SH4

M19435
  GUN 201-999 ú

 31-31-00
 ú CONFIG 1 ú 01 Page 10 ú Jan 28/02

A

757
MAINTENANCE MANUAL

SH 1, 2 OR 3

Flight Data Recorder System Schematic
Figure 2 (Sheet 4)

 GUN 001-050, 052-999 ú

 31-31-00
 ú  CONFIG  1
 ú  01  Page 11
 ú  Sep 28/01 

M19457
A

757
MAINTENANCE MANUAL

 (2)  Parameter Inputs
 (a)  
The DFDAU receives inputs from sensors and signals from other airplane systems. The inputs are grouped as analog, discrete, and ARINC 429 digital inputs.

 (b)  
Accelerometer 1) The accelerometer receives 28-volt dc power from the DFDAU. 2) The unit consists of three independent accelerometers, one

 for each axis. Each accelerometer operates as a closed loop servo system that is responsive to linear acceleration along its sensitive axis. An applied acceleration results in a force on a seismic pendulum which disturbs the servos capacitive balanced bridge. As a result of this imbalance, the servo applies current to a torquer coil to return the pendulum to its original position. A sensing resistor in series with the torquer coil, provides a voltage that is proportional to the acceleration input. The voltage is then amplified and output to the DFDAU.

 (c)  
ARINC 429 DIT Inputs 1) The left and right engine EPR transmitters provide the EPR signals.

 2)  The left or right EICAS computer, via the EICAS select switch provides control surface signals. These signals are: a) Thrust Reverser In-Transit and Deployed b) Left and Right Aileron posiiton c) Left and Right Elevator Position d) Left and Right Rudder Position
 3) The left ADC provides altitude and airspeed signals. 4) The left or center EFIS symbol generator provides pitch and
 roll attitude and magnetic heading signals. 5) The left IRU provides longitude and latitude signals. 6) The captain's clock provides GMT signals.
 (3)  Digital Flight Data Acquisition Unit Function
 (a)  
The DFDAU receives 115v ac power from the FLIGHT RECORDER AC circuit breaker through either the manual or automatic switching circuits. The DFDAU contains a switching regulator power supply that generates the necessary internal voltages and provides excitation outputs as follows: 1) 28v dc for accelerometer excitation 2) 5v dc for potentiometer sensor excitation 3) Constant current sources for temperature probe excitation.

 (b)  
The DFDAU receives the flight parameters to be recorded. It processes and formats the signals. It then transmits the data to the DFDR for recording. Data acquisition, signal processing and output data streams are controlled by the central processing unit (CPU).
　
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