(e)
The video processor also adjusts the overall threshold attenuation and penetration compensation. This compensates for weakened radar returns to intervening targets. Also, the video processor determines the intensity of the weather target and stores this in the video memory. The timing and control circuits sends antenna tilt and scan angle data, selected range data, and any detected fault data to the video memory.
(f)
Receiver/Transmitter Antenna Stabilization Functions (Fig. 3)
EFFECTIVITY
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1) The antenna stabilization system is a microprocessor-controlled servo loop. The microprocessor receives inputs from: roll and pitch attitude, selected tilt angle, and elevation and azimuth scan angles of the antenna. The microprocessor solves the line-of-sight equation from these inputs and predicts the new position of the antenna elevation. The difference between the predicted position and the desired position is used to derive the elevation motor drive signal. The azimuth drive is an open-loop operation. For this, the microprocessor monitors the position of the antenna and generates signals to reverse the direction of scan when the antenna reaches 90 degrees either side of dead ahead.
(g) Receiver/Transmitter System Monitoring Functions (Fig. 3)
1) Control (setting the operating mode, range, tilt, etc.) and monitoring of operational status of the radar system is performed by a microprocessor-based system. During each microprocessor program loop, the 32-bit serial control word is checked to determine the selected mode of operation from the control panel and range selected on the indicator. The microprocessor then sends information on the data bus and control bus to set the system to the selected operating conditions. Additionally, during the program loop, selected inputs are checked or compared to determine the operational status of the system. The results of these checks or comparisons are used to control the display of fault warning messages on the indicator and to light annunciator LEDs on the front panel of the R/T unit. The fault annunciators on the front of the R/T unit are not illuminated unless the TEST pushbutton is pressed. Initially, when the TEST pushbutton is pressed (and held), all fault annunciators come on for 1 second to perform a lamp test; then they all go off if no fault is detected. If any of the fault annunciator LEDs stay illuminated, a failure in that unit is indicated. Releasing the pushbutton causes all annunciators to go off and remain off. The LED's and indicator faults are as follows: a) R/T - R/T fault b) ANT - Antenna fault c) CON - Control panel fault d) ATT - INS input fault e) IND - Indicator fault f) COOL - R/T cooling fault
2) The timing control and monitoring module in the R/T performs the system monitoring functions. The module has a timing and control (T&C) microprocessor, power supply monitor, discrete monitor, antenna stabilization, fault memory, data bus, receivers and decoders and various other circuits.
EFFECTIVITY
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3) Initially after power turn on the power supply monitor checks various dc voltage levels. The monitor also receives a temperature sensor input to detect an overheat condition in the receiver/transmitter mount cooling system. The timing and control microprocessor codes the fault condition and stores it in the fault memory.
4) During each R/T transmit/receive period of operation, the timing and control module checks the operation of the receiver/transmitter and antenna. The antenna stabilization and drive circuits stabilization processor performs software tests on its own circuits, antenna drive circuits, the antenna unit and inertial reference unit (IRU) inputs. Any fault conditions are sent from the antenna stabilization processor to the T&C microprocessor. The timing control microprocessor codes the fault condition and stores it in the fault memory.
5) Normal power supply voltages and temperature causes the timing microprocessor to enable the BITE circuit antenna stabilization micorprocessor. When a fault is detected the microprocessor goes through a fault routine to locate the fault condition. Faults are sent by a data bus to the timing microprocessor which codes the fault condition and stores it in the fault memory.
6) The BITE monitoring circuits in the timing control checks each of the weather radar unit functions to determine which replaceable unit or units are faulty. The BITE circuits generate fault messages which are sent through ARINC 453 data buses No. 1 and 2.
7) When a fault is detected the receiver/transmitter T&C microprocessor also stores the fault in the fault memory for display when the R/T front panel TEST switch is pressed.
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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3(98)
