747-400 AMM 飞机维护手册导航 NAVIGATION 1(90)_航空信息_民用航空_通用航空

(3)
Data will be provided by the center ADC when it is used as an alternate source for either the left or right ADC.

11. Operation (Fig. 2)
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A. Functional Description
(1)
The left air data computing system is shown on the schematic and is covered in the following write-up. The center and right systems are similar, so the coverage for the left system applies.

(2)
Power is supplied to the left air data system from the 115v ac, 400 Hz standby bus. This power is rectified, filtered and regulated by the ADC power supply to output dc voltages. The ADC transformer converts the 115v ac to 26v ac. This stepdown voltage is applied through the L AOA circuit breaker to the ADC and the AOA sensor. It is used for reference and excitation voltage.

(3)
The ADCs use pneumatic and electric signals as input data. This data is converted to digital data for use by the central processing unit (CPU). The CPU controls all operations. It performs the required computations and outputs the proper data to the output transmitters. The CPU is represented by the compensation, computation, correction, and calculation circuits.

(4)
Pitot and static air pressures are applied to the ADC from the pitot-static system. The ADC uses two identical pressure sensors to convert the pressures to frequencies that are proportional to pressure. These frequencies are converted to digital data for use by the CPU. The data is calibrated and then corrected for static source error. Static source error is the ratio of pressure error to static pressure. Correction factors are stored in the CPU memory and used to make the required compensation.