A simple interface circuit to measure very small capacitance changes in capacitive sensors

This paper presents an easy to make interface circuit to measure very small percentage capacitance variations in capacitive sensors specially suitable for industrial measurements. A computer controlled 24 bit A/D converter is employed to obtain a higher resolution. This interface circuit can be used with any type of a capacitive sensor. The most interesting thing is that the accuracy of the measurement through this interface circuit is independent from the initial value of capacitance of the sensor. In addition, the double differential operating principle used here results in a minimum error due to coupling and stray capacitance of sensor probes