【作者】 常鹏；

【导师】 张涛；

【作者基本信息】 天津大学 ， 检测技术及其自动化装置， 2007， 硕士

【摘要】 涡街流量计因其介质适应性强,无可动部件,结构简单、使用寿命长等诸多优点,在许多行业得到了广泛的应用。而在低流速下,涡街测量就凸显出了它的不足,涡街信号的信噪比很低,有用信号几乎被噪声淹没。普通的涡街流量计采用模拟信号处理方法,在正常流量范围内,涡街流量信号稳定、测量准确、实时性好;而在小流量下,涡街有用信号微弱、提取困难,导致实际测量下限比较高,量程比小,一般为10:1。鉴于上述模拟涡街流量计具有的优势以及存在的不足,本课题研究并且实现了一台数字涡街流量计。该数字涡街流量计采用了双MSP430单片机的硬件结构,在低流速小流量的情况下,由MSP430F1611单片机实现频谱分析算法来计算涡街信号频率,有效地克服了模拟涡街在小流量下测量精度不高甚至不能测量的问题;在正常流量范围内,由MSP430F149单片机对涡街信号前置放大电路输出的方波进行计频,具有常规模拟涡街在高信噪比的情况下测量准确、实时性好的优点。本文主要是按照涡街流量计基本原理介绍、硬件电路介绍、软件设计介绍以及实验数据分析的顺序进行阐述的,主要包括:1.设计了完整的双MSP430单片机的数字涡街流量计硬件电路以及软件程序。成功地实现了一台双MSP430单片机的数字涡街流量计,可以在不同流量之间切换计算频率的方式,从而准确稳定地输出频率。2.成功地实现了数字涡街流量计的4～20mA电流远传功能。并且在DN50和DN25水流管道上做了大量的实验,证明本数字涡街流量计具有较强的抗干扰能力并且大大降低了下限,扩大了量程比,可达到1:35.3～45.5。将此数字涡街分别在天津大学水流量实验装置的管径为50mm和25mm的管道上做了大量的实验。结果表明本数字涡街流量计具有很低的测量下限,有效地扩大了涡街的量程比,抗干扰能力强,实时性好,具有很高的实用价值。更多还原

【Abstract】 The vortex flowmeter is widely used in different fields due to its flexibility to various media, without mobile parts, simple structure and long life etc. However, it has poor performance when operating at low flow rate where the Signal-to-Noise ratio is very small or even the signal is submerged by the noise. The traditional analog vortex flowmeter has benefits of steady signal, high accuracy and good real time in the regular flow range, while it also has a disadvantage of weak signal difficult to detect at low flow rate, which leads to unsatisfying lower limit and a smaller range ratio of 10:1.Inasmuch as the advantages and the shortage mentioned above of the analog vortex flowmeter, a digital vortex flowmeter has been developed successfully. The digital vortex flowmeter is made up of a couple of MSP430 single chip microconputers. It identifies the vortex signals from noises by the frequency spectrum analyzing algorithm in MSP430F1611 single chip computer at low flow rate where the analog one is not accurate, or even can’t work. Meanwhile it works out by MSP430F149 single chip computer the frequency of the vortex signal that is square waves output from pre-amplifier for the vortex signals in the regular flow range where the Signal-to-Noise ratio isn’t too much small, as the analog one is accurate and real time.This paper expatiates with the sequence of the introduction of the vortex flowmeter theory, designment of the hardware and software and analysis of experiment. The main points include:1. The complete circuit and program has been designed. A digital vortex flowmeter with a couple of MSP430 singlechips has been developed successfully. It can choose different method of frequency counting according to variety of the flow and output pulse signal exactly and steadily.2. The digital vortex flowmeter can also output 4～20 mA current. Lots of experiments have been done at DN25 and DN50 pipelines of the water flow experiment facility. It is proved that the digital vortex flowmeter can reduce the disturbance of noise and lower the limit of measurable flow rate. Furthermore, it widens range ratio to 1:35.3～45.5.Lots of experiments on the digital vortex flowmeter have been carried out at DN25 and DN50 pipelines of the water flow experiment facility of Tianjin University. The result shows that the pulse output model digital vortex flowmeter has a satisfying lower limit of measurable flow rate that increases the range ratio effectively, strong antijamming ability and good real time and thus it is of great practicability.更多还原