28-41-00
FUEL QUANTITY INDICATORS ú ú 01A Page 4 ú Nov 15/92
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
FUEL MEASURING STICK (IN TANK ACCESS DOORS NO. 1,4,6,8 AND 10)
SEE I
NO. 1 TANK SHOWN (NO. 2 TANK OPPOSITE)
FLAPPERCALIBRATED ROD VALVE
SLEEVE
SPRING BODY
RETAINING
SCREW
BAYONET
TANK ACCESS
DOOR SEE J LOCKING
PIN
CALIBRATION
DRIP PLANE
HOLE
FUEL MEASURING STICK (EXAMPLE) FUEL MEASURING STICK (EXAMPLE)
IJ
Fuel Quantity Indicating System Component Location
Figure 1 (Sheet 4)
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH ANALOG ú
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FUEL QUANTITY INDICATORS ú ú 01A Page 5 ú Nov 15/92
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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. When the capacitance in the tank units changes, electrical signals are transmitted to the fuel quantity indicators. A tank unit has two coaxial cylinders which are rigidly spaced at intervals throughout their length by insulated centering spacers. The inner cylinder (electrode) is a variable-diameter nickel-alloy tube and is connected to the amplifier input. The outer cylinder (electrode) is an aluminum-alloy tube of constant diameter and is connected to the excitation voltage lead. The diameter of the inner cylinder is profiled to supply an output signal which is linear with respect to the volume of the fuel in the fuel tank. Openings at the ends of the tank unit let fuel assume the same level between the inner and outer cylinder as the level 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 attached to wing ribs in the No. 1 and No. 2 tanks and to spanwise beams in the center tank. Access to the tank units is through access openings in the fuel tanks. 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 receptacle for No. 1 or No. 2 tank is found in the applicable wing front spar. The receptacle for the center tank is found on the forward bulkhead in the wheel well for the left main landing gear. The receptacle penetrates the tank spar and connects with a bussing plug assembly. The bussing plug connects the tank units in parallel.
3. Compensator Unit (Fig. 1)
________________
A. A 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 cylindrical plate and two high-impedance cylindrical plates, which are protected by a mechanical shield. The compensator units are attached to the same wing structure as the tank units. The compensator units are installed so they are completely submerged in fuel at all times. Access to the compensator units is through the access openings in the fuel tanks. The electrical leads from the compensator units are contained in the same harness used for the tank units.
4. Fuel Quantity Indicator (Fig. 1)
_______________________
A. The fuel quantity indicators show the weight of fuel in the fuel tanks. Each fuel quantity indicator has the reference side of a self-balancing capacitance bridge, a power transformer, an amplifier, a reversible two-phase induction motor, gear trains, pointers, a main dial, and a vernier dial. All fuel quantity indicators are hermetically sealed. An electrical connector and full and empty adjustment screws are at the rear of each fuel quantity indicator.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH ANALOG ú
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FUEL QUANTITY INDICATORS ú ú 01A Page 6 ú Jul 15/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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