Si-tex SP38, Installation And Operation Manual, Page: 106 / 193

Sitex SP38 Installation and Operation Getting Started
Document PN 29010101 V1r0
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 However the setup may also fail if the HO-HO time is too
slow (more than ~22 seconds), because the autopilot will not
be able to control the Heading of the boat properly.
In either case, you will need to make some changes to the drive system, to slow it
down or speed it up, as determined by your specific application.
If the drive system is a reversing motor (in a hydraulic or cable drive system), and it did
not test as too slow, you will see an option to have the autopilot slow down the rudder
intentionally.
Slowing it down is done by using Pulse Width Modulation (PWM) on the SPU’s drive
output voltages. PWM in effect lowers the voltage “seen” by your drive system’s motor(s),
and thus slows down the rudder’s HO-HO time.
On most boats, it is probably not necessary to slow down the rudder, unless the
HO-HO time is less than ~10 seconds. However, every vessel is different, and so the
choice is left up to you.
If you do choose to slow it down, the rudder movement will be re-tested (in the same
sequence of test steps that you just did), but with it slowed down using a PWM signal that
should run the motor(s) at about 65% of full speed (i.e., the HO-HO time should be ~50%
longer than at full speed).
If this happens, but you still wish the autopilot to slow down the rudder, you may have
to re-route the wiring, and/or use better (possibly shielded) wiring, and/or take other
typical “noise reduction” steps. Contact your Sitex Dealer for assistance.
When Drive Setup is all done, record the settings and choices you made, in Settings -
Compass Setup – Dockside
NOTE: Slow-down is automatically selected for Stern Drive boats when operating using
the “Hi” Parameter Set. Also, Pulse Width Modulation may increase the electrical “noise”
emitted from the drive system’s wiring, potentially causing interference with other
equipment.