基于HART总线的智能涡街流量计的研究与开发

【作者】 喻海清；

【导师】 黎亚龙；

【作者基本信息】 中南大学 ， 控制理论与控制工程， 2002， 硕士

【摘要】 现场总线作为过程自动化、制造自动化等领域现场智能设备之间的互连通信网络，建立了生产过程现场控制设备之间以及与更高控制管理层网络之间的联系。而HART总线技术成功的将数字信号通信迭加到现有的现场控制系统上，对改进智能仪表间的通信提供了无风险的解决方案。因此，基于HART总线技术的智能仪表应用最为广泛。 随着数字信号处理器的发展和广泛应用，其高速及对数据的强处理能力日益为人们所认识，将数字处理器运用于参数的实时检测和分析已成为一种发展趋势，它为进一步提高系统的可靠性，实现更为复杂、精确的控制智能创造了条件。 本论文结合长沙矿山研究院的技改项目，研究开发了一种基于HART总线的智能涡街流量计，采用TI公司的新一代超低功耗的混合型信号处理器(MixedSignal Microcontroller)MSP430f149来对流量产生的涡街频率信号进行处理，利用f149芯片的低功耗特性以及片内丰富的外设模块，用纯硬件的方法解决了HART总线设备的低功耗这一技术难关，完全符合HART通信协议技术规范要求。 传统的涡街流量计由施密特触发器产生与流量成正比的脉冲信号(也就是涡街频率信号)，再通过计数器累计得到流量值；但是触发的门限电压在抑制门限电压以下的干扰的同时也限制了仪表的量程下限。本文中设计的智能涡街流量计采用硬件和软件相结合的方案来扩大仪表量程下限。 由涡街产生的原理可知，涡街信号频率与流速成正比，强度与流速的平方成正比。而同一个信号在不同的时期强度相差悬殊。本论文提出在前置的信号调理电路中加入跨导放大器，通过由数字信号处理器产生的PWM信号反馈调节跨导放大器的偏置电流来实现信号调理，力求在到达MD转换模块时都有大致相同的幅值，以便充分的利用MD的字长并减小量化误差。然后，通过自适应陷波滤波算法实时地跟踪涡街信号频率的变化。自适应陷波滤波算法是一种基于预测误差的自适应递归算法，这种陷波滤波器能抑制一个特定频率的窄带信号(陷波频率也就是涡街信号频率)，并且几乎不受带宽以外频率的影响。从而保证对信号频率的精确估计。 由仿真分析可知智能涡街流量计的抗干扰能力强，不但提高了测量精度，而且扩大量程比，适用于气体、蒸汽和低粘度液体等多种介质，具有较高的性价比。更多还原

【Abstract】 Field bus, make relationships between the process control devices and even the high control management network, as a communication network among intelligent instruments in the field of process control automation, manufacturing automation. As HART field bus proposals a solution superimposing the digital signal at the present field control system without risk, the intelligent instruments based on HART technique are widely used.With the development and appliance of the Digital Signal Processing, its high speed and powerful faculty of processing of data are recognized by people. It is a trend to use Digital Signal Processing for a real-time supervisory control and data analysis. The Digital Signal Processing has unexampled predominance in improving reliability, and realizing more complex and more exact control.The intelligent Vortex Flowmeter based on HART field bus, which is introduced in the paper measures the Vortex frequency made from flow signal, combining with the project of ChangSha mining research institute.The intelligent Vortex Flowmeter makes use of powerful processor faculty and abundant module of the newly Ultralow-power consumption Mixed Signal Microcontroller(MSP430fl49) in accord with the technological criterion of HART communication protocol, solving the most difficult technological problem only with device in hardware.The traditional Vortex Flowmeter counts the pulse signals produced by Schmitt trigger that is proportional to Vortex frequency, but the door Voltage that can give rise to trigger not only restrains the noise but also limits the low limitation of the Flowmeter. The intelligent Vortex Flowmeter introduced in this paper expands the low limitation through hardware combining with software.It is proved by the theory of Vortex signal that Vortex frequency is proportional to liquid speed and the amplitude of signal is proportional to the square of liquid speed. The signal amplitude is quite different in the different period.The project of the Vortex Flowmeter adds Transconductance amplifier in the input circuit,and adjusts Transconductance amplifier’s amplifier coefficients realizing the automatic gain control function through PWM signal with feedback.hi addition, the software method traces the frequency of Vortex signal through the adaptive notch filter algorithm, the character of the adaptive notch filter algorithm can be described as below: it is of recursive prediction error(RPE)form and uses a special constrained model(etc. constrained poles and zeros) of infinite impulse response(IIR) with anumber of parameters; The convergent filter is characterized by highly narrow bandwidth and uniform notches of desired shape ;The filter has a transfer function that is 1 almost everywhere but at the site of notch frequency.Through emulation it has a good character of anti-intrusion, and it not only improves the precision but also expends the limitation of Flowmeter. It is applicable to gas,vapor and liquid and it has more performance than cost.更多还原