低温漂高精度柔性电容传感器阵列检测电路

A detection circuit for flexible capacitor sensor array with low-temperature drift and high accuracy

为了抑制温度和屏蔽电缆的寄生电容对柔性电容传感器检测精度的影响,设计了一种低温漂高精度柔性电容传感器检测电路.基于电容对交流信号的容抗与容值的关系,采用运算放大式的C/V转换电路将待测电容传感单元的容值转换为交流信号的幅值,再通过精密整流电路将其转换为直流电压输出;针对传感器应用环境温度变化较大的情况,采用具有自动增益控制的文氏电桥振荡电路产生正弦交流信号,选用具有零温度系数点的结型场效应管作为可变电阻,极大地减小温度变化对输出幅值的影响;采用双层屏蔽的方式与C/V转换电路搭配,极大地抑制屏蔽电缆引入的寄生电容以及电容传感阵列中其他传感单元对待测传感单元的影响.实验表明,测量5~50 pF电容时,测量值与采用LCR测试仪测得的准确值的最大相对误差为1.70%;温度从-40℃变化到100℃,输出正弦信号的幅值只变化了0.88%;1 m长的RG316同轴屏蔽电缆的寄生电容(93 pF)只使检测结果漂移了0.16 pF.

In order to suppress the influence of temperature and parasitic capacitance of shield cable on the detection accuracy of flexible capacitive sensor,a low-temperature drift high-precision flexible capacitive sensor detection circuit is designed.Based on the relationship between capacitive reactance and capacitance value on the AC signal,the latter of the sensor unit under tests is converted into the amplitude of AC signal by C/V conversion circuit of operational amplification,and then converted into DC voltage output by precision rectifier circuit.In view of the large temperature variation of the sensor application environment,the Wien bridge oscillator circuit with automatic gain control is used to generate sinusoidal AC signal,and the junction field effect tube with zero temperature coefficient point is selected as the variable resistor to greatly reduce the influence of temperature change on the output amplitude.The double layer shield is used to match the C/V conversion circuit to greatly inhibit the influence of the parasitic capacitance introduced by the shield cable and other sensor units in the capacitor sensor array on the measured sensor unit.Experiment results show that the maximum relative error between the measured value and the accurate value measured by LCR tester reaches 1.70%within the capacitance range of 5-50 pF.When the temperature varies from-40℃to 100℃,the amplitude of the output sinusoidal signal changes by merely 0.88%.The parasitic capacitance of 1 m-long RG316 coaxial shielded cable equals 93 pF,resulting in the detection result drift of 0.16 pF only.