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Advances in application technology of electromagnetic flowmeter flow measurement
2012-3-13 10:24:59

Low conductivity electromagnetic flowmeter

The electrode of the low-conductivity electromagnetic flowmeter does not come into contact with the liquid to be measured. The large-area electrode is closely attached to the outer wall of the lining. The flow signal is detected by capacitive coupling. It can measure 2 to 3 orders of magnitude lower than traditional meters. × 10-8S / cm liquid, such as pure water, liquid ammonia (not ammonia), glycerol, ethylene glycol, etc., liquids that could not be measured or difficult to measure before, foreign products are also called electrodeless electromagnetic flowmeters. This instrument can still work under the condition that the insulation layer is formed in the lining. If the conventional contact electrode electromagnetic flowmeter is used, the electrode surface will be covered by the insulation layer to make the circuit open and cannot work. This advantage plays a role in expanding the scope of application. , Greater than the role of reducing conductivity.

流量传感器多参数测量 Multi-parameter measurement of electromagnetic flowmeter flow sensor

The so-called multi-parameter measurement is to use the sensing element to sense more than one variable from the measured object according to different physical phenomena, so that the function of the flow sensor (transmitter) is expanded. For example, the Coriolis mass flow meter measures the frequency phase difference of the vibrating tube to obtain the mass flow rate; the density of the vibrating tube resonance frequency is obtained. Or add another sensing element (or sensor) to the flow sensor to measure another variable, expand the function or compensate for another variable affected by other quantities, and improve performance such as measurement accuracy.
1. Differential pressure transmitter, the novel differential pressure transmitter can measure differential pressure, static pressure and temperature at the same time, and calculate the gas pressure and temperature by the calculation unit, or measure the mass flow of gas. This is familiar to people, reducing the number of independent sensors, simplifying pipeline engineering and reducing installation costs; reducing pipeline openings, reducing potential leak points, and improving overall reliability. 2. Coriolis mass flowmeter, Coriolis mass flowmeter uses the phase difference of the vibration frequency of the two half of the measuring tube to be proportional to the mass flow rate to measure the flow rate, and uses the function relationship between the resonance frequency of the measuring tube and the density of the measured medium in the tube to determine Take the density. Coriolis mass flowmeter also derives volume flow rate qv from two basic parameters, mass flow rate qm and density ρ; if the measured liquid is two mixed liquids with a certain density difference, one can also be calculated by density calculation. The concentration of the liquid in the mixture. For example, Jiangsu Oilfield uses Coriolis mass flowmeter to measure the mass flow rate of oil-water mixed liquid after gas-liquid separation at the wellhead. The oil content concentration is measured at the same time as the measurement. The crude oil mass flow rate has been calculated for more than 5 years. Experience. Another example is to measure the concentration of coagulant aluminum sulfate (alum) in the water supply industry, to obtain the total amount of aluminum sulfate trade transfer, to prevent the supplier from deliberately diluting when measuring only the mass flow of the solution. In the process industry, density measurement can also be used to control whether the mixing ratio in the container or the reaction process has reached the required concentration; it can also determine the type of liquid flowing in the pipeline and instruct the flow to the downstream respective piping system [10 22]. 3. Ultrasonic flowmeter, ultrasonic flowmeter uses the physical properties of ultrasonic waves with different speeds in different liquids (for example, the sound velocity of petroleum is 1295m / s, and the water is 1388m / s), and the liquid type in the pipeline is identified while measuring the flow rate. For example, in Europe, an ultrasonic flowmeter is often used to measure the inflow volume when the ship is unloaded and put into storage. At the same time, it is judged whether the liquid being transported is oil or the bottom water of oil tankers. The University of Cranfield in the United Kingdom has tried to use an ultrasonic mass flowmeter for the aviation industry. It is based on the propagation time method of ultrasonic volume flowmeters, and then uses ultrasound to measure the second parameter liquid impedance and density, and calculates the mass flow rate. Water and oil experiments on the prototype prototype show that ± 1% accuracy can be obtained at a flow rate of 1800kg / h and a range of 50: 1.


重视经济效益 Electromagnetic flowmeter values economic benefits

The energy and materials flowing through the flow meter are expensive resources. People pay attention to the overall economic benefits of applying the flow meter, and the economic factors of selecting the flow meter often dominate. The economic benefits of flow meters are divided into three levels: the first level is the loss of overpayment or undercharge caused by meter measurement errors; the second level is the operating costs, including pumping energy costs, periodic calibration costs and maintenance costs; the third level It is the initial installation cost, including the instrument purchase fee, pipeline fittings fee, and engineering commissioning fee. 1. Reduce the loss caused by the measurement error of the instrument. For the instruments used in storage transfer, trade settlement, etc., the user always chooses the instrument with the highest measurement accuracy. The instruments used for critical measurement work are still willing to use even if they are expensive to hundreds of thousands of dollars, because compared to the reduced losses, they are still a fraction. The basic error of the relatively high-precision flow meter 30 years ago was generally (1% to 1.5%) FS, the highest was 0.5% R, and to the present day it is generally (0.5% to 1%) R, the highest is (0.1% to 0.5%) ) R. However, in fact, the accuracy of all aspects of the measurement system should be considered comprehensively. For example, the uncertainty of the standard orifice plate for non-real flow calibration is 1% to 1.5%. If a 0.1% differential pressure transmitter is used, it has little practical significance and is suitable for use. 0.5% is enough! In addition to the use of high-precision instruments for the transmission and transfer of pipeline materials, a dual-meter system with one instrument on each of the sender and receiver is commonly used to check each other. This is often the case even when measuring waste water, because the sewage treatment unit charges constant or even ten times the price of clean domestic and industrial water. 2. Reduce operating costs: In order to reduce the pumping energy consumption of the flow sensor due to pressure loss due to measurement, there is a tendency to use instruments with or without pressure loss or low pressure loss, especially for large-diameter water delivery, regardless of whether the factory water or raw water enters the factory. For financial settlement transfer measurement, there is no pressure loss electromagnetic flow meter and ultrasonic flow meter; flow control flow measurement uses low-pressure loss plug-in meters. The author has tried to calculate a 1m diameter venturi differential pressure flowmeter pumping energy consumption for one year is enough to buy a medium-priced electromagnetic flowmeter. Throttling flowmeters that have been used more and have larger pressure losses have recently developed or valued the application of several low pressure differential pressure generators, such as v-Conen flowmeters and elliptical arc transition flow tubes. Their pressure loss is only 1/20 to 1/2 of the orifice plate. 3. Reduction of the initial installation fee: The initial installation fee of the flow meter should include the purchase cost of the meter itself, engineering costs such as the meter pipeline shut-off valve, and the cost of accessories such as filters and flow regulators. The combined total cost is called TOC (total cost of ownership) abroad. With the increase of demand, the decrease of manufacturing costs and market competition, the overall price of flow meters has slowly declined, but some of them have a large price reduction. For example, Coriolis mass flowmeters have only unique patented products since the late 1970s and early 1980s. The initial stage was expensive. With the equivalent of patents, there are now more than 45 manufacturers worldwide and competition is fierce. Each manufacturer takes measures to reduce prices in order to occupy a larger market share. For example, slightly sacrificing performance and accuracy, reducing some functions and other means, the introduction of economical, foreign economic instrument prices from the original model of 5,000 US dollars to about 3,500 US dollars, and many foreign manufacturers develop ultrasonic testing vortex flowmeters, Its price is also cheaper than traditional meters. Saving on auxiliary setup fees is also an aspect of reducing TOC. In recent years, Japan has canceled the differential pressure flowmeter pressure tube to reduce maintenance work and reduce the initial installation cost. It is quite lively. In recent years, it has introduced a throttling device and differential pressure transmitter to the market to form an integrated direct installation differential pressure flowmeter or The capillary remote differential pressure transmitter replaces the differential pressure flowmeter of the traditional impulse pressure. Some people have conducted investigations in Japan. From 1996 to 1997, nearly 400 new differential pressure meters were used in four new work houses. The three-legged type, integrated direct installation type and capillary remote transmission type are already three-legged, each accounting for one-third.

Installation impact and media parameter impact

The influence of pipeline installation of flow instruments has been valued internationally. Research on the influence of flow obstruction (reduced pipe, reducer, valve, etc.) on the flow measurement of flow velocity distribution distortion and swirling flow, and methods to reduce or eliminate them And equipment (flow straighteners, flow regulators) research and development, has continued to persevere. The research results of more than ten years have been published in academic conferences and professional journals, and some of the results have been adopted by international standards or national standards. In order to amend the national standard ISO 9951 "Measurement of Gas Flow in Closed Pipes-Turbine Flowmeters", the installation conditions are required. The Dutch Gas Federation will conduct three-dimensional bend test on 150 and 300mm gas turbine flowmeters. These research results are Adopted in corresponding standards. Another example is the commentary of the Japanese standard JIS 8766-1989 "Vortex flowmeter flow measurement method", which lists examples of the influence of the vortex flowmeter before and after the bend, reducer, and gate valve are installed with the tube bundle flow straightener; The JIS 7554-1993 "Electromagnetic Flowmeter" commentary also lists examples of the influence of different opening degree gate and butterfly valves, single elbow, flat and three-dimensional double elbow on the electromagnetic flowmeter. The new edition of the "Measuring Engineering Manual" by Miller's in the United States wrote a special chapter on the impact of the instrument. The book brings together the effects of mono and binaural ultrasonic flow meters, turbine flow meters, vortex street flow meters, volumetric flow meters, and Coriolis mass flow meters, and the effects of tube bundle flow straighteners. Research and development to reduce or eliminate the impact of pipeline installations has also made great progress. The draft international standards ISO / CD5167-1 and ISO / CD 5167-2, which are being revised, recommend several types of flow regulators, some of which are included in the standard for the first time. The equipment that mainly reduces the swirling flow is called flow straightener, such as tube bundle type, Etoile type, AMCA type; the equipment that mainly overcomes the distortion of the flow field is called (true flow conditioner), such as NEL (Spearman) and Gallagher and K-Lab Laws Nova 50E. If you want to realize the experimental research on the effects of various choke members and the effects of flow adjustment, the project is huge, the experiments are numerous, and the cost is not loan. No domestic unit has systematically carried out this work. It seems that spending some effort to bring together research results published internationally is a practical and effective method for me.

Foreign users have expressed doubts about the media parameters claimed by the instrument manufacturer, such as temperature, pressure, and viscosity, which have no effect on some flow instruments. They are organized by a consortium to verify this with a third-party research institution. Several test examples are described below. 1. Literature on electromagnetic flowmeters [1] * reported that 20 electromagnetic flowmeters from 8 manufacturers have experienced two and a half years of experiments on liquid temperature, ambient temperature, viscosity effects and liquid conductivity. The data show that these parameters have some effects. It can also be said that it is quite large compared to a meter with 0.2 or 0.5 accuracy. The viscosity of the liquid changes within the range of 5 to 200 mm2 / s, and the average change of the displayed value is 0.7% to 1.6%. The average influence of liquid temperature is (0.08 ~ 0.28)% / 10 ℃. Reference [2] * excerpted several data on the effects of liquid temperature, ambient temperature and viscosity on the long-term stability in this report. 2. Coriolis mass flow meter NEL (British Engineering Laboratory) has made viscosity effects, density effects, water temperature effects, etc. on 8 sets of 25mm caliber instruments from different manufacturers. Some instruments have very small effects and some have obvious effects. Can water-calibrated meters be used for gases? What is the difference? Fisher Rosemount said that the air calibration data for the two ELITE CMF 300 meters at the plant was -0.41% different from the factory water acceptance data. PIB (German Institute of Physics and Technology) calibrated 15mm instrument with 20MPa natural gas, the error is ± 0.7%. China Metrology Institute uses a pressure of about 1 MPa to calibrate an LZKI-2 instrument with a caliber of 6 mm. When the flow rate is about 10 kg / h, the difference is -0.59% compared with the water calibration.