Method and system for sensing a liquid level

A system for sensing liquid level in a receptacle, said system comprising:

• a capacitive sensing probe for sensing a capacitance between the capacitive sensing probe and an electrically conductive portion of the receptacle;
• a control circuit connected to the capacitive sensing probe for detecting a level of the liquid in the receptacle based on said capacitance;
• a non-isolated AC power supply arranged to power the control circuit, the non-isolated AC power supply having an electrical connection between its input and its output;
• and
• at least one filter capacitor (C1, C2) connected in series between the capacitive sensing probe and the control circuit, wherein the control circuit is arranged to receive an AC voltage from a mains supply and convert the AC voltage into a zero-crossing signal used to trigger the capacitive sensing, and wherein the capacitive sensing is triggered with a time delay after a zero-crossing point of zero-crossing signal is detected, the time delay is a pre-determined value or range.

A system for sensing liquid level in a receptacle, said system comprising:

• a capacitive sensing probe for sensing a capacitance between the capacitive sensing probe and an electrically conductive portion of the receptacle;
• a control circuit connected to the capacitive sensing probe for detecting a level of the liquid in the receptacle based on said capacitance;
• a non-isolated AC power supply arranged to power the control circuit, the non-isolated AC power supply having an electrical connection between its input and its output;
• and
• at least one filter capacitor (C1, C2) connected in series between the capacitive sensing probe and the control circuit, wherein the control circuit is arranged to detect whether an edge of the zero-crossing signal is a rising edge or a falling edge, and the control circuit is arranged to detect the level of the liquid in the receptacle based on the capacitance of the capacitive sensing probe based on results of the detection.