SELF CALIBRATED NON CONTACT CAPACITIVE TYPE LEVEL SENSOR FOR LIQUID AT DIFFERENT TEMPERATURES
A novel non contact, fringe capacitance based sensor is proposed to measure the liquid level in process industries, to avoid the effects of hazardous liquids chemicals. In practical situations, the sensors are required to be calibrated repetitively when the dielectric medium/dielectric constant changes owing to the fluctuations in the process/environmental parameters. This work deals with the design of low cost, noncontact, fringe capacitance based sensor for monitoring multi threshold levels employing self calibration feature. A sensor with Al electrodes is fabricated and interfaced with PLC S200 through switching unit. The performance is evaluated with same liquid at four different temperatures which leads to significant changes in dielectric constants. The results indicate that the concept of fringe capacitance facilitates the feature of self calibration. It is also observed that the PLC S200 monitors the existing threshold level with lowest error varying from 0.408% FSO to 0.816% FSO.