A320飞机维护手册 AMM NAVIGATION 导航2(145)

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R  - the detector outputs of the LOC and G/S receivers are split 
R  into separate but identical channels. The deviation 
R  calculations are then performed identically by the two 
R  distinct DSPs, each channel being independent and 
R  self-supporting with separate clocks and support logic 
R  - the I/O processor then compares the deviation calculations 
R  from the primary DSP against those from the monitor DSP, and 
R  sets the SSM to NCD, FW or NO, depending on the comparison 
R  results, before sending them to the output UART. 
R  4_  ARINC output monitoring
R  The ARINC 429 output data are monitored by: 
R  - the DSPs: 
R  If no correct deviation data are fed back, the DSP (as 
R  detailed in para. (3)(c)) shuts the output bus off. 
R  - the system processor, via a monitor UART: 
R  Any input to the UART that does not have proper parity is 
R  discarded. 

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R  Thus, any altered word is rejected and not seen by the 
R  system processor which checks the output every 10 ms. 
R  If no LOC or G/S deviation word is received within 400 ms, 
R  the output bus is shut off also by the system processor. 
R  Whenever the bus is shut off by the DSPs only, it can be 
R  recovered clearing the fault-inducing condition. 
R  If the bus is cut off by the system processor, it remains cut 
R  off until power is recycled to the ILS. Then the system 
R  processor restarts at the beginning of its program, which 
R  includes a power-on test. 
R  If the fault has not been cleared, the bus is shut off again. 
R  5_  ARINC 429 input
R  The selected input ARINC bus is monitored for valid labels, 
R  SDI, word rate and odd parity: 
R  - words with invalid label or SDI are ignored 
R  - concerning frequency data, if the word is received for a 
R  period greater than 450 ms or if the data do not contain a 
R  valid ILS frequency (which means SSM to Normal Operation 
R  (NO) and existing ILS channel), the output frequency word is 
R  set to NCD. In fact, unless two consecutive valid input 
R  frequency words are received, the ILS holds its last valid 
R  frequency, and sends it out at 5 words per second with an 
R  SSM coded NCD. As described above, the SSM of the input 
R  frequency word is monitored for NCD condition. In this 
R  particular case, the SSMs of the transmitted deviation 
R  output words are forced to NCD. 
R  In all cases, if tune/test inhibit is asserted, frequency 
R  data on the ARINC input is ignored, and the output frequency 
R  word will contain the last valid tune frequency. 
R  6_  Tune/test inhibit discrete input
R  The system processor monitors the two Tune/Test Inhibit (TTI) 
R  inputs and if these inputs are not of opposite states, a 
R  failure warning flag is issued. 
R 
R  7_  Power supply
R  All power supply voltages are monitored continuously by the 
R  system processor for operation within predefined windows. If 
R  these window limits are exceeded, LOC and G/S deviation 
R  outputs are flagged to NCD or FW, depending on the voltages 
R  values, and also of the debounce times. 

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R  (b) Test mode monitoring 
R  - The functional test modes provide a check of all 
R  deviation-affecting circuitry: as described in para. (3), 
R  internally generated RF carriers with known deviation levels 
R  are applied to the receiver inputs. The ILS must then supply an 
R  output word with the expected value of deviation. In this way, 
R  a satisfactory functional test provides confidence that the ILS 
R  is providing correct deviation from modulated RF signals. 
R  - Power-on test (Ref. Para. (3)(f)3_) 
R  - Faults detected during test mode set the SSM of the appropriate 
R  deviation word according to the test result. Once the fault is 
R  cleared, normal operation is resumed. 
　
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