电磁流量计电场动态平衡过程分析

从电磁流量计电场的基本公式出发，分析了电极截面内电场的建立过程及平衡过程，指出涡电流场在电极截面内分布的动态平衡性。结合相应的边界条件，计算了平衡状态下涡电流场的分布及其对传统电磁流量计及多电极电磁流量计测量值的影响。通过数值计算及定量分析，证明了多电极电磁流量计弦端压差测量方法的有效性。该研究有助于深入分析电磁流量计的工作原理及指导多电极电磁流量计的设计。     

多对电极电磁流量计传感器电极阵列设计

在多对电极电磁流量计系统中，传感器电极阵列的设计影响到整个流量计系统的测量精度。为了得到更高的测量精度，在介绍了多电极电磁流量计基本原理的基础上，用有限差分法求解了电磁流量计的基本方程，并采用弦端压差测量方法研究了不同的电极数目和电极尺寸对平均流速估计的影响，以及这两方面及其他物理条件如管道直径、后继转换电路阻抗匹配在电极阵列优化设计中的相互制约关系。为多电极电磁流量计的电极阵列设计提供了具体而明确的设计准则。     

电磁流量计的正确安装与使用

电磁流量计作为一种成型的速度式流量计,在工业导电性流体流量测量方面广为应用。简述电磁流量计的原理、构成、安装、使用要求,并对常见故障进行分析,说明正确使用电磁流量计的方法。     

电磁流量计衬里和电极对流体噪声影响及工艺处理方法

提高电磁流量计衬里和电极的加工粗糙度水平,从本质上降低流体噪声产生的几率和幅度,从而提高流量计测量的灵敏度和稳定性。本文从传感器衬里和电极粗糙度引起电磁流量计动态零点的流体噪声分类、产生,引导出能够降低流体噪声提高信噪比的重要措施,并介绍电磁流量计传感器制造中一些关键工艺措施。     

科技新成果信息

防爆电磁流量计防爆电磁流量计主要解决防爆场合耐腐蚀性流体介质的流量测量和计量问题,广泛用于化工、化纤、化肥、冶金、矿山等工业领域,具有明显的经济效益和推广价值。该产品设计合理,尤其在电极本安防爆电路、一体型结构、耐腐蚀衬里材料的选择、隔爆型外壳等方面有所创新。作为防爆电磁流量计的自行设计和开发,填补了国内产品的空白。该产品由于具有安装使用方便的特点,因而受到用户的欢迎。     

管道对电磁流量计敏感场影响研究

运用有限元软件ANSYS对电磁流量计中存在非导电物体建立的仿真模型,研究了不同内径管道对电磁流量计敏感场响应特性的影响,为电磁流量计测量两相流时传感器电极尺寸设计提供一定的参考,也为电磁流量计在一定管径下两相流测量的误差分析提供理论依据。     

多相流多电极弦端电压测量

以电磁感应定律为基础,提出采用多对电极来研究多相流电磁流量计感应电压特性方法,建立了电磁流量计的三维模型,获得了横截面上感应电位的分布规律,分析了电极上的感应电位沿流体管道圆周的分布规律、电极两端的弦端电压与电极对坐标位置的关系、电极电压与电极对所处位置弦长的关系和电极电压与弦长的比值和电极对所处位置的关系.证明多电极测量弦端电压可以用于多相流连续相的速度特性测量与分析.     

双激励电磁流量计的研究

在对电磁流量计技术的不断研究中认识到,电磁流量计传感器具有电极与导电流体间的特有关系,可以引入一个电压激励下的新的阻抗分压测量关系,使电磁流量计传感器在磁场与电压两种激励下以交替方式工作,组成两个参数的测量关系,形成一种新型的双激励电磁流量计。     

两种新型电磁流量计及其应用

本文介绍了两种新型流量计——无电极式和双频励磁式电磁流量计的结构原理及其特点和应用领域的扩大,并给出了一些有价值的实验数据。     

包含电极尺寸及位置信息的电磁流量计干标定模型

现有电磁流量计干标定模型中,电极尺寸、位置均被作了理想化处理,即假设电极尺寸无穷小、电极位于测量管段正中间的两个对称点上,两对称点连线与磁场垂直。这类理想化的模型与实际情况差异较大,限制了干标定的精度,并对产品一致性提出了很高的要求。针对这一问题,采用分离变量法建立了包含实际流量计电极尺寸及位置参数的电磁流量计干标定模型,比现有干标定模型更接近于实际流量计,有利于提高干标定精度,降低对产品一致性的要求。通过与现有模型及数值仿真的对比分析,验证了该模型的准确性。     

On the effect of the electrode shape and contraction section on the right-angled electromagnetic flowmeter

Flow measurement is of great importance in many industries, such as the chemical industry, energy and urban drainage. Electromagnetic flowmeter is widely used due to its wide range, high response and suitability for multiphase flow detection. To meet the needs of small-caliber and low-flow applications and wider installation scenarios, this paper proposes a new insertion-type right-angled bent electromagnetic flowmeter. The measurement signal of the electromagnetic flowmeter is closely related to its internal fluid flow state, thus computational fluid dynamics (CFD) method is used to optimize the electrode shape and contraction section shape of the electromagnetic flowmeter. Through comparison experiments of flat electrodes and cone electrodes, a better model is obtained. Furthermore, three new models of the contraction section are proposed: the sharp contraction type, the gradual contraction type, and the Widosinski curve contraction section. The Widosinski curve contraction section is easier to stabilize the flow field inside the flowmeter. The experimental data are in good agreement with the results of the large eddy simulation, and the results show that the measurement performance of the cone electrode is better than that of the flat electrode. When measuring small flow rates, the error of the cone electrode is only 5%, much smaller than the error of the flat electrode. The findings of this study provide a new idea for the development and optimization of the measurement performance of the right-angled electromagnetic flowmeters.     

高压电磁流量计电极结垢的解决方案

当测量介质具有易结垢的特性时,常规的高压型电磁流量计难以满足测量要求。为了解决此行业难题,本文对测量导管结构以及测量电极的形状做改进设计,由此可极大地延长此类工况条件下电磁流量计的无维护使用寿命。     

Problems in the theory and design of electromagnetic flowmeters for dielectric liquids. Part 3a. Modelling of zero drift due to flux linkage between coil and electrode cables

This paper investigates theoretically the magnitudes of zero offsets and zero drifts originating from magnetic flux linkage between the coils of the electromagnet and the loop formed by the electrode cables in an electromagnetic flowmeter for dielectric liquids. The dependence of such zero offsets on liquid properties, frequency of operation, etc. is explained. The paper gives the results of measurements of the effective electrical conductivity and permittivity of dielectric liquids BP180 and Castrol OX-9 (and mixtures of these) in the frequency range 1 Hz–1 kHz. These are used to predict the zero offsets expected in metering these liquids using phase sensitive detection with the flowmeter tube described in Part 1 of the paper. Precautions needed in flowmeter design to minimise instrument zero offsets and zero drifts are explained. The electromagnetic flowmeter theory was developed at Cranfield and the determination of the electrical properties of the dielectric liquids was carried out at QinetiQ.     

Development of an optimised magnetic field source for flowmeter applications

Sensitivity of a magnetic flowmeter relies on many factors like magnetic field strength, gap between electrodes, material properties, magnet temperature etc. For a given measuring conditions, a strong magnetic field source can produce highest sensitivity for the flowmeter. An economic design of magnetic field source would be to produce the strongest magnetic field from a given amount of magnetic material. In this paper, various magnet configurations are analyzed using FEM and the flowmeter sensitivity using such magnet configurations are compared. It is observed that magnets arranged in a Halbach fashion produce the highest sensitivity for the flowmeter using a given amount of magnetic material. The major challenge for the development of such a magnetic field source is its fabrication from its constituent magnets, combatting their huge attractive/repulsive forces (∼2500 N for our case). Therefore, a specific mechanical tool has been designed for assembling the magnetic field source and a robust assembly technique has been devised using numerical computations. The designed magnetic field source produces a peak magnetic field of 0.78 T in the pole cross section of 50 mm × 50 mm.     

Streaming current noise generation in electromagnetic flowmeters measuring conducting fluids

This paper provides a model of streaming current noise generated by the interaction of turbulence with the charge distribution which occurs in the liquid, close to the surface of the insulating liner of an electromagnetic flowmeter, as a consequence of charge species being absorbed by the lining material itself. Such noise is present whether the electromagnetic field of the flowmeter is excited or not. It is shown in this paper that this noise can be detected in potable water at a conductivity of order 5 mS/m, although at such levels it is often masked by the first stage amplifier noise, but that it becomes more significant when measurements are made in de-ionised water where the conductivity may be as low as 5 μS/m. The predicted spectral characteristic of the noise and the dependencies of the noise on the conductivity of the fluid, the pipe size and flow velocity provided by the model are all shown to be in good agreement with experimental data. The model is valid for clean aqueous fluids, where there is no noise generated by particle impact or significant electrochemical reaction between the fluid and the sensing electrodes. It can be used to predict the signal to noise ratios in electromagnetic flowmeters using different excitation waveforms and frequencies or different electrode structures.     

A technique for low cost calibration of large electromagnetic flowmeters

The need for calibration of electromagnetic flowmeters adds considerably to the cost of these instruments especially in the larger sizes. This paper discusses a proposed technique for calibration of large electromagnetic flowmeters which avoids the need for a calibration flow rig. The technique consists essentially of filling the flowmeter tube with water, operating the electromagnet as it would be operated in normal flowmeter operation and measuring the axial component of the eddy current electric field in the water over each electrode. This allows the calibration factor for a flat velocity profile to be determined.     

Flow measurement with an electromagnetic flowmeter in two-phase bubbly and slug flow regimes

In order to investigate the characteristics of an electromagnetic flowmeter in two-phase flow, an alternating-current electromagnetic flowmeter was designed and manufactured. The signals and noise from the flowmeter under various flow conditions were obtained, and analyzed in comparison with the flow patterns observed with a high-speed charge-coupled device camera.

An experiment with void simulators, in which a rod-shaped non-conducting material was used, was carried out to investigate the effect of bubble position and void fraction on the flowmeter. Two-phase flow experiments, encompassing bubbly to slug flow regimes, were conducted with a water–air mixture.

The simple relation ΔU_TP=ΔU_SP/(1−), relating the flowmeter signal between single-phase flow and two-phase flow, was verified with measurements of the potential difference and the void fraction for a bubbly flow regime. Due to the lack of homogeneity in a real two-phase flow, the discrepancy between the relation and the present measurement increased slightly with increasing void fraction and superficial liquid velocity j_f.

Whereas there is no difference in the shape of the raw signal between single-phase flow and bubbly flow, the signal amplitude for bubbly flow is higher than that for single-phase flow at the same water flow rate, since the passage area of the water flow is reduced. In the case of slug flow, the phase and the amplitude of the flowmeter output show dramatically the flow characteristics around each slug bubble and the position of the slug bubble itself. Therefore, the electromagnetic flowmeter shows a good possibility of being useful for identifying the flow regimes.     

A noninvasive electromagnetic flowmeter

The reliability and reproducibility of peripheral blood flow data obtained by a noninvasive electromagnetic flowmeter were tested using seven male and three female volunteers aged 15-46 years. Each subject was studied under multiple testing conditions in which time, subject's metabolic state, and electrode placement were varied. Each condition was repeated within 1 to 8 weeks to obtain test-retest data. Intraclass reliability coefficients of 0.864-0.998 were obtained on all pulsatile components both within a given measurement sessions and from one day to the next. The size and shape of the waveforms obtained from the data did not significantly differ from one another, thus indicating excellent reproducibility. No significant differences were found between data obtained from the right leg and that obtained from the left. The noninvasive electromagnetic flowmeter was found capable of providing reliable and reproducible data. For data analysis, the second of two consecutive curves seems to be the best choice for clinical assessment.