An oscillator based circuit for interfacing imperfect capacitive sensors

Abstract

Capacitive sensors are being used in various applications of sensing because of many attractive features such as high sensitivity, low power consumption, low temperature dependence and small size. However, these features are overshadowed by leaky nature of a capacitive sensor and also presence of large offset and parasitic capacitances reduce the measurement range and accuracy. A simple relaxation oscillator-based interfacing circuit has been proposed for separately measuring the capacitance and resistance change in-terms of frequency change of the oscillator output signal. The circuit has been successfully simulated and then implemented on breadboarded to represent both the capacitance and resistance in terms of frequencies. It shows the measurement range of the capacitance value 1 pF to 3.6 nF and the resistance range of 100 kΩ to 1.4 MΩ. The sensitivity of frequency output for low capacitance measurement is 9.98 Hz/pF.