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Flap/slat electronics unit (FSEU)
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Overhead panel ARINC 629 system (OPAS)
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Proximity sensor electronics unit (PSEU).
Discrete Outputs
The PA/CI controller controls software installation of the SDMs. The PA/CI controller sends a token discrete to the first SDM in a column during software installation.
The PA/CI controller sends a pause signal to the IFE system to pause the entertainment audio during an all area PA announcement.
CSMU Interface
The PA/CI controller and cabin system management unit (CSMU) use the intersystem bus for test and software installation data. They also share system data.
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PAS -PA/CI CONTROLLER FUNCTIONAL DESCRIPTION
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PAS -SDM AND ANS FUNCTIONAL DESCRIPTION
General
The speaker drive modules (SDMs) get digital audio from the PA/CI controller. They change the digital signal to analog and send it to one or two speakers.
The ambient noise sensors (ANSs) monitor cabin noise levels. They send a noise level signal to a SDM, which sends it to the PA/CI controller.
Speaker Drive Module
The PA/CI controller sends up to six channels of PA audio to the SDMs on an EIA-485 bus. The audio receiver and D/A converter change the digital signal to analog. Input to the D/A converter from the microprocessor includes data from the configuration database in nonvolatile memory (NVM). The configuration database gives the correct channel for each speaker.
Chime and volume data from the PA/CI controller go to the EIA-485 interface. The EIA-485 interface sends the data to the microprocessor.
When a chime condition occurs, the microprocessor sends a signal to the chime generator. The chime generator makes the correct type of chime sound and sends it to the sum module. The sum module mixes the signal with the audio for the applicable speaker. The sum module sends the audio to the level controller.
The microprocessor sends a signal to the volume controller to set the correct volume. The volume controller sets the volume for each speaker and sends the audio through an amplifier to the speaker.
The discrete interface gets a token discrete during the software installation process. After the software is installed, the microprocessor sends the discrete to the next SDM.
Ambient Noise Sensors
Some SDMs connect to an ANS. The SDM sends power to the ANS. The ANS uses the voltage to power a microphone. The microphone changes the acoustic noise into an electrical signal and sends it to a filter. The filter passes frequencies only in the audio range. The filter sends the signal to a RMS converter. The RMS converter changes the AC signal to a DC signal. The DC signal is in proportion to the cabin noise level. The ANS sends the signal to the SDM.
The SDM changes the DC signal to digital format and sends it to the PA/CI controller through the EIA-485 interface. The PA/CI controller uses the data to calculate the correct volume levels throughout the cabin.
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777 AIRCRAFT MAINTENANCE MANUAL
PAS -SDM AND ANS FUNCTIONAL DESCRIPTION
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PAS -PASSENGER ADDRESS CONTROL SCREEN
General
The passenger address screen permits you to adjust the PA volume. It also permits you to disable the ambient noise sensors (ANS).
You can access the screen on the CSCP or on any CACP.
Access
Touch PASSENGER ADDRESS on the cabin controls main menu screen to show the passenger address screen.
Volume Control
Touch the area selection arrows to select an area.
The configuration database identifies the airborne volume reference level. The volume indication shows the current volume above the reference level. Green vertical bars show the volume for the area selected.
The STEPS ABOVE MINIMUM shows the number of increments above the reference level. The range is from 0 to 16. The configuration data base determines the amount each increment increases the volume.
To increase the volume, touch the right arrow. To lower the volume, touch the left arrow. You cannot lower the volume level below the reference level.
Touch AREA RESET to return the volume to the reference level.
Ambient Noise Sensor Control
The ANS section permits you to enable or disable the ANSs. The ANS control goes to all ANSs in the airplane.
Touch ON to enable the ANSs. The PAS uses ANS inputs to calculate the volume levels.
Touch OFF to disable the ANSs. The PAS uses flight inputs to calculate the volume.
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