Fuel gauge

As used in vehicles, the gauge consists of two parts: The sending unit usually uses a float connected to a potentiometer, typically printed ink design in a modern automobile.

As the tank empties, the float drops and slides a moving contact along the resistor, increasing its resistance.

An electric current is sent through the variable resistor to which a float is connected, so that the value of resistance depends on the fuel level.

These resistance sensors are also showing an increased failure rate with the incremental additions of alcohol in automotive gasoline fuel.

[5][8] Magnetoresistance type fuel level sensors, now becoming common in small aircraft applications, offer a potential alternative for automotive use.

Magneto resistive sensors are suitable for all fuel or fluid combinations, including LPG and LNG.

An aircraft may use a number (around 30 on an A320) of low voltage tubular capacitor probes where the fuel becomes the dielectric.

In early designs, the profiles and values of individual probes were chosen to compensate for fuel tank shape and aircraft pitch and roll attitudes.