Proximity System Sensors
Figure 3

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 (4)  For sensor details and locations, refer to section of airplane subsystems listed in General paragraph.
 3.  Operation_________
 A. Functional Description (Fig. 4)
 (1)  
When the PSEU is powered by 28V dc, the sensor is driven by a periodic pulse generated in the PSEU prox card. This periodic pulse measures the inductance of the sensor. The sensor inductance increases as a steel (magnetic) target is brought near the face of the sensor. The sensor inductance decreases as the target is moved away from the sensor. When a specific inductance is measured, the output of the prox card changes state. This output is nominally 0.3V (logic 0) with a target near condition and approximately 13V (logic 1) with a target far condition.

 (2)  
The discrete mechanical switch outputs to the PSEU is a logic 0 with switch closure to ground, and a logic 1 with switch open or 28V dc. Table 1 lists the discrete inputs to the PSEU.

 ~.............................................................. | Table 1 | | Discrete Inputs to the PSEU | ................................................................ | PSEU Code | Input | ................................................................ | 421 | Landing gear lever up sys 1 | | 422 | Landing gear lever down sys 1 | | 423 | Landing gear lever down sys 2 | | 424 | Landing gear lever up sys 1 | | 425 | Gear truck positioner hydraulic pressure sys 1 | | 426 | Gear truck positioner hydraulic pressure sys 2 | 2...........…..................................................1

 (3)  
Both prox card output signals and the discrete switches output (gear truck positioner actuator hydraulic inlet pressure switches position, and gear lever position) signals apply directly to the logic card. The logic card circuit converts these inputs singly and in groups into output signals to the driver card. When the input signal to the driver card is a logic 1, the driver card provides a ground signal for operation of relays, lamps and other electronics. For description of sensor locations and logic circuit, refer to individual airplane subsystems section listed in 1.A.

 B.
PSEU Built-In-Test Equipment (BITE)

 (1)  
The PSEU BITE section is a microprocessor based system used to locate system faults. The BITE also provides ground test and automatic in-flight test.

 (2)  
The ground test mode contains three separate modes which provide a complete system check-out, a shortened subsystem check-out, or indication of sensor target near or far status.

 (3)  
On-ground BITE testing can only be activated when both main landing gear trucks are not tilted. Attempting to perform an on-ground BITE test with the airplane in the air mode will cause "AAA" to be displayed on the PSEU display and the test will not be performed.

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AIR/GND RELAYSDRIVER
LANDING GEAR POSITION AND WARNINGOUTPUTS R ENG THRUST REVERSER CONTROL
THRUST REVERSER INDICATION

FWD CARGO DOOR CONTROLDRIVER
AFT CARGO DOOR CONTROLOUTPUTS DOOR WARNING
THRUST REVERSER INDICATION

AIR/GND RELAYS
DRIVER LANDING GEAR POSITION AND WARNINGOUTPUTS L ENG THRUST REVERSER CONTROL PROXIMITY SWITCH ELEX UNIT (PSEU)
Proximity Switch System SchematicFigure 4 (Sheet 1)
M23046
DRIVER CARD (TYP 4 PLCS)

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