MOE Key Laboratory of Fundamental, Physical Quantities Measurement, Hubei Key Laboratory of Gravitation and Quantum Physics, PGMF and School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China.
Scientific and Technological Innovation Center, Beijing 100020, China.
Rev Sci Instrum. 2022 Aug 1;93(8):085007. doi: 10.1063/5.0087555.
Area-changed capacitive displacement transducers (CDTs) are widely used in the high-precision displacement measurement due to their high accuracy and large dynamic range. The preamplifier circuit is used to convert the capacitance variation signal into voltage, which requires low noise and is significant for the high-sensitivity area-changed CDTs. Current CDT preamplifiers are mainly categorized as the low-impedance preamplifier and the high-impedance preamplifier; however, their characteristics and application scopes have not been systematically compared. This paper builds comprehensive models of the low-impedance and the high-impedance preamplifiers. Then, three-electrode configurations with different electrode separations and gaps are designed to carry out displacement variation experiments with low-impedance and high-impedance readout circuits, respectively. The results show that the sensitivity decrease caused by the gap change with the high-impedance preamplifier is 70%, while the counterpart of the low-impedance preamplifier is 85%. When the gap is 0.1 mm and the width-to-separation ratio varies from 1:1 to 5:1, the sensitivity of the CDT based on the low-impedance preamplifier is increased by 64%, while the counterpart with the high-impedance preamplifier is increased by 22%. Hence, this paper gives the universal guiding rules of preamplification circuit selections for different CDT electrode configurations and application requirements. For a capacitive sensor design with large and unavoidable parasitic capacitance, the low-impedance preamplifier and a CDT with a large electrode width-to-separation ratio match best. For a capacitive sensor design requiring both a large sensitivity and good robustness to out-of-plane interferences, the high-impedance preamplifier and a CDT with a small electrode width-to-separation ratio match best.
变面积电容位移传感器（CDT）由于其高精度和大动态范围而广泛应用于高精度位移测量。前置放大器电路用于将电容变化信号转换为电压，这需要低噪声，对于高灵敏度的变面积 CDT 非常重要。目前的 CDT 前置放大器主要分为低阻抗前置放大器和高阻抗前置放大器；然而，它们的特性和应用范围尚未得到系统比较。本文建立了低阻抗和高阻抗前置放大器的综合模型。然后，设计了具有不同电极间距和间隙的三电极配置，分别用低阻抗和高阻抗读出电路进行位移变化实验。结果表明，高阻抗前置放大器由于间隙变化引起的灵敏度下降为 70%，而低阻抗前置放大器的对应值为 85%。当间隙为 0.1mm 且宽径比从 1:1 变化到 5:1 时，基于低阻抗前置放大器的 CDT 的灵敏度提高了 64%，而高阻抗前置放大器的对应值提高了 22%。因此，本文给出了针对不同 CDT 电极配置和应用要求的前置放大电路选择的通用指导原则。对于具有大且不可避免寄生电容的电容传感器设计，低阻抗前置放大器和具有大电极宽径比的 CDT 匹配最佳。对于需要大灵敏度和对平面外干扰具有良好鲁棒性的电容传感器设计，高阻抗前置放大器和具有小电极宽径比的 CDT 匹配最佳。
