Design of a switching unit for fringe capacitance based smart sensor for multi threshold liquid level monitoring

The design of non-contact type sensor based on the concept of fringe capacitance and its performance evaluation infers that it employs self-compensation but restricts monitoring to a single threshold level. This is overcome by designing a multi threshold liquid level sensor with increased number of electrodes. This increases the complexity of Signal Conditioning Circuit (SCC) and also confines the resolution of measurement. The present work focuses on the development of a switching unit using a PLC. A comparative study of sensors having electrodes of different dimensions is also considered in this work. For experimental purpose, a PVC container of cylindrical geometry with 10 aluminium electrodes is fabricated. The programmed PLC-S100 accesses the data from multi electrode sensor through switching unit and SCC which determines the threshold level by monitoring the peak differential capacitance. The experimental results indicate that the switching unit developed here conveys the output of multi-electrode senor through the SCC and enables the PLC to identify the threshold levels with enhanced resolution.