Honeywell BENDIX/KING KAP 140 Maintenance Manual page 78

motor via the internal servo amplifier. The command high input is a +/-- 10V signal (through a
2Kohm series resistor) generated by the KC 140 Flight computer. The command low input is a
reference back to an internal KC 140 Flight computer ground. The value of the output signal
determines how fast the servo is driven. Anything greater than +/--9 volts will command full speed
servo movement. The servo can be commanded to drive in either direction through the ANALOG
OUTPUTS diagnostic interface.
To be able to move the controls, the servo clutch must be engaged.
The TRIM_SENSE servo outputs are generated by a strain gauge inside the KS 270C. The strain
gauge produces a voltage based on the amount of torque measured on the pinion of the KS 270C.
This voltage is amplified and buffered to provide a +/-- 3V signal that is proportional to the torque.
If the trim sense + output is +1.2V, then the trim sense -- output is --1.2V. These signals are then
referenced to 3V, so the voltage measured at the servo, with respect to ground, would be +4.2V
and +1.8V. The differential voltage measured from trim sense + to trim sense -- has a scale factor
of 100mV per inch--pound of torque. This strain gauge output is used to determine when trim needs
to run in AP mode. (i.e. If the AP mode is engaged, the trim servo will start to run after a certain
value is exceeded on the trim sense output.)
The TACH output of the pitch servo is a differential +/--5V signal that is used in certain flavors of
the KC 140 to determine when the acceleration monitor should be disabled. The scale factor for
the tachometer output is approximately 0.6V per volt of command drive. (e.g. If you provide 8V of
command drive to the pitch servo you will generate approximately 4.8V of tachometer output.)
The PITCH_SERVO_VALID signal from the KS 270C is used by the KC 140 to determine if the
pitch servo is working properly. If this output is grounded, the pitch servo is valid. If this output
is open, the pitch servo is invalid. This output is routed to the KC 140 Open/Ground discrete input
PITCH_SERVO_VALID. When it is invalid, the KC 140 locks out operation of the pitch axis.
NOTE: If there is less than 0.1V on the low side clutch, when it is engaged and AP DISC is not
pressed, there is a possibility that the low side clutch has inadvertently been shorted to ground and
pre--flight test will fail, since the clutch current is monitored by the KC 140.
The TRIM_SENSE and PITCH_TACH inputs can be viewed on the ANALOG VOLTAGE INPUTS
diagnostic page.
DIAGNOSTIC NAME
Trim Sense
Pitch Tach
Revision 2, Dec/2002
CS:15574F02.IDU
BENDIX/KING
KAP 140
NOTE
SCALE FACTOR
100 mV/in--lb
1 V/V
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