Monitoring of Internal Power Supplies
Figure 011
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E. Monitoring of Sensors (Ref. Fig. 012) The analog inputs serve for the acquisition of 400 Hz signals of LVDT and RVDT sensors (these sensors give the position feedback of the yaw damper, rudder trim and RTL actuators). Each sensor delivers two analog voltages V1 and V2. The principle of the sensor is such that the ratio VX V1 - V2 -- = -------VR V1 + V2
is proportional to the position X of the actuator.
The voltage VR is proportional to the supply voltage of the 26V sensor.
The ratio VX/VR is always strictly inferior to value 1 in normal
operation. Each channel integrates a software monitoring which compares
VX/VR to a theoretical value function of the type of sensor (LVDT or
RVDT). This monitoring function therefore detects the cutoff of wiring
inside and outside the sensor. It serves to eliminate the channel related
to this sensor.
(Ref. Fig. 013)
A 26V compensation is introduced by a comparison in the software between
value VR (V1 + V2) and the theoretical VR value obtained for a nominal
26V/400 Hz.
For a difference lower than 25 %, a compensation value is added.
For a difference greater than 25 %, a logic of behaviour under short
cutoffs is used (Ref. 22-67-00).
This logic ensures:
-
For short cutoffs (less than 200 ms) : the inhibition of the system without disconnection
-
For long cutoffs : the disconnection of the system. A specific software has been implemented in order to detect any jamming of rudder position transducer unit.
F. Safety Tests
(1) General These tests permit to check the correct operation of the digital section and safety devices. These tests are activated on the ground (nosewheel shock absorber compressed and both engines shut down) after power cut-off greater than 4 seconds. Hardware inhibitions are provided (nosewheel signals to avoid any untimely activation in flight). These tests are automatic and last for 1 mn approximately. They are initiated in sequence in the command and monitoring channels. All the sequences must be present to validate the final result and enable the engagement of the system and functions. The test results are stored in non-volatile EEPROM and used in:
-The global logic of the FAC (common part test)
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Sensors - Principle
Figure 012
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26V/400 Hz Monitoring
Figure 013
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-The logic specific to the function (yaw, rudder trim, rudder travel).
(2)
General organisation These tests check:
-
The digital section
-
The synchronization between command and monitoring channels
-the safety hardware devices (hard-wired logic, watchdog, etc.)
(3)
Components tested These tests deal with:
-
The memory module (recognition of the memory modules and acknowledgement of their consistency with the computer and the expected software version)
-
The CPU RAM (bit-by-bit test of data and addresses)
-
The ARINC RAM (same as above)
-
The ARINC EEPROM (test of ARINC label conformity)
-
The watchdog (tripping)
-Power monitoring (activation)
-
The FAC HEALTHY signals (FAC internal monitoring)
-
The engage hard-wired logics of the yaw, rudder trim and RTL systems
-
The return-to-low speed logic of the rudder travel limitation unit
-
The memory module (OBRM): soft identification, checksum
-
The pin programming with parity check (odd parity).
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______________________________________________________________
1. General_______ The Flight Augmentation Computer (FAC) is a 8MCU size case. Its dimensions conform to ARINC Characteristic 600. The FAC is of modular design. The computer design is based on digital and analog technologies.
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