Design of a multi electrode capacitance based liquid level sensor
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A capacitive liquid level Sensor implemented has been implemented in this project. Arrays of eight electrodes were used in place of a single electrode. The sensor is based on the fringing capacitance. The measurement was done using low cost capacitive-controlled oscillators. A PIC micro controller was used to compute the frequencies from the oscillators and perform the normalization and calibration of the liquid level. A change in capacitance causes a frequency shift in the oscillators. The shift in frequency has a direct relation to the change in capacitance which is a measure of the liquid level. The sensor can measure absolute levels up to 80mm with a resolution of 0.001 mm within a time of 10 seconds. One of the advantages of this liquid level sensor is that the data is acquired by a PC terminal using the serial port which facilitates online diagnosis of the liquid level, other advantages are of this sensor array response varies in the presence of mixtures of different liquids which helps on their detection. The sensor also works well in environments where the liquid is topped with a layer of froth. The proposed design was successfully built, calibrated and tested.