Transducer Angle Calibration - JRC JLN-900 Installation And Instruction Manual

1

Scope

This document describes the Calibration procedures and also serves as a Sea Acceptance Test (SAT)
for JLN-900 Speed Log. The SAT for JLN-900 Speed Log is used to verify that the system works, and
to calibrate the log. The document contains a list of equipment needed, how to perform the test and a
test protocol.
To aid future customer support, it is necessary that two sets of the protocol pages are filled-in. One set
should be returned to JRC and the other set should be left in the reference manual on board the ship.
2

Equipment needed

In addition to the log system, the following equipment is needed:
The log system must have a Speed Log Master Display such as an NWW-82 Main Display
with two-way communication to access the different menu systems.
Display unit for speed and distance indication (such as NWW-82 Main Display). The Speed
Log Master Display can be used.
This SAT instruction.
For the STW log calibration a test site is needed, where accurate distance and speed trials can
be made.
A reference positioning system if the speed over the ground log is to be calibrated. Note!
Calibration of the SOG log is hard to perform and is normally not done on merchant ships. If
DGPS is used as positioning system, always compare it with BTR distance, bottom track
resulting distance, and the SOG log must be within depth range and indicate speed for the total
distance accumulation.
3

Test procedure for bottom track (ground speed)

Ensure that the bottom track log locks on bottom within measurement range and indicate speed.

3.1 SOG Transducer angle calibration

If the SOG shows a transversal speed bias (= the transversal distance trip counter accumulates false
distance) when no drift is present, the transducer alignment may be adjusted. There are two ways to
compensate for the transducer angle.
We strongly recommend the method in which the transducer is mechanically accurately aligned by
test runs.
If this is not possible, there is also an alternative way to compensate the angle in software by adjusting
the calibration angle.
To align the transducer represents an even harder problem in finding accurate enough reference
systems. In some installations, where two axis speed is fed to an integrated navigation system together
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