(20)
The end terminals of the tank wiring harness at the tank units or compensators can be repaired by replacement of the end terminals. All other damage to the tank wiring harness will result in replacement of the tank wiring harness.
(21)
Any corrosion or damage to the airplane wiring harness or the tank wiring harness can result in nuisance fault codes and nuisance status codes.
FILLET SEAL
HI-Z Bussing Plug
Figure 12
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MAINTENANCE MANUAL
(22)
Any damage to the connector pins at the FQPU connector, HI-Z bussing plug, or LO-Z connector plug can result in nuisance fault codes and nuisance status codes.
(23)
The tank wiring harnesses must be carefully installed and secured. An improperly installed, loose, or damaged tank wiring harness can introduce stray capacitance which would affect system accuracy.
(24)
Improper installation of a tank wiring harness can result in nuisance fault codes and nuisance status codes. For instance, a poorly secured connection of the tank wiring harness to the LO-Z, HI-Z shield, and HI-Z terminals of a tank unit or compensator can result in nuisance fault codes and nuisance status codes.
3. Operation (Fig. 13)
_________
A. Functional Description
______________________
(1)
Fuel Quantity Processor Unit (FQPU) Operation
(a)
The FQPU operates whenever the system receives power. No flight crew operator actions are necessary for the FQPU to compute and display fuel quantity.
(b)
Power requirements for the FQPU, 28 volt dc, normally comes from the battery bus, and the right main bus. Alternate power sources for the FQPU comes from the ground handling bus and the hot battery bus.
(c)
The battery bus normally supplies power to power supply 1 in the FQPU, and the right main bus supplies power to power supply 2.
(d)
The FQPU will operate even with only one power source available.
(e)
If a wiring fault exists for 73 seconds or more, the fuel quantity indicator will blank and the EICAS message, FUEL QTY IND, will show. If a wiring fault exists for less than 73 seconds, the fuel quantity indicator will not blank and the EICAS message, FUEL QTY IND, will not show. This is to prevent intermittent wiring faults from affecting in-flight fuel quantity indications. For maintenance purposes, any wiring fault detected, even those lasting less than 73 seconds, will be recorded by the FQPU and accompanied by the EICAS message, FUEL QTY BITE.
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