Sperry Marine NAVIKNOT 600 SD, Operation, Installation And Service Manual

Page: 152 / 256

056353/J NAVIKNOT 600 SD
7-4 Doppler Transducer Calibration
Zero Point Calibration
Before any entries for non-zero speeds are stored in the calibration table
or calibration trial runs are conducted, the zero point calibration should
be carried out.
The “zero point” refers to the calibration table entry which holds the
uncalibrated (“raw“) speed value corresponding to a true water speed of
zero knots. Two methods are available to calibrate the zero point: man-
ual and auto.
Manual Entry
The manual entry method permits zero point calibration in waters which
are not free of current. However, the longitudinal component of the cur-
rent must be known and it must be small enough to regard the sensor as
operating near zero speed.
Note Both the manual and the automatic zero point calibration require that the
vessel is stationary.
To carry out the manual zero-point calibration:
1. Go to page 2 of the Service Setup;
select the Calibration | Zero Point | Man Calibration sub-menu.
Three values are shown, the true speed, the uncalibrated speed and
the calibration value (i.e. the difference of the two speeds).
The uncalibrated speed is the raw speed value as currently received
from the preamplifier D (not editable).
The objective of the calibration is now to alter the calibration value
until the displayed true speed value matches the known actual water
speed.
Thus, in waters free of current, the displayed true speed value must
be brought to zero; in the presence of current, the true speed value
must be made equal to the known longitudinal component of the
current.
2. With the
Right/Left
arrow
keys, alter the calibration
value until the displayed
true speed exactly
matches the known
actual water speed.
3. Press
ENTER
to confirm
the setting and leave the
manual calibration sub-
menu.
SERVICE SETUP Page 2
CALIBRATION
ZERO POINT
MAN CALIBRATION
-00.2
+00.2
-00.4
KN
KN TRUE SPEED
UNCAL SPEED
CAL VALUE
Note When the manual entry is stored, the true speed entered is automatically
subtracted from both the uncalibrated and true speed values.
Thus, the entry written to the table will always contain the uncalibrated
value corresponding to a true speed of zero knots.