NT888G MK2 AUTOPILOT OPERATING MANUAL
2.22 Loop Gain Calibration.
(i)
Switch the Autopilot to STANDBY and enter the Set Up Menu per section
2.12 a).
(Vessel now under manual steering control).
(ii) Use the Autopilot Set Course knob to scroll through the Set Up parameters
until ‘LOOP GAIN’ is displayed (4
th
parameter) and read the number of
degrees (1.5
o
, 1.8
o
etc.) displayed in the centre column.
(iii) Rotate the illum. control (+/-) to increase or decrease the value shown (as
required).
(iv) Exit the Set Up Menu (simultaneous 5 sec. operation of CANCEL and
CONFIRM keys).
2.23 Autotrim (Automatic Permanent Helm) Assessment.
Functional
Description.
The Autopilot system is equipped with an Integrator, which enables the electronic
control stages to monitor the instantaneous position of the rudder in the STANDBY
mode and to control the mean position of the rudder in the ON mode.
In the STANDBY mode, the Autotrim (APH) integrator memorises and adopts any
angle of rudder offset (up to 30°) which exists at the instant that the Autopilot is
switched from STANDBY to ON.
This function is always operational when the Autopilot is switched from
STANDBY to ON and permits the Autopilot to copy the angle of offset rudder
manually applied to steer the vessel dead ahead on the desired heading (i.e.
Trim compensated) at the instant of Autopilot engagement.
In the ON mode, the Autotrim (APH) function continuously monitors any long term
differences between the Autopilot Heading Set and the mean course actually steered.
Any apparent long-term difference is compensated for by automatic trim
reassessment over a period of time to ensure the correct mean direction of the vessel
through the water.
NB.
The Autotrim function can be disabled if required by 5 second AUTOTRIM key
operation confirmed by illumination of the corner keypad (OFF) LED.
The Autotrim timing period is factory set at 600 seconds for displacement vessels (10
minutes) and 100 seconds for High Speed Craft for a maximum of 20° of rudder, but
is re-programmable via the Set Up Menu and is identified as Autotrim Secs (9
th
parameter).
APH timing periods of less than 200 seconds (3.3 minutes) are likely to degrade
Autopilot steering performance on vessels other than high-speed craft with
planing/semi planing hull forms. Timing periods greater than 600 seconds may
benefit larger ocean going displacement vessels subject to seagoing appraisal.
