US Patent 9789697 Fluid level sensor with combined capacitance and conductance

A fluid sensor has a first electrode, a second electrode, a housing containing the first and second electrodes, such that the electrodes extend from the housing, exposed metal between the first and second electrodes, and a drive signal electrically connected to the second electrode, such that when fluid is present in the reservoir, either the first electrode senses the presence of the fluid, or the drive signal senses presence of the fluid. A fluid sensor has a first electrode, a second electrode, a housing containing the first and second electrodes, a drive signal electrically connected to the second electrode, and sensing circuitry to measure a current from the second electrode to indicate a fluid level.