【作者】 杨富广；

【导师】 石天明；

【作者基本信息】 中国石油大学 ， 控制科学与工程， 2010， 硕士

【摘要】 本文根据电阻层析成像(ERT)技术的相邻测试原理,设计了ERT数据采集系统样机,并对样机进行了测试。它包括以下电路设计:设计了基于直接数字合成(DDS)技术的幅度、频率可以数字控制的激励源,通过增加反馈通道提高了传统双运放电压控制电流源(VCCS)电路的带负载能力。利用复杂可编程逻辑器件(CPLD)设计了相邻测量模式的ERT电极选通逻辑控制器,这种设计可以最小化更改硬件设计而实现其他方式的ERT测量。将滤波器置于前置放大电路的反馈通道中,这样不仅去除了电极信号的直流偏置电压,而且避免了在正向通道中直接采用交流耦合引起的相位误差。还设计了程控放大、开关解调、低通滤波等功能电路实现了对ERT微弱信号的调理。采用高速AD转换器实现了数据采集,采集数据稳定度高,最大误差为3LSB。通过USB2.0接口实现了上位机对数据采集装置的控制。编写了基于Visual Basic 6.0的数据采集软件,实现了对激励源大小和频率、程控放大器初始增益、采样速率等参数的设置。图像重建算法是COM化的线性反投影(LBP)成像算法,而且该COM模块被集成到了数据采集软件中。论文还给出了16电极ERT测试装置的实验结果,测试了不同电导率液体下的信号并确定出圆形塑料棒的位置,并对相应结果做了分析。该数据采集装置样机使用方便,可以为今后的研究工作提供数据支持。更多还原

【Abstract】 In this thesis, a tested prototype of data acquisition of an Electrical Resistance Tomographic (ERT) measurement system is presented, according to the principle of adjacent method. It entails the following circuit designs: A measuring current source is formed by a chip of direct digital synthesis (DDS) technology whose amplitude and frequency is programmable. The loading capacity of a traditional dual-opamp structured voltage controlled current source (VCCS) is enhanced by implementing a feedback channel design. A CPLD circuit based electrode selection controller, using the principle of adjacent measurement method, is designed. Such a design permits the flexible modification of ERT measurement strategy but would minimize the hardware change should such modification is necessary. The preamplifier is implemented in such a way that a special filter is embedded in the feedback channel to remove the offset DC voltage as well as reduce the phase error introduced from the direct AC coupling in the forward channel; Other designs include a programmable gain amplifier, a switch demodulator, and a lowpass filter to condition the weak analog signal; The data acquisition circuit is formed by a high speed AD which is found stable with a maximum error of 3LSBs; The measuring device (slave unit) can be controlled by a host computer through a USB interface; A Visual Basic 6.0 based data acquisition software is designed which is able to set the frequency and amplitude of current source,the initial gain of amplifier, the data acquisition speed etc. The tomographic image reconstruction is performed by a COM module that implements the Linear Back Projection (LBP) algorithm. This COM module is integrated into the data acquisition software. The experimental results obtained from a test section that contains 16 electrodes are also described in the thesis. Measurement of signal response with regarding to liquids of different conductivities and phantom (a circular plastic rod) positions are given and analysis is performed accordingly. The prototype is very easy to use and it can supply ERT measurement data for future research work.更多还原