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E2-1
LADC
RADC
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(b) Each module processes these inputs and provides suitable control and fault annunciation signals. The module engages/relaxes the engage relay (if in command) and provides/receives control and engage interlock signals between modules. The module also provides input to the EICAS computer and amber RUDDER RATIO light.
(13) Channel Selection and Interlock_______________________________
(a) The first module to receive a validated airspeed signal from the respective SAM takes control to become the primary channel. This module provides a low logic signal locking the other module in the STANDBY mode. Activation of the engage relay by the module in control provides an engage interlock signal. This signal inhibits the standby module from activating its own engage relay.
(14) Latching Logic - Power up Sequence__________________________________
(a)
During initial power up, the difference and hardover latches are set to low logic (capable of control) for 12.5 seconds. Invalid-to-valid transition of SAM Vp VALID signal includes a 10 to 15 second delay which inhibits the output monitors while system signals are synchronized.
(b)
In the power up sequence, SAM Vp valid signal remains invalid and the control line is high logic. The latch monitors are forced low for 12.5 seconds. Engage relays are de-energized and the amber RUDDER RATIO light is on. SAM Vp VALID signal changes from invalid to valid, forcing the hardover and difference monitors to an inhibit nonfailure state. One module takes control, locking the other module to standby, and inhibits energizing of the other engage relay. The amber light goes out and servo and solenoid valve signals connect the actuator through the solenoid valve. Hydraulic power is applied and the RRCA drives to the commanded position. The output command monitor inhibit is released and tripping function enabled.
(15) Latching Logic - Control and Shutdown_____________________________________
(a) Module in command hardover, difference or open-load monitor tripping causes the control line to go to high logic and de-energizes the engage relay. Control is shifted to the standby module and a white RUDDER RATIO message appears on the EICAS maintenance page.
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(b)
Module on standby hardover, difference or open-load monitor tripping forces the control line to remain in high logic and inhibits passing of control from module in command. A white RUDDER RATIO message is stored on EICAS maintenance page for later display.
(c)
Left system hydraulic pressure loss causes both modules to de-energize their engage relays. Hydraulic shutdown of the actuator follows, causing loss of ratio changer function and cycling of ratio changer to low-speed position. The amber RUDDER RATIO light goes on and a RUDDER RATIO alert message (level C) appears on EICAS display.
(d)
Loss of SAM Vp VALID signal drives the control line high and de-energizes the engage relay and shifts or inhibits shifting of command between modules depending on which module loses the signal.
(16)
Ground Test Logic
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