Which statement describes capacitive sensing in fuel gauges?

• A. Capacitance changes due to dielectric properties of fuel and air.
• B. Capacitance is unaffected by fuel grade.
• C. Voltage remains constant.
• D. Physical gauge movement.

Answer: (A)

Capacitive sensing works by measuring how the dielectric between sensor plates changes as fuel level varies. The capacitance depends on the dielectric constant of the material between the plates: air has a low εr, while fuel has a higher εr. As fuel level rises, more of the gap is filled with fuel (higher εr), so the capacitance increases. The fuel gauge electronics detect this change and translate it into a level reading. The idea that capacitance is unaffected by fuel grade isn’t accurate because different fuels can have different dielectric properties, which can affect calibration. Saying voltage stays constant describes another aspect of measurement, not the fundamental sensing principle, and a physical gauge movement refers to mechanical rather than capacitive sensing.