(2)
If the two LEDs are off, the fuel level is above the single point sensor.
F.
The two sensors are identified as channel 1 (CH1) and channel 2 (CH2).
CH1 agrees with the single-point sensor, probe F117 (SSM 28-44-01).
CH2 agrees with the single-point sensor, probe F119 (SSM 28-44-01).
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MAINTENANCE MANUAL
ELECTROSTATIC GROUND JACK
FUEL SYSTEM CARD FILE
SEE A
A
A
FUEL SYSTEM CARD FILE A
CARD A4A-A
Fuel Jettison Single Point Sensor Control Card Figure 501
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G. The single-point sensor control card includes several test functions to check the operation of CH1 and CH2. The test functions includes these components:
(1)
A CH1 and CH2 LED. The LED is "on" and the color is green when the fuel level is below the single point sensors in the No. 2 and 3 main tanks (the sensor is dry). The LED is "off" if the fuel level is above the single point sensors (the sensor is wet). The circuit is considered opened when the sensors are wet (LED is off) and grounded when the sensors are dry (LED is on).
(2)
A CH1 and CH2 BIT switch. The three position (center off) toggle switch on the SPS card allows for a check of the SPS control card logic.
(a)
If the fuel level is above the sensors (SPS wet - approximately 10-12 pF) and the CH1 or CH2 BIT is activated, a low fuel level is simulated. After approximately four seconds, the output changes state (becomes grounded) and the BIT LED comes on.
(b)
If the fuel level is below the sensors (SPS dry - approximately 3.5-9.0 pF) and the CH1 or CH2 BIT function is activated, the output changes state immediately and the BIT LED goes off.
(c)
If the SPS capacitance is out of range (below 3.5 Pf or above
12.1 Pf), the card output will be open circuited. The LED will be in the off condition. When the BIT switch is held in the applicable CH1 or CH2 position, the output will not change states. The LED will remain off.
(3)
A CH1 and CH2 FAIL SAFE TEST switch. The three position (center off) toggle switch on the SPS control card permits a check of the SPS fail safe circuit.
(a)
The control card is considered failed when one or more of these conditions exists: 1) An internal SPS control card problem which would change the
output signal 2) Loss of external 28 VDC power 3) Loss of a sensor CH1 or CH2 signal.
(b)
To test the fail safe circuit for a wet sensor (output open) you must: 1) Put the BIT switch to the CH1 or CH2 position and, 2) at the same time put the FAIL SAFE TEST switch to the
applicable CH1 or CH2 position.
NOTE: The LED light will go out.
____
(c) To test the fail safe circuit for a dry sensor (output grounded) you must: 1) Put the the FAIL SAFE TEST switch to the CH1 or CH2
position.
NOTE: The LED light will go out.
____
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TASK 28-31-17-705-001
2. Fuel Jettison Single Point Sensor (SPS) Control Card Operational Test_____________________________________________________________________
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