(1)
Sine and cosine voltages from the altitude synchro simulator and baro correction 1 and 2 are sent to the baro-set synchro module and demodulated using the baro altitude ref 1 and ac as reference voltages. The output of the demodulator is buffered and sent to the multiplexer and to the A/D converter. The microcomputer processes the signal and sends it to the Arinc 429 transmitter for transmission on the four Arinc buses (Ref Fig. 5).
Altitude Rate
(1)
The computer determines the airplanes altitude rate and sends it to the D/A converter and demultiplex circuit. The demulitplexed output is developed by the sample and hold circuit and the buffered output is sent from the air data computer as altitude rate.
Airspeed (Q) Pot
(1)
The Q pot receives digitized inputs from the microcomputer. The speed switch (SPD SW) changes state at 190 knots during increasing airspeed and at 170 knots during decreasing airspeed. This results in a step gain change in the output dc reference voltage. The gain output is 1/Q or reciprocal of airspeed which is sent to the yaw damper system.
ATC Altitude Reporting
(1)
The altitude reporting enable signal is produced in the air traffic control (ATC) control panel. Digital altitude is sent from the microcomputer and the representative altitude signal is changed from serial to parallel digitized data and sent to the ATC transponders.
Digital Data Bus (ARINC 429)
(1)
The digital bus module receives the digital output from the microcomputer and translates in into Arinc 429 format. The output on all four buses is the same and consists of the following signals: pressure altitude, baro corrected altitude, mach, CAS, TAS, TAT, SAT, ALT RATE, static air pressure (Ps), total air pressure Pt and a source destination identification (SDI).
(2)
The table of Fig. 5 identifies all digitized bus output and the units receiving this information. For ADC-1 the buses are labled DADC-L1, L2, L3 and L4. For ADC-2 the buses are labled DADC-R1, R2, R3, and R4. A receiver in the units receiving the signals selects only the signals required for that units operation.
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A 737-300/400/500MAINTENANCE MANUAL
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CABIN PRESSURE IS CONNECTED TO DADC 2
Air Data System No. 1 Interface
Figure 6
A 737-300/400/500MAINTENANCE MANUAL
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A
737-300/400/500MAINTENANCE MANUAL
J. Failure Warning
(1)
The computer continually monitors itself. Program timing is monitored by a watch dog timer (WDT) which compares program loop time to the time produced by a reference time clock (Real Time) in the WDT. If a discrepancy appears, the WDT first attempts a restart. If unable to accomplish a restart after 3 consecutive real time intervals a computer shutdown occurs.
(2)
The temperature signal and difference between Pt and Ps are checked for reasonableness. Test programs are run to validate A/D and D/A conversion, Synchro simulator and atitude rate employ wrap-around (W/A) monitoring to ensure adherence to tolerances. The Arinc 429 transmitter is checked to verify accurate translation of parallel digital inputs to serial format.
(3)
The failure warning contains the circuit necessary to drive the flags on the indicators and to operate monitor circuits in the flight control computers. The computer words containing the results of monitor programs are sent on the output bus, buffered, and captured by the latch. The latch output is amplified by drivers which issue the flag output voltage. Failure of one parameter causes all flag outputs to indicate failure, the master failure relay (K1) to energize, and the TEST VALID WHEN LIT light on the computer front panel to come on.
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