US Patent 8973612 Capacitive sensing electronic faucet including differential measurements

A fluid delivery device including an electronic faucet having a plurality of faucet components, and a primary capacitive sensor coupled to at least one of the faucet components and providing a primary output signal. At least one secondary capacitive sensor is located on or near an item which causes unintended effects on the output signal from the primary capacitive sensor and provides a secondary output signal. A controller determines a difference signal between the primary and secondary output signals of the primary and secondary capacitive sensors to control operation of the electronic faucet.