Target material sensing using resonant circuit with sensing capacitor and electrical isolation

A refrigeration unit that comprises:

• a metal heat exchanger;
• a sensing capacitor having a sensing zone between two terminals of the capacitor, and arranged such that an amount of target material in the sensing zone changes a capacitance of the sensing capacitor;
• a resonant circuit including the sensing capacitor, wherein the metal heat exchanger is electrically isolated from at least part of the resonant circuit;
• a resonant circuit analyzer configured to detect a resonant frequency of the resonant circuit and to output a digitized analyzer signal based on the resonant frequency;
• a processor coupled to the resonant circuit analyzer, and configured to receive the digitized analyzer signal and to estimate an amount and a phase of the target material using a mathematical function or table responsive to the digitized analyzer signal;
• and
• a defrost unit configured to receive a control signal from the processor, wherein the control signal is in response to the estimate.

An apparatus that comprises:

• a sensing capacitor with two terminals and a sensing zone between the two terminals, wherein variance of a target material in the sensing zone changes a capacitance of the sensing capacitor,
• a metallic conduit to convey fluid;
• and
• at least one printed circuit board (PCB) comprising:
• a ground node;
• a sensing channel node;
• at least one LC component coupled to the sensing channel node to complete a resonant circuit that includes the sensing capacitor, wherein the metallic conduit is electrically isolated from the ground node and the sensing channel node;
• a resonant circuit analyzer configured to track a resonant frequency of the resonant circuit as a function of time and to output digitized analyzer signals based on the tracked resonant frequency as a function of time;
• and
• a processor coupled to the resonant circuit analyzer, and configured to receive the digitized analyzer values and to estimate an amount and a phase of a target material using a mathematical function or table responsive to the digitized analyzer values.