Texas Instruments Incorporated
SENSING FROST AND ICE ACCUMULATION USING CAPACITANCE

Abstract:

A capacitance sensing system senses frost and ice accumulation in an energy efficient defrost system. The capacitance sensing system comprises a first capacitor including a portion of a metal heat exchanger and a sensor electrode electrically isolated from the metal heat exchanger; a tank oscillator including a second capacitor and an inductor coupled in parallel with each other and with the first capacitor; and a circuit coupled to the tank oscillator. The circuit determines a resonant frequency of the tank oscillator, determines a capacitance value of the first capacitor based on the resonant frequency of the tank oscillator, and transmits a heater activation command in response to determining the capacitance value is greater than a threshold.