What is the primary function of the probe in a capacitance type fuel level gauge?

The primary function of the probe in a capacitance type fuel level gauge is to serve as a capacitor where fuel and air together act as one plate of the capacitor. In this setup, the presence of fuel alters the dielectric constant of the medium between the plates of the capacitor. This variation in the dielectric constant is directly related to the fuel level in the tank. As the fuel level rises or falls, the changes in capacitance are measured, allowing the gauge to determine how much fuel is present.

In capacitance fuel level systems, the accuracy of the measurement is significantly influenced by the dielectric properties of the materials involved, particularly the fuel, which has a different dielectric constant compared to air. This principle is crucial in designing efficient and accurate fuel level measurement systems in aircraft.