枣阳Principle of selection of mass flowmeter

1, according to the type of measured flow meter structure: Coriolis force type mass flowmeter measuring tube has many forms, need to be considered according to the type of measured medium selection. In principle, the pure liquid with low viscosity has no requirement on the shape of the measuring tube. When measuring the liquid containing a small amount of bubbles, containing solid particles of the slurry and high viscosity liquid, should choose the measurement tube is not easy to accumulate bubbles or solid particles, the inner wall is not easy to adhere to the shape of the medium; If used in the food industry, the measuring tube should be easy to clean.

2, the safety principle: when measuring corrosive fluid, attention should be paid to the corrosion resistance of the measuring tube, and the sensor shell should also have a certain corrosion resistance. In case the test tube is broken, safety precautions should be taken before treatment. The corrosiveness of different media is different, and the anticorrosion objects of different materials are different, so attention should be paid to different treatment. The wear resistance of the measuring tube should be considered when the measuring medium is abraded. When the process pressure is high, the pressure resistance level of the sensor should be paid attention to so as not to damage the measuring tube. When the medium temperature is high, the temperature range of the sensor should be considered to avoid damage to the detection element. If the selected flowmeter is used in dangerous areas or harsh environment, special attention should be paid to the explosion-proof flowmeter, protection level should meet the requirements of safety standards.

3, flow range: Considering the flow range should comply with two principles: First, the flow range of Tianchen Borui flowmeter should be able to cover the process flow range of the measured medium. Secondly, the flow rate of common process should fall within the economic flow range of the flowmeter. The so-called economic flow range has two meanings here: First, because Coriolis force type mass flowmeter, its zero stability has a great impact on the measurement accuracy of the lower limit flow. The closer it is to the upper limit of flow, the less influence of zero stability on accuracy. Therefore, the range above 1/3 of the upper limit of flow meter can be called the economic flow range of accuracy. Second, for the same type of flowmeter, if there are several diameters of measurable flow range can cover the process flow range, the choice of smaller diameter flowmeter can obviously save money, more economic. But this kind of economy is not absolute, if the pursuit of the use of flow rate is close to the upper limit of flow meter in the range, is bound to cause the measurement tube medium velocity is too high, the negative effect will be pressure loss is too large and unsafe increase. Some inflammable and explosive medium, if the velocity is too high, easy to cause deflagration due to friction electrostatic. Therefore, the media should be careful not to exceed the safe flow rate.

4. Accuracy: The requirement of accuracy level should be determined according to the measurement object and purpose, and attention should be paid to the calculation method of product accuracy level and the conditions or constraints of the use of the level. Generally speaking, Coriolis force type mass flowmeters use the percentage of the flow reading with zero stability to express the accuracy level, and some products use different flow sections corresponding to different error limits, and some products use the percentage of the full range to express the error level in the low flow section. For Coriolis force type mass flowmeter, the following two points should be paid attention to when considering its accuracy class: First, due to the particularity of the calculation method of accuracy class of this kind of flowmeter, some products have given a very high accuracy class, and the zero drift value is also very high, thus increasing its allowable error limit; The second is that some products give high accuracy levels at low zero drifts, but it requires nearly harsh installation conditions that can only be done in the laboratory. Due to the widespread vibration and the limitation of installation site, it is difficult to meet such installation conditions to achieve the theoretical effect. Neither of these "high accuracy" levels is adequate. In the case of achieving the measurement accuracy requirements, we should consider the price and other factors, do not blindly pursue too high accuracy level. On the other hand, in principle, the measurement characteristics of Coriolis force mass flowmeter are not affected by the temperature and pressure of the medium, but in fact, due to the limitations of manufacturing process and material properties, the above factors have a certain impact on the characteristics of the flowmeter. The ex-factory verification conditions of flowmeters are generally fixed, but the use conditions are ever-changing. If the use conditions are too different from the verification conditions, the influence of these uncertain factors must be considered in the selection. At present, the specific degree of influence of these factors on measurement results and the correction method have been obtained by derivation and experiment of some products. When the flowmeter is elected to konw dense measurement, it should be corrected.

5, pressure loss: in the field measurement, there are always certain requirements for the pressure loss of the flowmeter. When the density, viscosity and flow of the medium are determined, the size of the pressure loss of the flowmeter depends on its structure, the Coriolis force type mass flowmeter is dependent on the diameter, flow area and the shape of the measuring tube; When the structure of the sensor is determined, the greater the flow rate, the greater the pressure loss. In the selection of pressure loss calculation, the following points should be fully considered: flow in the process line and allowable pressure loss; Whether the sensor meets the requirement of measurement accuracy under the condition of allowable pressure loss; The influence of viscosity and density of process fluid on pressure loss; In application, the pressure should avoid excessive vaporization of ambassador liquid. When other conditions are the same, the flowmeter with less pressure loss should be selected.

6, the consideration of other performance factors: one is to consider the additional measurement performance of the flowmeter, such as Coriolis force type mass flowmeter measurement medium temperature, density accuracy; The second is to consider the mass flowmeter volume, weight and special cable restrictions and other factors affecting the installation.

7, performance price is a basic principle of selection. In the specific application, in addition to considering the good performance and low price, there is often a preference for the diversity of functions, believing that the more functions, the better. In fact, as a mass flowmeter, its main purpose is to detect the mass flow of fluid. Although transmitters generally use microcomputer technology and (super) large-scale integrated circuits, can achieve more diversified functions, but this is bound to increase the cost of manufacturing, and some of the functions in the specific application may not be necessary and practical. On the other hand, from the reliability theory, the more complex the performance and structure, the lower the reliability. Therefore, from the actual need to consider the performance of the flowmeter price is the correct principle. Think about performance versus price, which is usually what we call value for money. As a mass flowmeter, this "value" is not only reflected in the function and performance, but also reflected in the sales and service of the product. With the progress of technology and their own continuous efforts, the manufacturing level gap between the manufacturers is narrowing day by day, a unique become each other's complementarity. According to the above selection principles, sometimes a measuring point can be selected several brands of available products, then should choose the strength of the Guangjia flowmeter. Investigate the strength of the manufacturer, not only to see its manufacturing level, production capacity, but also to investigate its service level. This service not only represents what is commonly referred to as after-sales service, but also includes pre-sale and in-sale services. In addition to introducing product performance, offering quotation, promising service and other common practices, pre-training users so that they can master installation and debugging and some common troubleshooting methods, until guiding installation and helping debugging. The length of delivery cycle, the specific guarantee measures for product quality, the time of free service, the response speed in case of failure, the processing level, the protection of spare parts, and even the service attitude of maintenance personnel, all represent the service level of the manufacturer.

The above selection principles sometimes restrict each other. In the actual selection work, we should start from the actual needs of the site and consider comprehensively. According to the different characteristics of different occasions, some emphasis. As long as the selection work is done, the instrument can be used well. It can be said that the correct selection is the premise of satisfactory use.