(b)
LVDT fault ball
1) Each channel of the dual channel LVDT is sent to one RRCM. Circuitry continuously monitors the LVDT secondary element common mode sum voltage to 2.5 volts ac. The fault ball will set if voltage is less.
(c)
PCA fault ball
1) The PCA fault ball is set by any of three independent logic signals. Latching of the hardover monitor, (dual channel failure or low hydraulic pressure inhibits this fault ball signal), failure of both modules within 2.5 seconds of each other, and latching of the open load monitor.
(d)
Module fault ball
1) Fault ball will set if the difference monitor latches and the PCA fault ball dual channel failure signal is not received within 2.5 seconds.
(e)
Test Fail fault ball
1) Failure of BITE test or returning the test switch to NORMAL before test is complete will set the fault ball.
(f)
Reset function provides a reset signal to a set of latches. The latch provides a ground for a 28 volt dc circuit to reset the fault ball.
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757 MAINTENANCE MANUAL
(19) Rudder Ratio Changer Actuator (RRCA) (Fig. 17)
____________________________________
(a)
The left hydraulic system supplies power to operate the RRCA. The system is controlled by the FLT CONTROL SHUTOFF switch L on the right side panel P61. When the engage relay is activated, the solenoid valve is driven to the powered position and ports left hydraulic pressure to the actuator bypass valve and the electrohydraulic servo valve (EHSV). The hydraulic pressure causes the actuator bypass valve to open a fluid path to the PCA port for left hydraulic power and a fluid path from the EHSV to the piston. The EHSV directs hydraulic fluid to extend or retract the piston when a signal is received from an RRCM. The actuator is mechanically biased to maintain the actuator in the retract position (low airspeed condition) in the event of hydraulic system loss.
(b)
As airspeed increases, a signal causes the EHSV to port pressure to extend the actuator. An LVDT on the ratio changer mechanism provides position feedback to the RRCM to stop the piston in the desired position. As airspeed decreases, the EHSV ports pressure from the extend side of the actuator to the return line. Since the actuator always has hydraulic pressure to the retract side, it will move towards the low airspeed position.
(20)
Linear Variable Displacement Transmitter (LVDT) (Fig. 15)
_______________________________________________
(a) The LVDT is driven by the right output crank. As the ratio changer actuator extends, it causes the left output crank to swing inward. The interconnect rod between the cranks causes the right output crank to swing in also. The LVDT piston rod end attached to the right crank is pushed in, so changing the output signal to the RRCMs.
B. Built In Test Equipment (BITE)______________________________
(1)
BITE can be used to test each of the two RRCMs. Use the procedure that follows to do the test:
(a)
Provide electrical power (AMM 24-22-00/201).
WARNING: TO PREVENT INJURY OR DAMAGE, KEEP ALL PERSONNEL AND
_______ EQUIPMENT CLEAR OF ALL CONTROL SURFACES BEFORE PROVIDING HYDRAULIC POWER. AILERONS, ELEVATORS, RUDDER, TRAILING EDGE FLAPS, LEADING EDGE SLATS, STABILIZERS, AND SPOILERS ARE FULLY POWERED.
(b) Provide left hydraulic system power (AMM 29-11-00/201).
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MAINTENANCE MANUAL
(c)
Open access door 119AL and access panel 324BL (AMM 06-41-00/201 AMM 06-42-00/201).
(d)
Place one rudder ratio changer module (RRCM) test switch to TEST. RRCMs are located on equipment shelves E3 and E4. 1) Check that IN TEST light on RRCM remains on for no more
than 18 seconds. 2) Check ratio changer actuator fully extends. 3) Check TEST FAIL faultball does not set. 中國航空網(wǎng) m.k6050.com 航空翻譯 www.aviation.cn 本文鏈接地址：757 AMM 飛機維護手冊 飛行操縱 FLIGHT CONTROLS 1(140)
