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Fuel Quantity Indicating System Component Location 5C8
28-41-05 Figure 1 (Sheet 1) Aug 01/96
Page 2
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
5C8 Fuel Quantity Indicating System Component Location
Aug 01/96 Figure 1 (Sheet 2) 28-41-05
Page 3
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
Fuel Quantity Indicating System Component Location 5C8
28-41-05 Figure 1 (Sheet 3) Oct 20/92
Page 4
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
2. Tank Units
A. The tank units are cylindrical capacitors which are mounted throughout each fuel tank to sense fuel level variations and, as a result of capacitance change, transmit electrical signals to the fuel quantity indicators (Fig. 1). The tank units consist of two coaxial cylinders which are rigidly spaced at intervals throughout their length by insulating centering spacers. The inner electrode is a variable diameter tube of electroformed nickel alloy and is connected to the amplifier input. The outer electrode is an aluminum alloy tube of constant diameter and is connected to an excitation voltage lead. The diameter of the inner electrode is profiled to provide an output signal which is linear with respect to the volume of fuel in the tank. Openings at the ends of tank units allow fuel to assume the same level between the two cylinders as that in the fuel tank. Tank units are located in the fuel tanks so that errors due to airplane attitude are kept to a minimum.
B. Tank units are mounted to main tank wing ribs and to center tank spanwise beams. Access to the tank units is obtained through fuel tank access openings. Electrical connections to tank units are made at the tank unit terminals (Fig. 1). Tank unit leads, within a given tank, form a harness which terminates at a receptacle (Fig. 2). The receptacles for tanks No. 1 and 2 are located in the respective wing front spar, and for the center tank in the main landing gear wheel well forward bulkhead on the left side. Mating with each receptacle is a bussing plug assembly. The plug assembly connects the tank units in parallel.
3. Compensator: Units
A. The compensator unit in each tank acts as a sensing element to maintain a linear relationship between fuel dielectric properties and fuel density. Each compensator unit consists of a low impedance plate and two high impedance plates, both protected by a mechanical shield. The compensators are mounted to the same wing structure as tank units and are located so that they are completely submerged in fuel at all times. Access to the compensator units is obtained through the fuel tank access openings. Leads from the compensator units are contained in the same harness used for the tank units.
5B8
Oct 20/85 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 28-41-05 Page 5
4. Fuel Quantity Indicators (Airplanes with digital indicators)
A. Precalibrated digital fuel quantity indicators on P2 panel show the weight of fuel in each tank. Each indicator consists of a single chip microcomputer system and a digital liquid crystal display (L.C.D). The microcomputer measures the capactive and resistive current in the tank units. The microcomputer also monitors the leakage current and other circuit parameters such as open circuits. When any parameter reaches an unacceptable level an error code is displayed on the indicator face. The display will read ERR plus an error code between 1 and 9 to be used to assist in trouble shooting the system. The following define the error codes.
ERROR FUEL QUANTITY FUELING QUANTITY CODE INDICATOR (P2 Panel) INDICATOR (P15 PANEL)
1 Excessive Leakage between HI-Z and NA
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