(2)
Operation When an electrical current goes through the thermistor, its temperature increases. The electrical resistance of the thermistor changes with its temperature. When the sensor is in the fuel, the temperature increase is less than when the sensor is in the air. The FLSCU compares the current value from the sensor to a specified value to find if the related sensor is wet or dry.
R **ON A/C 001-049, 051-099, 101-149, 151-199, 201-299, 401-499,
B. Temperature Sensors 29QJ1(29QJ2), 30QJ1(30QJ2)
**ON A/C 301-399,
B. Temperature Sensor 29QJ1(29QJ2)
**ON A/C ALL
(1) Description (Ref. Fig. 007) The temperature sensor is a moulded probe with a triangular mounting flange. A platinum-wire resistor is installed in the probe. Holes in the probe let the fuel flow close to the resistor.
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Level or Temperature Sensor (Example)
Figure 007
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The temperature sensor has captive-screw connections that connect to ring-lug terminals. The sensor contains a fast-blow fuse. The fuse will prevent possible dangerous electric currents in the aircraft wiring. The sensor assembly is installed on a wing rib. The resistance value of the sensor is 1000 ohms at 0 deg. C.
(2) Operation The electrical resistance of the temperature sensor is in relation to the temperature of the adjacent fuel. When the temperature of the fuel, as calculated by the FLSCU, is at a specfied level the FLSCU stops the recirculation system (Ref. 28-16-00).
C. Fuel Level Sensing Control Unit (FLSCU) (7QJ,9QJ) (Ref. Fig. 008)
The FLSCU has:
-two circuit card assemblies
-
a chassis
-
a front plate
-an electronic module assembly. The circuit cards are located in the chassis by integral rails. The front plate closes one end of the chassis, the electronic control module closes the other end. The electronic module assembly has a mother board assembly and a rear plate. The mother board assembly has two connectors that connect to the circuit card assemblies. The rear plate has a connector that has an upper and a lower part, the connector is the units interface with its rack in the avionics bay. The mother board assembly controls all the inputs and outputs to and from the circuit card assemblies and the unit. The rear plate has three keying posts to make sure that the unit is installed correctly in the rack. Holes in the top and the bottom of the chassis let air flow through the unit to cool the internal components. The FLSCU has these functions:
-
a current supply, kept to a limit of safe values, for each sensor
-
a detection circuit to find when a sensing thermistor is in fuel
-
a switch comparator which has relay-contact output-signals and logic output-signals
-
a fault monitoring circuit that continously monitors for an open circuit or short circuit sensor (or sensor line) (and moves the output relay to the fail safe state)
-Built In Test Equipment (BITE), controlled and monitored by the FQI computer, to do a test of the fuel system sensors.
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Fuel Level Sensing Control Unit - Detail
Figure 008
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7. Operation/Control and Indicating
________________________________
The tank level sensing system operates automatically. When a sensor is in the fuel it is wet and when it is not in the fuel it is dry. When a sensor becomes wet or dry it changes its signal to the FLSCU.
A. High level Sensing
(Ref. Fig. 002)
The high level sensors, 17QJ1(17QJ2) and 20QJ, control the high fuel level in each tank during refuel or a fuel transfer. When the high level sensor becomes wet, the FLSCU closes the related inlet valve. During a refuel, the FLSCU also causes the applicable HI LVL light (3QJ, 4QJ and 5QJ) to come on at the refuel/defuel control panel 800VU.
R **ON A/C 001-049, 051-099, 101-149, 151-199, 201-299, 401-499,
B. Lo-level Sensing (Ref. Fig. 003) When the center-tank low-level-sensor 21QJ, 22QJ is dry for more than five minutes, the related center-tank pump will stop. If, during the five minutes, the sensor becomes wet, for a minimium of 11 seconds, the center-tank pump will continue to operate. Each center-tank pump will operate until the sensor continues to be dry for five more minutes. When the LH wing low-level sensors 15QJ1 and 39QJ1 or 16QJ1 are dry for 30 seconds continuously, a 750KG (1650 lb) LO LEVEL warning message is shown on the ECAM display unit. When the RH wing low-level sensors 15QJ2 and 39QJ2 or 16QJ2 are dry for 30 seconds continuously, a 750KG (1650 lb) LO LEVEL warning message is shown on the ECAM display unit.
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