Matko Vojko
Faculty of Electrical Engineering and Computer Science, University of Maribor, Koroška c. 46, 2000 Maribor, Slovenia.
Sensors (Basel). 2022 Jul 3;22(13):5030. doi: 10.3390/s22135030.
We present a new highly sensitive, low-value capacitance sensor method that uses multiple quartz crystals connected in parallel inside the oscillator. In the experimental setup, the measured (sensible) reactance (capacitance) is connected in parallel to the total shunt capacitance of the quartz crystals, oscillating in the oscillator. Because AT-cut crystals have a certain nonlinear frequency−temperature dependence, we use the switching mode method, by which we achieve a temperature compensation of the AT-cut crystals’ frequency−temperature characteristics in the temperature range between 0−50 °C. The oscillator switching method also compensates for any other influences on the frequency of the oscillator, such as ageing of the crystals and oscillator elements, supply voltage fluctuations, and other parasitic impedances in the oscillating circuit. Subsequently using two 50-ms-delayed switches between the measuring and reference capacitors, the experimental error in measuring the capacitance is lowered for measurements under a dynamic temperature variation in the range of 0−50 °C. The experimental results show that the switching method, which includes a multiple quartz connection and high-temperature compensation improvement of the quartz crystals’ characteristics, enables a sub-aF resolution. It converts capacitance changes in the range 10 zF−200 fF to frequencies in the range 4 kHz−100 kHz.
我们提出了一种新型的高灵敏度、低阻值电容传感器方法，该方法在振荡器内部使用多个并联的石英晶体。在实验装置中，被测（敏感）电抗（电容）与石英晶体的总并联电容并联，在振荡器中振荡。由于AT切型晶体具有一定的非线性频率-温度依赖性，我们采用开关模式方法，通过该方法在0-50°C的温度范围内实现对AT切型晶体频率-温度特性的温度补偿。振荡器开关方法还补偿了对振荡器频率的任何其他影响，如晶体和振荡器元件的老化、电源电压波动以及振荡电路中的其他寄生阻抗。随后，在测量电容和参考电容之间使用两个延迟50毫秒的开关，在0-50°C的动态温度变化范围内进行测量时，测量电容的实验误差得以降低。实验结果表明，包括多个石英连接和石英晶体特性高温补偿改进的开关方法能够实现亚飞法分辨率。它将10 zF-200 fF范围内的电容变化转换为4 kHz-100 kHz范围内的频率。
