(2) Analog Air Data Computer (P/N 60B00058)
(a)
Two of the modules in each analog air data computer require air pressure information. Static air pressure is routed from the input port to a pressure transducer in the pressure altitude module. Pitot and static pressures are routed to a pressure transducer in the computed airspeed module. The pressure transducers are electrically coupled to their respective computing circuits. Each computer determines pressure altitude from an electrical equivalent of static air pressure and computed airspeed from an electrical equivalent of differential air pressure.
(b)
Total air temperature information is used in the mach number module by each central air data computer. Each total air temperature probe provides a computer with a resistance that varies as a function of total air temperature. The varying resistance controls a temperature amplifier stage output which is coupled into the mach number module as an electrical equivalent of total air temperature.
(c)
The computed airspeed module uses an input representing pitot and static air pressure differential and a static source error correction factor to compute airspeed. Outputs of this module are from two synchros, a hold synchro, and a linear transformer.
(d)
The pressure altitude module uses an input representing static air pressure and a static source error correction factor to compute altitude and altitude rate of change. Outputs of this module are from three coarse and three fine synchros, two hold synchros, an altitude rate amplifier and an altitude reporting digitizer.
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(e)
The mach number module uses an input from the computed airspeed module (a combined function of airspeed and altitude) to compute mach number. Outputs are from one synchro and one hold synchro. Also in this module, each number and total air temperature are combined into the functions of static air temperature and true airspeed by two function generators. The mach number module also combines static source error correction (SSEC) inputs and mach number to produce the SSEC correction factor.
(f)
The true airspeed module uses an input representing true airspeed as computed from the functions of temperature and mach number in the mach number module to position a servo repeater. Outputs of this module are from two synchros and a linear transformer.
(g)
A failure detected by the failure warning logic assembly also triggers a failure annunciator circuit associated with the section of the computer where the failure occurred. A maintenance annunciator on the face of the central air data computer will flip from black to yellow and latch in the yellow condition. Once triggered and latched, this yellow ball is always visible until the annunciator is reset. On airplanes with a -100 computer installed, the computer is partially removed from the shelf and the annunciators reset manually. On airplanes with a -200 computer installed, the computer SELF-TEST switch will reset the failure annunciators.
(3) Digital Air Data Computer (P/N 60B40126 and HG480C1)
(a)
The transducer module is the pneumatic pressure sensing element of the digital air data computer. When sampled by the plug-in modules computer, it updates sensed static pressure Ps and measured total pressure Pt in two electrically temperature-compensated sensor cells. It communicates dc analog voltages of the cell temperatures and pressure errors to the computer plug-in modules electronics.
(b)
The transducer module contains four separate assemblies; a sensor, two electronic converter cards and a motherboard assembly. The sensor houses the static and total pressure assemblies enclosed by a common dual cavity housing and also housed within the sensor is the temperature sensing element for compensation purposes. The electronic converter cards perform the digital-to-analog signal conversion required by the computer sensor loops. The motherboard assembly provides the interconnector between the electronic converter cards and interfaces the transducer with the computer chassis.
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(c) Part of the computer plug-in module circuits measure the conductivity of the total air temperature sensor. The dc multiplexer multiplexs dc voltage analogs of the measured air data from the transducer module, a zero-calibration ground for the central processing unit; and monitor wrap around voltages. The multiplexed dc analog voltages are encoded and placed on the bus by the central processing unit operating in the analog-to-digital mode. Discrete test-initiate commands, SSEC signals, and parameter-hold commands are placed on the bus by a discrete input buffer. The plug-in modules digital computer reads the bus data, computes the required air data functions (and failure warning signals when necessary) and writes the result on the bus in the appropriate time slots. Three discrete-output buffers place digital data from the bus on the discrete signal portion of the computer airframe electrical interface. The central processing unit operating in digital-to-analog mode applies multiplexed dc voltage analogs of all the other computed air data functions to the demultiplexer and sample and hold circuits. The continuous dc analog voltages are applied to analog signal conditioners to generate the synchro-compatible outputs and other analog outputs of the air data computer.
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本文链接地址：747飞机维护手册AMM CHAPTER 34 - NAVIGATION 第34章导航1(58)
