737-300/400/500MAINTENANCE MANUAL
CENTER TANKTANK UNITS
(EXAMPLE) SEE H
COMPENSATOR UNITS (1 EACH TANK)
SEE H
NO. 1 TANK SHOWN
(NO. 2 TANK OPPOSITE)
ELECTRICAL
TERMINAL
UPPER WING
SKIN
FWD
COMPENSATOR UNIT
LOWER WING SKIN TANK UNIT
H
Fuel Quantity Indicating System Component Location
Figure 1 (Sheet 3)
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A
737-300/400/500
MAINTENANCE MANUAL
FUEL MEASURING STICK (IN TANK ACCESS DOORS NO. 1,4,6,8 AND 10)
SEE I
NO. 2 TANK SHOWN (NO. 1 TANK OPPOSITE)
CALIBRATED ROD FLAPPER VALVE
SLEEVE
SPRING
BODY
RETAINING
SCREW
BAYONET
LOCKING PIN
SEE J DRIP HOLE
TANK ACCESS DOOR
CALIBRATION PLANE
FUEL MEASURING STICK (EXAMPLE)
I
FUEL MEASURING STICK (EXAMPLE) J
Fuel Quantity Indicating System Component Location
Figure 1 (Sheet 4)
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A 737-300/400/500MAINTENANCE MANUAL
2. Tank Unit (Fig. 1)
_________
A. The tank units are cylindrical capacitors which are installed throughout each fuel tank to sense fuel level variations and, as a result of capacitance change, transmit electrical signals to the fuel quantity indicators. The tank units have two coaxial cylinders which are rigidly spaced at intervals throughout their length by insulating centering spacers. The inner electrode is a variable diameter nickel alloy tube and is connected to the amplifier input. The outer electrode is an aluminum alloy tube of constant diameter and is connected to the excitation voltage lead. The diameter of the inner electrode is profiled to supply an output signal which is linear with respect to the volume of fuel in the fuel tank. Openings at the ends of tank units let fuel assume the same level between the two cylinders as that in the fuel tank.
B. Changes in airplane attitude can cause errors in the fuel quantity measurement. The tank units are installed in locations in the fuel tank that keep these errors to a minimum. The large number of tank units in different locations in the fuel tank also keeps these errors to a minimum.
C. Tank units are installed on the wing ribs in the No. 1 and No. 2 tanks and to the spanwise beams in the center tank. Access to the tank units is through fuel tank access openings. Electrical connections to the tank units are made at the tank unit terminals. Tank unit leads in a given tank, form a harness which terminates at a receptacle. The receptacles for the No. 1 and No. 2 tanks are found in the applicable wing front spar, and for the center tank in the left forward bulkhead in the wheel well for the main landing gear. Attached to each receptacle is a bussing plug assembly. The plug assembly connects the tank units in parallel.
3. Compensator Unit (Fig. 1)
________________
A. The compensator unit in each fuel tank acts as a sensing element to maintain a linear relationship between fuel dielectric properties and fuel density. Each compensator unit has a low impedance plate and two high impedance plates, which are protected by a mechanical shield. The compensators are attached to the same wing structure as tank units and are installed so that they are completely submerged in fuel at all times. Access to the compensator units is through the fuel tank access openings. Leads from the compensator units are contained in the same harness used for the tank units.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH SIMMONDS DIGITAL FUEL ú
28-41-02
QUANTITY INDICATORS ú ú 01 Page 6 ú Jul 15/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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