Design and development of level transmitter using capacitive sensor with wireless readout

Abstract

A simple, low cost level transmitter technique has been proposed in this paper. The capacitive level sensors are most commonly used for the measurement of liquid level in the industries because of their high sensitivity, less power dissipation and ruggedness in design. However, in a capacitance sensor, the problem of high nonlinear response characteristics as well as dependence on the permittivity of liquid have imposed some restriction on the optimal use of such sensors. In the proposed technique, the capacitance is measured from the cylindrical capacitive level sensor to the corresponding level of the liquid. The capacitance of the sensor related to the height of liquid level is converted into voltage signal with the help of a frequency to voltage converter. The frequency to voltage converter output is passed through signal conditioning circuit to meet the requirements of processing unit. In this study, the design of level transmitter with wireless readout has been described using cylindrical capacitive sensor as a primary sensing element and ATmega328 microcontroller unit for improving the linearity characteristics and wireless transmission. In this design, artificial neural network is used in cascaded with frequency to voltage converter, which is used along with a 555 timer IC for the conversion of capacitance into frequency. The voltage-level relation of the cylindrical capacitive sensor based level transducer exhibits a considerable nonlinearity. To estimate and compensate the nonlinearity of the level transmitter, we propose an artificial neural network (ANN). In the proposed transmitter, sensor is used to give the linear response over a wide range and is independent of liquid so that calibration of sensor is not required each time the liquid changes. The intelligence of ANN modelling is included into an embedded plug-in-module (PIM). The functionality of the transmitter has been tested experimentally. The proposed transmitter has exhibited considerably high sensitivity of about 37 mV/cm over the level range of 0-30 cm. The performance of the proposed transmitter is verified with recently reported techniques.