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Page 3-6 Robertson AP45 Autopilot
Design and theory of operation
Simrad Robertson AS
Egersund - Norway
The J45A operates reversible hydraulic power units with variable speed control
(RPU80, RPU160, RPU200 and HLD2000) and reversible electro mechanical
power units (MRD100). The unit consists of a printed circuit board with terminal
block, fuse, motor drive electronics and reversing relay mounted in the same type
of aluminium cabinet as the J45S.
Rudder commands from AP45 Control Unit to IC3 A and B makes the relay RL1
change the polarity to the motor. IC2A ensures the motor brake is switched on by
T2 when there is no rudder commands from AP45. IC2A also controls a “dead
time” (delay) to ensure the RL1 relay contacts have physically changed position
before voltage is applied to the motor. This prevents arcing of relay contacts.
Adjusting RV1, preset speed, the output pulse width is decreased/increased, hence
the voltage (RMS) to the motor is changed, adjustable 0-12V.
Connecting straps S1 and S2 provides adjustable 0-24V output for 24V drive units.
Connecting an external strap from terminal 2 to 4 will enable a “Soft start”
function, which reduces the start current and is recommended for the most
powerful drive units like RPU200, RPU300, HLD2000LD and MRD100.
Fig. 3-8
J45A principle
J45A Electronic
Junction Unit