H28470
500  Autopilot Warning Lights Circuit 
Aug 15/68  Figure 13  22-11-0 
Page 49 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

6.  Autopilot Pitch Channel Operation
A.  General
(1)  
The pitch channel provides pitch axis control by amplifying, shaping, computing and coupling error and command signals to drive the elevator control surface through an actuator. (See figure 14.). Error and command signals originate in the input sections, are summed and are processed in the pitch processing section. Intelligence from the pitch processing section is fed to the output section. The output section together with the position feedback and stabilizer trim section further refines pitch channel signals to the proper DC voltage levels necessary to actuate the transfer valve in the appropriate elevator power unit. A lift compensation signal, from the roll channel is also fed directly to the output section.

(2)  
Discussion of the pitch channel operating modes is based on the block diagram shown in figure 15.

B.  Operating Modes
(1)  Synchronization Mode
(a)  Prior to pitch channel engagement, the following functions are provided in the pitch control channel: pitch attitude synchronization, valve amplifier synchronization, and elevator position synchronization. Pitch attitude and valve amplifier synchronization null the valve amplifier output signal, while synchronizing the pitch servo control transformer (CT) to the airplane attitude. The valve amplifier output signal is modulated within the valve amplifier and the resulting 400-cps signal is routed back past open engage switch PS-11 to summing point 2 and the motor control amplifier in the pitch computer.
500 
22-11-0 Page 50  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  May 15/68 

H19104 H19107 H19072
540  Pitch Control Channel Simplified Block Diagram 
Feb 01/74  Figure 14  22-11-0 
Page 51 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

Pitch Control Channel Block Diagram  540 
22-11-0  Figure 15 (Sheet 1)  Feb 01/74 
Page 52 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

506  Pitch Control Channel Block Diagram 
Feb 01/75  Figure 15 (Sheet 2)  22-11-0 
Page 53 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

Output from the motor control amplifier rotates the motor-tachometer generator. This drives the CT through the numerically lower ratio (LO) of a dual ratio gear train. Rotation speed is governed by output from the motor-tachometer generator applied to summing point 2. The CT rotates until the valve amplifier output is nulled. When this output is eliminated, motor-tachometer generator and CT rotation cease, and the rotor position of the CT is synchronized with the airplane pitch attitude sensed by the vertical gyro. Modulated valve amplifier output is also applied to the signal trim monitor. Until pitch attitude and valve amplifier synchronization are complete, the signal at the input to the trim monitor will cause the trim monitor to prevent pitch control channel engagement. Synchronization in this manner eliminates transient pitch commands up on engagement of the pitch control channel.
(b)  Elevator position synchronization is accomplished as follows: Signals from the stabilizer neutral shift sensor and the elevator position transducer are summed at summing points 9 and 10. Output signals from summing point 9 are amplified and fed to the elevator position indicator. The position signals at summing point 10 are summed with the output of a counter/converter (part of a digital synchronizer), and the resultant signal is fed to summing point 3 and past de-energized switch PS-7 to summing point 11. Signals from summing point 11 are sensed by an error detector (part of a digital synchronizer) which feeds clock pulses past de-energized switch PS-13 to the counter/converter. The phasing of the error signal determines whether the clock pulses are added to or subtracted from the count stored in the counter/converter. This is analogous to driving an electromechanical servomechanism in either direction as a function of error signal phase. The counter/converter sends a feedback signal to the error detector when the counter is full to inhibit the clock pulses. This corresponds to driving an electromechanical servomechanism to its mechanical limit. The amplitude of the counter/converter output signal is proportional to the count in the counter. This signal is fed to summing point 10 where it is summed with elevator position and neutral shift sensor signals. During synchronization, the counter/converter output will automatically adjust to a value which reduces the error signal inputs to summing points 11 and 3 to approximately zero. Elevator position synchronization establishes a reference trim position for computation of automatic stabilizer trim commands when the pitch channel is engaged. The reference position information is stored in the counter/converter which does not receive clock pulses when the pitch channel is engaged because of the action of a toggle which is represented in figure 15 by PS-
　
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