Capacitive level sensor and control system

Abstract

A capacitive level detection system provides a highly accurate determination of liquid level within a container. The primary sensor is an elongate capacitive probe positioned vertically within the container so that a lower portion of the probe is in liquid and an upper portion of the probe extends above the surface of the liquid. A capacitive liquid reference sensor is proximate the lower end of the probe, and a capacitive gas reference sensor is proximate the upper end of the probe. A controller is provided for driving each of the sensors with an electrical signal and reading a resultant value corresponding to the capacitance of each of the sensors. The controller is configured to enable the system to be calibrated prior to installation by placing each of the sensors in a calibration or identical medium, reading sensor values corresponding to capacitances for each of the sensors, and calculating and storing calibration values based on the sensor values. Following installation, values read from each of the sensors are mathematically combined with the stored calibration values to determine liquid level within the container. Liquid level setpoints can also be programmed into the controller by a user to control liquid level within the container.