Digital Fuel Gauging Probe Multiplexer Architecture
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Solution Overview
Problem
Conventional aircraft fuel gauging systems with individual capacitance probes are complex, costly, and less reliable due to increased wiring and monitoring electronics, which complicates fuel level measurement and adds weight.
Innovation Solution
A fuel gauging system with addressable capacitive probes, a remote fuel computer unit, a densitometer, and a liquid dielectric constant sensor, utilizing a multiplexer and microcontroller to directly measure capacitance, temperature, and impedance, converting data into digital format for accurate fuel quantity calculation, and communicating it to the avionics computer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If individual capacitance probes are used for fuel measurement, then fuel level measurement is achieved, but system complexity and wiring requirements increase
Solution Approach 1:
Multiple capacitance probes are electrically connected in parallel to form a single combined probe assembly. This merging approach allows the system to measure fuel levels across multiple locations simultaneously while reducing wiring requirements and system complexity. The parallel connection enables shared signal processing electronics, eliminating the need for separate monitoring circuits for each individual probe.
Solution Approach 2:
The combined probe assembly serves multiple functions: it measures fuel levels at multiple locations, provides redundancy for reliability, and interfaces with a single set of electronics. The system can determine both local fuel levels at probe locations and overall fuel quantity in the tank, making the measurement system more versatile without proportionally increasing complexity.
2Measurement precision
If individual capacitance probes with separate monitoring electronics are used, then fuel measurement is achieved, but system weight increases
Solution Approach 1:
Multiple probes are combined into a single electrical assembly that shares common signal processing electronics, power supply circuits, and data processing pathways. This consolidation eliminates redundant electronic components and wiring that would otherwise add significant weight to the system, while maintaining the ability to accurately measure fuel quantity through the combined capacitance signals from all probe locations.
3Measurement precision
If multiple individual probes are used for comprehensive fuel measurement, then measurement coverage is improved, but reliability decreases
Solution Approach 1:
The parallel connection of multiple probes creates a redundant measurement system where the failure of individual probes does not cause complete system failure. The combined electrical assembly provides a unified signal path that can tolerate certain component failures, and the system can continue to provide fuel level measurements using the remaining functional probes, thereby improving overall reliability while maintaining comprehensive measurement coverage.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system provides accurate and reliable fuel measurement with reduced complexity, weight, and cost, enabling more economic flight operations by minimizing the need for additional fuel reserves.
Implementation Method 1
The level of the fuel within the probe alters the capacitance value of the probe. The capacitance of the probe varies linearly with the fuel level within the probe.
Implementation Method 2
a submerged fuel probe forming a capacitor with fuel as the dielectric
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
A fluid measurement system utilizes one or more digital probes that communicate over a digital bus to a fluid gauging computer. The digital probes incorporate a capacitance to digital circuit that converts probe capacitance to a digital value. The digital value is communicated to the fuel gauging computer via a data bus.