Study On Engineering Electrical Conductivity Measurement Technology And Its Applications

The electrical conductivity is one of the basic characteristics of liquid included multi-phase system. As the conductivity value is commonly related to the internal property of the research object, the concerned measurement technique have long been used to study the internal property of liquid included multi-phase system. Although the electrical conductivity measurement technology has been studied extensively, the variety and complexity of the measurement objects in laboratory research and industrial field demand the development of measurement method relevant to the object so as to enhance the accuracy of the measurement of electrical conductivity and its distribution.When single value conductivity is measured, the measured value is usually related to the frequency of the signal exciting the sensor. But in commonly used conductivity instruments, the sensors are excited with signals of fixed frequency, this can make the correct conductivity measurement of some objects impossible. A frequency-variable conductivity measurement method was proposed and a conductivity measurement instrument was developed which incorporated a frequency-programmable signal source. The instrument was designed in a lock-in amplifier structure, with the advantages of compact structure and good stability. It can measure the conductivity of multi-phase flow correctly in the frequency range of 0-1.25MHz.Concerning the study of electrical conductivity distribution measurement technology, the work was focused on the performance improvement of electrical resistance tomography (ERT) system. Based on bi-directional pulse technique, a high speed ERT data acquisition system was developed. Ideas were borrowed from the researches in electrical capacitance tomography (ECT) system; a new ERT image reconstruction algorithm was designed.The main work and contributions are as follows:(1) As the conductivity measurement result is related to the frequency of the signal exciting the sensor , a frequency-variable conductivity measurement method was firstly proposed and a conductivity measurement instrument was developed which incorporates a frequency-programmable signal source. The instrument was designed in a lock-in amplifier structure, with the advantages of compact structure and good stability. The direct digital synthesis (DDS) ICs were used to produce signals of programmable frequency and phase, wide band low pass filters and programmable amplifiers were elaborately designed to guarantee the good performance of the instrument. The instrument can measure the conductivity of multi-phase objects correctly in the frequency range of 0-1.25MHz.(2) The conductivity and the concentration of triperygium wilfordii of the extract of a countercurrent leaching process were determined and the correlation between the solution conductivity and triperygium wilfordii concentration was described with a mathematical model. Based on the proposed model, the concentration of triperygium wilfordii of the extract was estimated from the conductivity measurement result, the monitor of the countercurrent leaching process of triperygium wilfordii was realized.(3) A high speed data acquisition system of ERT was developed based on bi-directional pulse current technique. The electrodes of the ERT were excited by a bi-directional current, during whose each half cycle the current flowing through the driving electrode pair was kept constant, the influence of electrode polarization was reduced. The bottlenecks which limit the data acquisition speed in AC excited ERT system were partly eliminated. During the measurement period, the sensors could be taken as excited by a quasi-DC current, the time-consuming filters necessary for the traditional AC-excited ERT system were simplified without influence to the accuracy of the data acquisition result. Compared with the traditional ERT data acquisition systems, the data acquisition speed was increased from 50 frames/second to 110 frames/second (104 samplings /frame).(4) Based on ideas borrowed from the research result in ECT, a modified linear back projection(LBP) algorithm for ERT was developed. In stead of the sensitivity map,a coefficient matrix derived through an off-line optimization process was used in the linear back projection (LBP) algorithm for online ERT image reconstruction. Simulation and experimental results show that the image quality of the new algorithm is much better than the image quality of the LBP, and its image reconstruction speed is the same as that of the LBP. The target of reconstructing good ERT images at high speed was reached...