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ELEVATOR CONTROL -ELEVATOR ASSEMBLY
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ELEVATOR CONTROL -FUNCTIONAL DESCRIPTION
General
The pitch control system for the elevators uses input command signals from the control column position transducers and the force transducers.
The ACEs receive the input signals and transmit them to the PFCs. The ACEs supply output command signals to the elevator feel actuators and the elevator PCUs.
Control Column Position Transducers
The C and R ACEs each receive signals from two control column position transducers. L1 and L2 ACEs receive signals from only one transducer. After they change the signals to digital format, the ACEs send these signals to the PFCs through the flight controls ARINC 629 buses.
Force Transducers
Each ACE receives one input from the four force transducer LVDTs. The ACEs change and transmit these signals to the PFCs.
Elevator Feel Actuators
The L2 ACE controls the left elevator feel actuator and the C ACE controls the right one.
Elevator PCUs
Each ACE sends output commands to the assigned elevator PCU. It also sends control signals to the adjacent PCU on the same elevator. The pitch command goes to the EHSV. A control signal goes to the bypass and number one blocking solenoid. It sends pressure reducing and blocking solenoid signals to the adjacent PCU on the same elevator.
The PCU sends feedback signals to its assigned ACE from:
*
The EHSV position LVDT
*
The actuator piston position LVDT
*
The actuator null LVDT
*
The differential pressure LVDT.
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ELEVATOR CONTROL -FUNCTIONAL DESCRIPTION -ACE SERVO LOOP
General
The ACE contains a servo loop circuit to give the command signals to the PCUs.
In normal and secondary mode, the PFC sends the command signals to the ACE. In direct mode, the ACE calculates the command signals.
Servo Loop Operation
The elevator command signals go through a servo loop in the ACEs. The command signals then go to the EHSV of the PCUs. The ACEs also use the command signals to monitor for failures. The movement of the EHSV sends hydraulic pressure to extend or retract the actuator.
The EHSV LVDT measures the movement of the EHSV and supplies a feedback signal to the ACEs. The ACEs use this feedback signal to monitor failures.
The actuator position LVDT measures the movement of the actuator and supplies a signal to the actuator null LVDT.
The actuator null LVDT is in series with the actuator position LVDT. The actuator null LVDT modifies the signal from the actuator position LVDT.
The actuator null LVDT supplies a feedback signal to the ACEs to close the servo loop. The ACEs use this feedback signal to monitor for failures. This signal also goes to the PFC.
A differential pressure LVDT measures the differential pressure across the actuator. The signal from the differential pressure LVDT goes to the ACEs for the servo loop. The signal also goes to the PFCs for force fight equalization.
Failure Monitor
The ACE has a failure monitor to check the proper operation of the PCU. The monitor uses the ACE command signal and the feedback signals from the EHSV LVDT and the actuator LVDT. When the failure monitor finds a fault with the PCU or the ACE, it de-energizes the PCU bypass, blocking and pressure reducer solenoids.
Training Information Point
During installation of the elevator PCU, it is necessary to adjust the actuator null LVDT. Remove the null LVDT access cover to adjust the null LVDT.
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ELEVATOR CONTROL -FUNCTIONAL DESCRIPTION -ACE SERVO LOOP
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777 AIRCRAFT MAINTENANCE MANUAL
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