1) Serial ARINC 429 bus inputs are converted to parallel and stored in dedicated memory. Analog discrete inputs consists of two types: open/ground and 28v dc/ground. The input level changers convert these signals into transistor to transistor logic compatible format. This is done by equating an open or 28v dc to a logical one and ground to a logical zero. The 48 level changed lines are formed into three 16-bit words. They are input along with a 16-bit internal discrete word into a one of four selector. The computer then selects the desired word for input by addressing the appropriate location. Analog inputs are selected one at a time. They are changed to a digital code in the hybrid Analog to Digital (A/D) converter for use in the digital processing section of the computer. When the conversion is complete, the digital value is stored in dedicated memory.
(b)
Output Interface
1) The ARINC 429 transmitter receives 8 words at a time. These words are then transmitted serially on the 429 output bus. Analog discrete data is latched to the output register and then level changed to a voltage compatible to the airplane. These become the analog discrete outputs. Digital data is routed to the D/A converter and then multiplexed to one of eight Sample and Hold (S/H) circuits which provide the analog outputs. Two S/H provide A/T servo command outputs to the power servo amplifier on the power supply; however, only one is used. Two S/H are used for BIT (D/A wrap around) and two are used for testing. Two S/H are spares.
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(c) Failure Protection and Maintenance 1) The TMC provides failure protection to assure system safety, and maintenance functions that isolate faults to a specific LRU of the TMS or interfacing system. Failure protection and maintenance activities of the TMC are classified as fault data management, interface verification test, and maintenance functional tests. 2) The primary function of fault data management is to support system safety. Fault data management runs continuously when the TMC is powered except during maintenance functional test. It interrogates all system monitors and runs self-test routines as required to prevent computing a false thrust limit or issuing an invalid servo command. When a fault is detected, fault data management responds appropriately to the type of fault and operational mode. It also suppots maintenance activities by performing fault isolation and by storing TMC fault information in nonvolatile memory. It continually transmits fault data to the Maintenance Control Display Panel (MCDP). When activated by touchdown, the MCDP stores the fault data for later display to maintenance personnel. 3) The interface verification test verifies that all input/output lines between the TMC and interfacing components are connected. It consists of passive and active tests. Passive tests are performed without interfering with the normal operation of the TMC. Active tests require the TMC to change the state of its outputs to verify connections. The active tests are part of the maintenance functional tests.
4) The maintenance functional tests provide the capability for performing TMS tests. The maintenance functional test mode is selected when the MCDP is placed in the GRD TEST mode. Maintenance personnel then select specific test(s) to be run via an MCDP input. The TMC then runs the test and transmits the results to the MCDP for display to the operator. The test may require operator action or verification of results. These tests can only be initiated when the airplane is on the ground.
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