基于子波变换的单支重构法在涡街流量传感器中的应用

基于子波变换消噪原理,结合涡街流量传感器的实际应用,提出了一种适用于涡街流量传感器频率计数的子波滤波方案,同时给出了滤波级数的选取方法.基于涡街流量传感器工作原理,这种改进的重构计数能够达到计量要求.通过对实测信号的分析,证实了方法的有效性.     

涡街流量传感器应用问题的探讨

本文详尽地分析了涡街流量传感器应用中存在的问题、造成问题的原因,并介绍了涡街流量传感器原理及结构。     

标准涡街流量传感器组合比较法气体流量装置的研究和探讨

本文介绍了用标准涡街流量传感器组合比较法的流量标准装置、检测原理和数据处理方法，解决了大口径气体流量仪表的标定问题。     

涡街流量计在高压风计量中的应用

本文阐述了涡街流量计的工作原理及特点,介绍了利用KTLUD涡街流量传感器和KTZX-2型智能流量积算仪对高压风进行计量的测量系统构成,并结合使用经验就安装和运行过程中的注意事项提出了合理的建议。     

涡街流量计的二次仪表设计

涡街流量计通常由流量传感器(又称一次仪表)和流量显示(又称二次仪表)两大部分组成,本文介绍了一个流量计的设计思路,给出了硬件组成和软件框图.     

两线制低功耗流量显示仪设计

叙述了基于PIC单片机的两线制低功耗流量显示仪的设计方法。给出了利用涡街等流量传感器输出的脉冲频率信号进行计数和利用温度、压力信号进行补偿的流量测量原理。介绍了两线制、低功耗流量显示仪设计和实现过程中的一些关键技术问题。     

差压式涡街质量流量计取压位置的研究

在涡街流量计中，流体通过涡街发生体后会产生压力损失及由旋涡引起的压力波动，根据这一特点，本文提出利用差压检测技术，通过单路差压传感器同时感受由涡街发生体引起的流体双重变化特性，测量流体质量流量的新方法。本文重点对差压检测取压位置进行研究，利用空气和水两种流体介质进行了一系列实验，得到不同取压位置的差压信号与流量关系，确定了能正确测量质量流量的差压取压位置。结果表明，该测量方法结构简单，是测量质量流量的有效方法。     

涡街流量传感器压力损失系数的试验研究与计算

在天津大学电气与自动化工程学院流量实验室的气体流量试验装置上,通过改变管道内气体的压力,对涡街流量传感器的压力损失系数进行试验研究。对大量试验数据进行处理后发现,涡街流量传感器的压力损失系数会随着管道内气体压力的变化而有所变化。当管道内气体压力在0.1～1.1 Mpa的范围内变化时,压力损失系数会随着气体压力的增大而减小,变化幅度最大达到了7%。对压力损失系数随气体压力变化的规律进行分析,并给出压力损失系数随管道内气体压力变化的计算公式。     

涡街流量传感器频率信号的扩频

大口径涡街传感器频率范围很小,单位频率的对应流量很大,配套仪表显示流量的波动大,限制了大口径涡街传感器应用.在此给出了具体的扩频方法来改善此问题.     

插入式涡街流量传感器在水处理系统中的应用

本文介绍LCGB—21插入式涡街流量传感器的基本原理及在水处理系统中的实际应用，并通过实际操作总结出一些工程应用中的维修经验，适用于工程实际。     

Note: anti-strong-disturbance signal processing method of vortex flowmeter with two sensors

Some digital signal processing methods have been used to deal with the output signal of vortex flowmeter for extracting the flow rate frequency from the noisy output of vortex flow rate sensor and achieving the measurement of small flow rate. In applications, however, the power of noise is larger than that of flow rate sometimes. These strong disturbances are caused by pipe vibration mostly. Under this condition the previous digital signal processing methods will be unavailable. Therefore, an anti-strong-disturbance solution is studied for the vortex flowmeter with two sensors in this Note. In this solution, two piezoelectric sensors are installed in the vortex probe. One is called the flow rate sensor for measuring both the flow rate and vibration noise, and the other is called the vibration sensor for detecting the vibration noise and sensing the flow rate signal weakly at the same time. An anti-strong-disturbance signal processing method combining the frequency-domain substation algorithm with the frequency-variance calculation algorithm is proposed to identify the flow rate frequency. When the peak number of amplitude spectrum of the flow rate sensor is different from that of the vibration sensor, the frequency-domain subtraction algorithm will be adopted; when the peak number of amplitude spectrum of the flow rate sensor is the same as that of the vibration sensor, the frequency-variance calculation algorithm will be employed. The whole algorithm is implemented in real time by an ultralow power micro control unit (MCU) to meet requirements of process instrumentation. The experimental results show that this method can obtain the flow rate frequency correctly even if the power of the pipe vibration noise is larger than that of the vortex flow rate signal.     

Mass flowmeter detecting fluctuations in lift generated by vortex shedding

Indirect measurement of mass flow rate has been widely used, combining volumetric flowmeters with the temperature and/or pressure compensation of fluid density. However, this approach has disadvantages, such as a complicated compensating algorithm, and is only applicable to ideal gases, except for highly pressurized and other gases. A flowmeter for direct measurement of mass flow is more suitable for overcoming the disadvantages of indirect measurement. The authors propose one approach to direct measurement using a vortex flowmeter. That is, Karman vortices are generated by a vortex shedder, and fluctuations in the lift and their frequency are detected by stress sensors built into the vortex shedder. The amount of lift is divided by the frequency to yield signals proportional to the mass flow rate. The proposed approach to sensing features simplicity both in principle and in sensor construction. Satisfactory results are obtained from applying this approach to water, air and other gases.     

Performance evaluation of piezoelectric and differential pressure sensor for vortex flowmeters

Piezoelectric and transient differential pressure sensors are two among the most widely employed sensors for vortex flowmeter application. The present study evaluates the performance of these two techniques under fully developed and disturbed flow conditions. Firstly, the location of the transient differential pressure sensor is optimized to obtain high amplitude signals and good linearity in Strouhal number. Empirical mode decomposition method in combination with autocorrelation decay is successfully employed at high Reynolds numbers to identify the vortex shedding frequency in presence of hydrodynamic noise. The performance of the differential pressure sensor deteriorates significantly under disturbed flow conditions at low Reynolds number due to the presence of low frequency components. This deterioration in the signal quality limits the lower operating range of the flowmeter with differential pressure sensor. The output signals of the piezoelectric sensor and differential pressure sensor under no flow condition are compared to obtain the background noise due to piping vibrations and electrical interferences. These results will help a designer to suggest robust signal processing algorithms for vortex frequency detection.     

Computationally lean algorithm of novel optimal FIR adaptive filter for vortex signal extraction

In a vortex flowmeter vortices are generated by a bluff body, inserted in the path of flow, which has a piezoelectric sensor embedded in it. This piezosensor develops a signal having a fundamental frequency that is proportional to flow. The flow measurement relies completely on extraction of true vortex signal and estimation of the correct frequency. A novel adaptive FIR filter has been designed and implemented using low power computational resource (8.25 mW), which gives better results than an existing contemporary system when tested on an industrial flow rig. Further more a comparative study of autocorrelation, EMD Scales filter and proposed algorithm is carried on the good and bad vortex signals. From this comparative study it is seen that proposed algorithm is effective for bad vortex signals and low flowrates where vortex signals are weak.     

A study of mass flow rate measurement based on the vortex shedding principle

Mass flow rate measurement is very important in the majority of industry processes because the mass of fluid is not affected by ambient temperature and pressure as the volume will be. Conventional mass flow rate is normally derived from the volumetric flow rate multiplied by fluid density. The density can be obtained by a densitometer or calculated according to the temperature and pressure measured by a thermometer and pressure gauge respectively. However the measurement accuracy is not always satisfactory. Flowmeters directly measuring mass flow rate have been studied and developed recently, such as Coriolis and thermal flowmeters. Unfortunately they still have some limits in practical applications. A new method in which mass flow rate can be directly measured based on the vortex shedding principle is presented in this paper. As a vortex flowmeter, von Kàrmàn vortex shedding is generated by a bluff body (vortex shedder), leading to a pressure drop and pressure fluctuation. A single differential pressure sensor is employed to detect the pressure difference between upstream and downstream sides of the vortex shedder. Both vortex shedding frequency and pressure drop are contained from the output signal of the differential pressure sensor, so that the mass flow rate can be obtained from the pressure signal. Numerical simulation has been done to analyze the characteristics of the fluid field and design the measurement device. The Computational Fluid Dynamics (CFD) codes Fluent were used in the numerical simulation. Experiments were carried out with water and gas, and the results show that this method is feasible and effective to measure the mass flow rate. This method has also robustness to disturbances such as pipe vibration and fluid turbulence.     

Vortex flowmeter with enhanced accuracy and reliability by means of sensor fusion and self-validation

Due to the complementary qualities of the principles of vortex frequency estimation and vortex time of flight estimation they are ideally suited for an effective sensor fusion within flow measurement. A flow meter which combines the results of the two individual systems in an intelligent manner was built and beside theoretical considerations the performance of the fused system is demonstrated by a variety of measurements. In comparison with conventional vortex meters which only use the vortex frequency to estimate the flow rate, the measuring range can be extended by a factor of 8–10 and the accuracy of the system as well as the robustness to disturbances like a second fluid phase or depositions on the bluff body are strongly increased.     

涡街流量计数字信号处理方法

涡街流量计是最近发展起来的一种新型流量计，其传感器输出信号的频率与流体的流速成正比，经过计算可以测量积流量。由于管道的机械振动和流场的不稳定等因素，使得传感器输出信号中含有各种噪声，本文归纳了几种通过数字信号处理测量频率的方法，其中小波变换方法具有较好的应用前景。     

涡流管制冷分析

对涡流管制冷本质并进行相关的试验研究,进行理论分析,以及对四流道喷嘴涡流管的速度和温度分布进行数值模拟,结果表明:涡流管内实际流场由轴向,径向和漩涡运动组成,其流动形态在轴向上为阿基米德螺线,在横截面上为强制涡—自由涡的模型;管内流体能量的分离主要发生在涡流室区域附近,且气体从喷嘴出来后有少量直接进入冷端孔与冷气流混合,从而影响涡流管制冷效率。     

Analysis of signals from vortex flowmeters

The vortex flowmeter is used to measure the flow of fluids especially where the requirements include wide rangeability and the use of flowmeters with no moving part. It is common knowledge that process conditions affect the operation of a vortex flowmeter, and a customary approach is to introduce flow conditioners so that the measurement output from a vortex flowmeter conforms to specified standards. Some recent studies have shown how to apply signal analysis to the signal from vortex flowmeters to enhance performance, but the signal which has been typically analysed is the pulse train. In this paper,we advocate a new approach which involves detailed analysis of the unconditioned signal from the sensor prior to conventional signal conditioning. The results obtained from this approach open opportunities for the development of alternative signal conditioners and transmitters which not only enhance the quality of the measurement output from a vortex flowmeter but also make it possible to use the flowmeter for monitoring the condition of the plant.