了解流量设备号称企业的“点钞器”，选择合理价格精度的流量测量设备在企业经营和设备采购中都有重要的地位，虽然物资采购部门对设备的选型和使用没有太多发言权，但是设备的不同类型和价格有着很大的关系，在成本经济的今天，采取积极的态度虚心学习设备专业知识，对所采购设备有清楚的认识，就可以对所采购设备选型和使用提出中肯的建议，会大大节省采购费用，对公司的整体效益作出贡献。 According to the double-needle pressure gauge, we know that the flow equipment is called the "counter of money" of the enterprise. Choosing the flow measurement equipment with reasonable price accuracy plays an important role in the business operation and equipment procurement. Although the material procurement department does not have the equipment selection and use, Too much say, but the different types and prices of the equipment have a great relationship. In today's cost-effective world, take a positive attitude and learn the equipment professional knowledge with an open mind. With a clear understanding of the equipment purchased, you can choose the equipment you purchase. Proposed suggestions on the type and use will greatly save procurement costs and contribute to the company's overall efficiency. This article attempts to give a brief introduction to the professional knowledge of traffic equipment, and make a rough summary of the problems encountered in procurement. I hope that it will be inspired when encountering similar product procurement.
Keywords: flow equipment selection, procurement control
First, the basic knowledge of traffic equipment:
The classification of flow equipment, according to the measurement principle of flow equipment, can be divided into: volumetric flowmeter, speed flowmeter, target flowmeter, electromagnetic flowmeter, vortex flowmeter, rotor flowmeter, differential pressure flowmeter, ultrasonic flowmeter , Mass flow meter, etc.
1. Rotor flowmeter
Float flowmeter, also known as rotor flowmeter, is a type of variable area flowmeter. In a vertical cone tube that expands from bottom to top, the gravity of the float with a circular cross section is borne by liquid power. Freely rise and fall inside the cone. It moves up and down under the action of flow velocity and buoyancy, and after balancing with the weight of the float, it is transmitted to the dial to indicate the flow through magnetic coupling. Generally divided into glass and metal rotor flowmeters. Metal rotor flowmeters are the most commonly used in the industry. For corrosive mediums with small diameters, glass materials are usually used. Due to the fragility of glass materials, the key control point is also available with all titanium and other precious metals. . There are many domestic manufacturers of rotor flowmeters, mainly including Chengde Kroni (using German Cologne technology), Kaifeng Instrument Factory, Chongqing Chuanyi, and Changzhou Chengfeng all produce rotor flowmeters. Due to their high accuracy and good repeatability, It is widely used in small pipe diameter (≤ 200MM) flow detection.
2. Volumetric flowmeter
的容积式流量计是通过测定壳体和转子之间形成的计量容积来测量流体的体积流量。 The volumetric flowmeter of the double needle pressure gauge measures the volume flow of a fluid by measuring the measuring volume formed between the housing and the rotor. According to the structure of the rotor, volumetric flowmeters include waist-wheel type, scraper type, and oval gear type. Volumetric flow meters are characterized by high measurement accuracy, some can reach 0.2%; simple and reliable structure; wide applicability; high temperature and pressure resistance; installation conditions are not high. Widely used in the measurement of crude oil and other oil products. However, because of gear transmission, the block of the pipeline is the biggest hidden danger. It is necessary to install a filter in front of the equipment, which has a limited life and often requires maintenance. The main domestic production units are: Kaifeng Instrument Factory, Anhui Instrument Factory, etc.
3, differential pressure flowmeter
The differential pressure flowmeter is a measuring device with a long history and complete experimental data. It is a kind of flow meter that displays the flow rate by measuring the static pressure difference generated by the fluid flowing through the throttling device. The most basic configuration is composed of a throttling device, a differential pressure signal line and a differential pressure gauge. The most commonly used in the industry is that the throttle device is a "standard throttle device" that has been standardized. For example, standard orifice plate, nozzle, venturi nozzle, venturi tube. Now the throttling device, especially the nozzle flow measurement, is heading towards the integration direction, integrating the high-precision differential pressure transmitter and temperature compensation with the nozzle, which greatly improves the accuracy. Pitot tube technology enables online calibration of the throttling device. At present, some non-standard throttling devices are also used in industrial measurement, such as double orifice plate, round orifice plate, annular orifice plate, etc. These instruments generally require real-flow calibration. The structure of the standard throttling device is relatively simple, but because of its high requirements for dimensional tolerance, shape and position tolerance, the technical difficulty of processing is relatively high. Taking the standard orifice plate as an example, it belongs to ultra-thin plate-like parts, which is prone to deformation during processing. Large orifice plates are also liable to deform during use and affect accuracy. The pressure-receiving hole of the throttling device is generally not too large, and it will also deform during use and affect the measurement accuracy. Due to the friction of the fluid on the standard orifice plate during use, it will also cause the measurement-related structural elements (such as acute angles) to wear and reduce the measurement accuracy.
Although the development of differential pressure flowmeters is relatively early, with the continuous improvement and development of other various types of flow meters, and the continuous development of industrial development requirements for flow measurement, the status of differential pressure flowmeters in industrial measurement has been partially Replaced by advanced, high-precision, convenient flow meters.
4, electromagnetic flowmeter
The electromagnetic flowmeter is based on the principle of Faraday's electromagnetic induction. It is an instrument for measuring the volumetric flow of conductive liquids. According to Faraday's law of electromagnetic induction, when a conductive body moves in a magnetic field to cut magnetic field lines, an induced voltage is generated in the conductor. In the magnetic field, the speed of motion perpendicular to the magnetic field is proportional to the flow rate.
Electromagnetic flowmeter and selection principle: 1), the liquid to be measured must be conductive liquid or slurry; 2), the caliber and range, preferably the normal range exceeds half of the full range, and the flow rate is between 2 and 4 meters; 3 ), The use pressure must be less than the pressure resistance of the flowmeter; 4), different temperatures and corrosive media choose different lining materials and electrode materials.
The measurement accuracy of the electromagnetic flowmeter is based on the fact that the liquid is filled in the pipeline. The problem of measuring air in the pipeline has not been well solved.
The converter of the electromagnetic flow meter is its core component, which directly affects the accuracy of the measurement. At present, domestically produced converters fail to meet the requirements for various reasons, and are basically monopolized by foreign brands. It is small and reduces energy consumption. It is only related to the average speed of the measured fluid and has a wide measurement range. It can be used to measure other media after calibration with water. No correction is required. It is most suitable for use as a settlement measurement device. 对其成本也得到了降低，但整体价格特别是大管径的价格仍较高，因此在流量仪表的采购中有重要的地位。 Due to the continuous improvement of technology and process materials, the continuous improvement of stability, linearity, accuracy and life and the continuous expansion of pipe diameter, the measurement of solid-liquid two-phase media uses replaceable electrodes and scraper electrodes to solve the problem. The measurement problems of high pressure (32MPA), corrosion-resistant (anti-acid, alkali lining) media, and the continuous expansion of the caliber (up to 3200MM caliber), the continuous increase of life (generally greater than 10 years), electromagnetic flowmeters are getting Widely used, the cost of double needle pressure gauges has also been reduced, but the overall price, especially the price of large diameter pipes, is still high, so it has an important position in the purchase of flow meters.