Fuel Quantity Test Sets are self-contained, universal test sets for testing aircraft fuel quantity systems and components. They are designed to calibrate and troubleshoot both AC and DC capacitive fuel systems and help to isolate problems with fuel system wiring, circuits or components. Some models can also test capacitive components on oil, water, or LOX systems.
They can accurately measure fuel system insulation resistance and probe capacitance and can simulate capacitance and current needed to test the entire fuel system. Fuel Quantity Test Sets are used extensively by maintenance shops around the world to service all types of aircraft for both commercial and military use.
Fuel Quantity Test Set Capabilities
Aircraft fuel systems operate due to the change in the capacitance of the fuel probe as the fuel level increases or decreases and air replaces the fuel in the tank. A signal conditioner measures this change in capacitance and sends the reading to the fuel indicator in the cockpit. In most cases, the change in capacitance is very small, under 50 picofarads so the wiring and fuel system components must be able to perform very accurately.
To perform the various aircraft fuel system tests, Fuel Quantity Test Sets contain:
A microamp current output to check a variety of analog or digital current indicators.
A low-voltage Megohmmeter to measure the insulation resistance of wiring, probes or other system components.
A capacitance simulator to output accurate capacitance values to represent empty or full fuel tank conditions.
A capacitance bridge to measure the capacitance of individual fuel probes and interconnecting wiring.
An internal battery to make them portable for ease when working in or around the aircraft.
Fuel Quantity Test Sets also contain either special adapter modules or test cable harnesses for each specific aircraft type to connect the test set can be in-line with the signal conditioner and the probe system to make the appropriate measurements and adjustments.
Fuel System Tests
Several types of tests are performed on an aircraft’s fuel system using Fuel Quantity Test Sets. These tests are to be performed for each main tank and each set of auxiliary tanks on the aircraft.
This test is performed to verify the insulation integrity of the fuel system wiring. This test checks the resistance between the various wiring configurations to the fuel probes to ensure the proper separation of the wiring and aircraft ground. Most manufacturer’s specifications require a minimum of 1000 megohms resistance on the wiring to the probes and ground.
This test uses the Fuel Quantity Test Set’s capacitance bridge to measure the capacitance of the fuel probes and associated wiring to ensure they are within the proper manufacturer’s specifications. This test is performed after the tanks are drained and are empty.
This test simulates the capacitance of the fuel probes to adjust the proper empty and full fuel settings on the signal conditioners. These adjustments interact with each other and the capacitance simulation allows the technician to easily alternate between the empty and full fuel tank conditions to adjust the signal conditioner until both readings are correct. This test is also performed with empty fuel tanks and the adapter harness from the test set is connected to the signal conditioners for these adjustments.
Fuel Quantity Test Set Calibration
The functions that the Fuel Quantity Test Set performs on an aircraft are highly critical and the test set needs to be properly calibrated to ensure that the measurements and outputs are within the manufacturer’s design specifications.
The current output of the test set is calibrated by comparing the microamp output with a Digital Multimeter. The capacitance simulator is calibrated by comparing the capacitance output with a highly accurate RLC meter or capacitance bridge.
The insulation meter and capacitance bridge are calibrated by simulating various values by using high accuracy resistance and capacitance standards.
The calibration of Fuel Quantity Test Sets should be performed by a calibration laboratory that has the proper measurement standards and has technicians that have been extensively trained on their use.
has the appropriate calibration standards and expertise to accurately calibrate Fuel Quantity Test Sets and many other types of testing and ground support equipment used for aircraft maintenance. For more information on our calibration and testing capabilities, contact e2b calibration.
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