Ks 270C Pitch Servo - Honeywell BENDIX/KING KAP 140 Maintenance Manual

1.5.4 KS 270C PITCH SERVO

The KS 270C pitch primary servo, used to provide AFCS control of the elevators, contains a servo
motor with amplifier and engage clutch, as well as a torque sensor for trim command generation.
The servo outputs a differential trim sense signal with a scale factor of 100mV/in--lb, with a positive
differential voltage representing CW torque. Maximum sensed torque is at least 20 in--lb in each
direction. Pitch servos also contain a tach feedback signal to provide servo motion sensing. The
servo outputs a differential signal with a scale factor of approximately 5.3 V for full servo speed.
In installations using the --27XX, --5201, --54XX, --55XX, --77XX and --79XX FCCs, the tach signal
is used to disable the FCC acceleration monitor when servo motion is not causing the sensed
aircraft acceleration.
Each primary servo is installed with a KM 275 servo mount, which contains a slip clutch for pilot
override. The servo receives a differential command input and drives the servo motor with a speed
proportional to the magnitude of the command. The command polarity will determine direction of
servo rotation. The command inputs have an impedance of at least 15K ohms. The interface is
designed such that an open command signal will not cause a servo drive of more than 25% of
full--scale speed.
The pitch servo also contains a validity circuit which compares the motor voltage against the servo
command. The servo actuator outputs a open/ground discrete signal, where ground represents
a valid servo. If the comparison fails, the servo outputs an invalid (open) signal to the FCC.
Removing power to the servo (e.g. by pressing the AP DISC switch)
will also cause the servo to be sensed as invalid.
Revision 2, Dec/2002
CS:15574F02.IDU
BENDIX/KING
KAP 140
NOTE
FIGURE 1--3 KS 270C PITCH SERVO
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