Predictive Windshear Central Processor Unit

The PWS CPU uses inputs from these systems to turn on the WXR PWS function:

· Auto throttle switch packs

· Radio altimeters.

 

The PWS CPU controls the antenna scan and pulse repetition frequency of the transmitter to detect windshear events directly in front of the airplane. The area is limited to a very small range because of the high pulse repetition frequency.

When the PWS CPU detects a windshear, it sends the warning or caution to the GPWS. The GPWS has the priority logic for warnings and cautions. If there is no higher priority warning or caution, the PWS CPU sends the windshear display to the DEUs and sends the aural signal to the REU. Also, the PWS CPU sends an aural inhibit to the TCAS computer to inhibit any aural signals from TCAS.

Oscillator/Transmitter Circuits

The oscillator/transmitter circuit makes RF pulse patterns and sends them out through the WXR antenna.

RF Transmit

 

The RF pulses go from the transmitter circuits through the circulator. The circulator connects the antenna to the transmitter during RF transmission. It also connects the

antenna to the receiver circuits to get the return RF pulses.

From the circulator, the RF goes to the WXR antenna.

RF Receive

The antenna receives the RF return signals. Then the RF goes through the circulator to the receiver circuits. The receiver circuits process the return signals and send them to the CPU. The CPU uses the strength of the RF return signals to calculate the intensity of the precipitation and to make the WXR display data.

When the PWS is on, the return signals may also contain windshear information. The PWS CPU processes the windshear returns and makes the aural signals and display signals.

WXR Display Data

The CPU puts this data into the ARINC 453 format:

· WXR display data

· Range processed

· System mode

· Status data.

 

The CPU sends the output data to the ARINC 453 transmitters. The 453 transmitters send the data on the high speed ARINC 453 DATA BUS 1 and DATA BUS 2 to the DEUs.

System Status Data

The BITE module continuously gets system status data. The system status and the faults show on the ND alert lines.

 

 

WXR SYSTEM - ANTENNA FUNCTIONAL DESCRIPTION

Antenna Control

The CPU in the WXR R/T controls and monitors the antenna operation.

Antenna Stabilization

The WXR R/T uses attitude inputs from the ADIRU for antenna stabilization. The CPU uses the attitude inputs to calculate and control the scan and elevation movements. It sends the scan and elevation drive signals to the antenna.

Antenna Operation

The antenna power supply gets 115v ac from the WXR R/T. The antenna power supply sends 26v dc power to the antenna motor driver. The motor driver sends 26v dc power to the scan and elevation stepper motors. The motor driver also sends power to the antenna position monitors.

Antenna Drive

The antenna has one scan motor and one elevation motor.The scan motor drives a geartrain which moves the antenna horizontally. It moves the antenna 90 degrees from the centerline of the airplane. The elevation motor drives a gear train which moves the antenna vertically. It moves the antenna up and down |40 degrees. This elevation range includes 15 degrees for the manual tilt.

Antenna Position Feedback

There are two zero and two incremental monitors in the antenna assembly. Each stepper motor has one zero monitor and one incremental monitor. The zero monitors read the zero or center position of the stepper motor. The incremental monitors count the number of steps the motor moves from the center position. The monitors send antenna position data to the WXR R/T.

Antenna Position Compare

The WXR R/T CPU uses the position information from the

monitors to compare the actual antenna position with the

desired antenna position. When the two are not the same, the WXR R/T sets the antenna fault.

Disable Switches

The disable switches are on the antenna pedestal. The scan disable switch disconnects the scan motor from the motor drive. The elevation disable switch disconnects the elevation motor from the motor drive. Because the motors disconnect from the motor drives, the antenna does not move.

CAUTION: AN OPEN DISABLE SWITCH DOES NOT STOP RF TRANSMISSION FROM THE ANTENNA.