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Development status of several flow meters
2011-5-19 10:51:31

   流量计 Time-of-flight ultrasonic flowmeter

5% 变到 8% ,即反映面平均流速的流量比体平均流速的流量偏大 5%~8% The current time-of-flight ultrasonic flowmeter is actually a radial flowmeter type plug-in flowmeter (except for the external clamp type), which determines the average surface velocity, and the flow rate should be reflected by the volume average velocity. If the velocity distribution is axisymmetric, And in order to fully develop the tube flow, there is a certain proportional relationship between the average surface velocity and the body average velocity. When the flow rate changes (that is, the Reynolds number), the difference between the two average velocity can be changed from 5% to 8% , which reflects the surface average. The flow rate of the flow rate is 5% ~ 8% larger than the volume flow rate . The problem is that there is no simple relationship between the two average flow speeds due to the distortion of the speed distribution and the swirling flow in the field application. GERG 2004 年对目前世界上最著名的几家气体超声流量计生产厂产品进行不良安装条件下测试,证明多声道气体超声流量计对阻流件干扰仍然敏感,甚至达到 1.2% 的测量偏差。 The multi-channel type is developed by the time difference ultrasonic flowmeter to suppress the interference of choke pieces. People hope to use multi-channels to form a channel network. A computer can analyze the distribution distortion and rotational flow of the entire pipe cross-section, and formulate instrument signal processing. The scheme obtained high measurement accuracy. In 2004 , the European Gas Testing Alliance ( GERG ) tested the products of several of the world's most famous gas ultrasonic flowmeter manufacturers under poor installation conditions, proving that the multichannel gas ultrasonic flowmeter has resistance to resistance. Flow piece interference is still sensitive, even reaching a measurement deviation of 1.2% . In addition, due to the variety of ultrasonic flowmeter sensor structure types, field test data of a manufacturer's products may not be available for borrowing from other manufacturers. The international standard for gas ultrasonic flowmeters is in the process of being drafted. The draft standard specifically proposes to formulate the characteristics of the instruments calibrated in the laboratory to the characteristics of field instruments. How to maintain the characteristics conversion is an important content. It is the first of all current international standards. When this requirement is raised, it also reflects from the side that this problem is a core issue for this type of flowmeter . —— 噪声影响必须予以关注。 Another tricky issue is reflected in the draft standard noise effects must be addressed . The noise sources in the process pipelines are pipe fittings and valves. The situation is random and complex. How to overcome these factors has been proposed. However, a large number of tests and certifications are required to be included in the standard. 21 世纪流量计是有一定根据的,它具有一系列特点为其它类型流量计所不及,但是从上述介绍可见,要达到期待的优良特性及实际应用尚有一段相当艰巨的路程,应该相信,困难是可以克服的,只要投入足够的研发力度,实现的日子就会到来。 It should be pointed out that in recent years, the internationally respected ultrasonic flowmeter for the 21st century flowmeter has a certain basis. It has a series of characteristics that are incomparable to other types of flowmeters . However, it can be seen from the above introduction that it is necessary to achieve the expected excellent characteristics and practical application. There is a rather arduous journey. It should be believed that difficulties can be overcome. As long as sufficient research and development efforts are invested, the day of realization will come.

EMF Electromagnetic flowmeter (hereinafter referred to as EMF )

EMF 遵循的工作原理法拉第电磁感应定律,仪表的流量(流速)仅与流体流速有关,不受流体的密度、黏度、温度、压力以及一定范围内的电导率变化的影响,但是实际上由于仪表的结构型式、安装条件及使用现场条件的差别,实践证明,这些影响量对流量计的测量准确度是有一定影响的,特别是高准确度级别时这些影响已不容忽视。 According to the working principle of EMF , Faraday's law of electromagnetic induction, the flow rate (flow rate) of the meter is only related to the flow rate of the fluid. It is not affected by the density, viscosity, temperature, pressure of the fluid, and the change in conductivity within a certain range. The differences in the structure type, installation conditions, and field conditions of practice have proven that these influences have a certain impact on the measurement accuracy of the flowmeter , especially at high accuracy levels. These effects cannot be ignored. 年国际仪表用户协会( WIB )委托荷兰 TNO (荷兰应用科学研究组织)和荷兰 DSM 研究所对 8 家电磁流量计制造厂提供的 20 台准确度优于 1% 流量计进行影响量的研究试验,试验历时 2.5 年,影响量有流体电导率、黏度、流体温度、环境温度、管道尺寸,衬里材料等。 In 1990 , the International Instrument User Association ( WIB ) commissioned the Netherlands TNO (Netherlands Applied Scientific Research Organization) and the Netherlands DSM Institute to conduct research on the influence of 20 flow meters provided by 8 electromagnetic flow meter manufacturers with an accuracy better than 1% . The test lasted 2.5 years. The influences include fluid conductivity, viscosity, fluid temperature, ambient temperature, pipe size, lining material, etc.

General instrument factory product instruction manuals indicate the value of the conductivity threshold (lower limit) for a certain type of electromagnetic flowmeter , indicating that it cannot be lower than the threshold. If it is lower than the threshold, it will increase the indication error until it cannot be applied. 试验证明流量计在阈值附近示值误差甚至有 1%~6% 的变化,仪表生产厂提供的阈值数值是在实验室理想工作条件下得到的,而使用现场受流体电导率均匀性、连接信号线、外界噪声等的影响,需要提高阈值。 The WIB test proves that the error of the displayed value of the flowmeter near the threshold value even changes from 1% to 6% . The threshold value provided by the instrument manufacturer is obtained under the ideal working conditions of the laboratory. The influence of signal lines and external noise needs to increase the threshold. For example, an order of magnitude can be measured correctly. The flow rate of a low flow rate has a greater impact than the flow rate of a high flow rate. The effect of a small-caliber instrument is greater than that of a large-caliber instrument. 5 15 75 200mm2/s cst )中试验,证明示值误差变化在 0.7%~1.6% ,变化最大的一台仪表近 4% The effect of liquid viscosity is tested in some media: viscosity of sugar, water solution, and glycerin solution are 5 , 15 , 75, and 200mm2 / s ( cst ), which proves that the error of the displayed value varies from 0.7% to 1.6% , and the instrument with the largest change Nearly 4% . The characteristic curve (with Reynolds number) of the medium whose viscosity is different from that of water cannot be represented by the characteristic curve of water calibration. The influence of liquid temperature and ambient temperature on other parameters (such as conductivity, viscosity, etc.) affects the accuracy of flowmeter measurement, and is more sensitive to small-caliber and low-flow instruments.

20 ~45 内试验,对 DN10~DN40 示值偏移达 0.2%~0.3% The test of WIB in 20 ~ 45 , the deviation of the indication value of DN10 ~ DN40 reaches 0.2% ~ 0.3% . The adhesion and precipitation of fluid impurities in the pipeline will significantly affect the characteristics of the instrument, and the error of the displayed value cannot be ignored. If the conductivity of the attachment is greater than the conductivity of the liquid, the measured flow value is low. If the conductivity is low, the measured value is high. The liquid contains air bubbles, which vary depending on the flow pattern of the air bubbles. If the electrode is covered, the signal is output. It shakes and doesn't even work properly. 10D 已可抗严重干扰,如空间双弯头,各种阀开度。 Among several commonly used flowmeters , electromagnetic flowmeters have strong resistance to interference from under-developed pipe flow. Generally, the length of the front straight pipe section 10D can resist severe interference, such as space double elbows and various valve openings. GB/T18660 GB/T18659 JISB7554 ZBN12007 等)中有一些表列数据,但与 ISO5167 比较,无论明细方面及成熟程度差距较大。 There are some tabulated data in the standards ( GB / T18660 , GB / T18659 , JISB7554 , ZBN12007, etc.), but compared with ISO5167 , there is a large gap in terms of details and maturity.

TUF Turbine flow meter (hereinafter referred to as TUF )

是受流体条件影响严重的流量计 ,在物性方面:液体 TUF 受黏度影响较大,气体 TUF 较小;受密度影响,则气体 TUF 较大,液体 TUF 较小;在流体流动特性方面: TUF 应有足够长的直管段长度或安装流动调整器,在流体性状方面,腐蚀磨蚀、结垢、脏污、堵塞会严重影响流量计特性直至不能正常工作。 TUF is a flowmeter that is seriously affected by fluid conditions. In terms of physical properties: liquid TUF is more affected by viscosity and gas TUF is smaller; affected by density, gas TUF is larger and liquid TUF is smaller; in terms of fluid flow characteristics: TUF There should be a long enough straight pipe length or a flow regulator. In terms of fluid properties, corrosion and abrasion, scaling, dirt, and blockage will seriously affect the characteristics of the flowmeter until it can not work normally. TUF 是发展较早的一类流量计,它已颁布相当完备的标准规范文件,如 ISO2715 ISO9951 OIMLR6 R32 AGAN07 PrEN12261 JISZ8765 JISB7501 等。 In the new type of flowmeter , TUF is an earlier type of flowmeter. It has issued quite complete standard specifications, such as ISO2715 , ISO9951 , OIMLR6 , R32 , AGAN07 , PrEN12261 , JISZ8765 , JISB7501 and so on. ISO5167 有显著的差别,它缺少 ISO5167 的三个特点,因此我们难以藉助标准文件对仪表现场准确度的影响量进行修正。 However, these standard files are significantly different from ISO5167 . It lacks the three characteristics of ISO5167 . Therefore, it is difficult for us to use the standard files to correct the influence of the accuracy of the instrument site. 的检测件无法提出统一的结构形状和技术要求,因此统一的流出系数(或仪表系数)是不存在的,当然现场影响量对不同的结构形状是会产生不同的影响的。 TUF 's test pieces cannot propose a uniform structure shape and technical requirements, so a uniform outflow coefficient (or meter coefficient) does not exist. Of course, the amount of field influence will have different effects on different structure shapes. TUF 特性更上一层楼,因此统一结构形状不是此类流量计的选择。 Structural shape innovations will take TUF characteristics to the next level, so a uniform structural shape is not an option for this type of flowmeter . TUF 为保持高准确度在现场配备在线校验系统,如天然气输配气站,但是在城市企业或公用事业的应用就难以实行这种措施,如何确定现场准确度仍然是值得探讨的课题。 At present, TUF is equipped with an online calibration system at the site to maintain high accuracy, such as natural gas transmission and distribution stations, but it is difficult to implement such measures in the application of urban enterprises or utilities. How to determine the site accuracy is still a topic worth exploring .