The research on high sensitivity and anti-saturation of capacitance sensors for measuring yarn evenness

Abstract

Yarn evenness is an important physical parameter of yarn quality. Capacitance sensors provide signals that are used to enable automatic measurement of yarn evenness. These capacitance sensors are expected to be extremely sensitive, highly linear, and electronically homogeneous. But, extremely sensitive sensors can saturate the circuit output under the influence of ambient temperature and humidity. Hence, 3D models of a cylindrical capacitance sensor and parallel plate capacitance sensor are constructed by using finite element analysis. Detection performance of the two types of sensors is compared in terms of sensor sensitivity, linearity, and evenness. We also propose a highly sensitive phase-sensitive detection circuit for the transformer bridge that converts capacitance into a voltage signal. In order to address the problem of premature saturation in the conditioning circuit, this paper proposes a compensation circuit that consists of a programmable capacitor to detect and compensate for output drift in the circuit in real time. Experimental results demonstrate the performance of the proposed capacitance sensor.