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Applications of Weak Capacitance/Conductance Measurement Techniques in Process Industry

Author: ZhuJianPing
Tutor: HuangZhiYao；WangBaoLiang
School: Zhejiang University
Course: Detection Technology and Automation
Keywords: Weak Signal Detection Capacitance Conductance Charge - transfer method Bipolar pulse current
CLC: TM934
Type: Master's thesis
Year: 2006
Downloads: 290
Quote: 9
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Abstract

Process industry, there are a large number of parameters need to be measured, but often signal is relatively weak, it is difficult to use traditional measurement methods directly, which requires the study of weak signal detection technology. Because many parameters were measured by detecting the capacitance or conductance indirectly to achieve, so important to the application of weak capacitance / conductance detection technology in the process industry. Weak signal detection technology, and try the weak capacitance / conductance detection technology used in the process industry. The main work is as follows: 1. Developed based on the measurement principle of the charge transfer method, a weak capacitance measurement system. The system can effectively suppress stray capacitance on the measurement results, and the circuit is simple. The switch control signal generated by a dedicated circuit; timing control is completely implemented by a hardware circuit, do not need to go back to the software; direct output of the measuring circuit and the capacitance value corresponding to the voltage value; frequency selection can be achieved through the jumper, in order to meet different applications For measuring the frequency of the request. Capacitance measurement technology is applied to the the TWP column chromatography section, the relationship between the capacitance value of the solution and Wilforlide alcohol and Wilforlide diol content analysis, using the results of capacitance measurements to indicate the solution Thunder content of of rattan the lactone alcohol and Wilforlide glycol, TWP column chromatography section line monitoring. Design capacitive line detection system able to accurately guide the end of the preceding paragraph, to effectively control the effects of triptolide in Polyglycoside content, and makes the middle of 4-6 hours in advance to start, which TWP yield from the original of 27.5 ‰ increased to approximately 28.5%. 2 Research the weak conductance measurement technology based on bipolar pulse current excitation principle. This method is equal to the excitation source level amplitude of the positive and negative cycles, the opposite polarity to avoid the DC excitation is easy to produce the electrode polarization. And motivate any half cycle, the electrode can be seen as incentives by the DC signal detection electrodes directly on the DC output signal, eliminating the need for the traditional AC incentives complex and time-consuming signal processing chain, to meet some real-time high requirement applications. The four-electrode measurement, the measurement technique can measure a single point of the conductivity of the solution, but also by improving the sensor to achieve the solution of multi-point conductivity measurement. The measurement technology applied to a 16 electrode resistance tomography system, bipolar pulse current is applied sequentially in a different pair of electrodes, and then measure the voltage signal on the other pair of electrodes using a suitable image reconstruction algorithm to obtain a measured reflected the cross-sectional image of the distribution media. The experiments show that, based on the principle of ERT technology is feasible and effective. 115.2Kbps baud rate, real-time imaging system speed is about 20 per second; Without real-time imaging, data acquisition rate of about 80 per second. At the same time the introduction of the charge releasing circuit to improve the stability and resolution of the system.

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