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ELECTRIC ALTIMETER
AIRPLANES WITH AIR DATA VSI
Air Data System No. 1 Schematic (No. 2 Typical)
Figure 4 (Sheet 3)
A 737-300/400/500MAINTENANCE MANUAL
DIGITALARINC 429DATA WORD SOURCE BUS ADC-
L1 R1 L2 L3 R3 L3+R3 L4 R4
DESTINATION AFCC BFCC INDTASSAT/TAT/ NO. 1WARNSTALL NO. 2WARNSTALL A/T 1IRU FMC 2IRU
206 COMPUTED AIRSPEED205 MACH204 BARO-CORRECTED ALT-1203 ALTITUDE XXXX XXXX XXXX X XXXX X
213 STATIC AIR TEMPERATURE212 ALTITUDE RATE211 TOTAL AIR TEMPERATURE210 TRUE AIRSPEED XX XX XXX XXX XX XXXX XX
242 TOTAL AIR PRESSURE220 BARO-CORRECTED ALT-2217 STATIC AIR PRESSURE XX XX X X X X
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737-300/400/500MAINTENANCE MANUAL
B. The computer consists of two pressure transducers, 11 plug-in printed circuit cards, a power supply and chassis assembly. The front panel (Fig. 1) provides two switches for self-test actuation, a self-test indicator light, a fault isolation test connector for off-aircraft trouble shooting and pitot static pressure input connectors. Two electrical connectors mounted on the back of the chassis provide interconnection with the airplane wiring.
C. The TEST SELECT switch manually selects built-in test to be performed as follows: FUNCTION - transmits fixed values on all the computer signal output lines. SLEW - sets altitude rate to 600 feet per minute. FAIL - activates all failure warning outputs.
The PUSH TO TEST pushbutton switch initiates the built-in test and the TEST VALID WHEN LIT indicator light comes on within 2 seconds after manually activated test is successfully completed and remains on if there is no failure.
9. Operation
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A. General
(1)
The air data computer system is depicted in the block diagrams (Fig. 2 and 3), system schematic (Fig. 4) and system interface diagrams (Fig. 5, 6 and 7).
(2)
Power input to DADC No. 1 is shown on Fig. 4 and is supplied from P18 circuit breaker panel. Power input to DADC No. 2 is shown on Fig. 7 and is supplied from P6 circuit breaker panel.
(3)
The digital air data computer (DADC) performs the computations on the three sensed inputs. They are static pressure (Ps) and total pressure (Pt) derived from the pitot static system and temperature from the temperature probe.
B. Pressure Transducer and Temperature Sensing
(1) Each pressure transducer converts pneumatic pressure to digital data. The sensor element is a piezoresistive unit and functions as a strain gage. The resistance varies with pressure applied to the transducer assembly. The temperature probe is a resistance that varies as a function of temperature. The resultant resistance is converted to a voltage. All three analog signals are multiplexed and converted to digital in the analog to digital (A/D) converter and applied to the microcomputer.
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737-300/400/500MAINTENANCE MANUAL
Altitude Synchro Simulation
(1)
The microcomputer sends the digital representation of altitude to a digital to analog (D/A) converter. The resultant analog signal is the dc equivalent of altitude which is demultiplexed and sent to a sample and hold circuit. The representative dc voltages are routed to a sine and cosine generator, modulated by V ref ac and developed by a Scott T transformer into X and Y synchro-type signals. The output is a simulated synchro signal equivalent to the airplanes course or fine altitude.
Airspeed and Mach Synchro Simulation
(1)
The airspeed and mach outputs are produced by methods similar to the
altitude outputs.Baro Correction Altitude 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：737-300 400 500 AMM 飞机维护手册 导航 NAVIGATION 1(67)
