Flow is one of the important measurement parameters in chemical production. 电磁流量计 都能做到测量稳定、可靠、精度高、易维护。 Regarding the measurement of conductive liquid flow, regardless of the purpose of monitoring or metering, the electromagnetic flowmeter can achieve stable, reliable, high accuracy and easy maintenance. In the selection and use of the meter, the author summarizes some points for practical reference based on practical applications.
DXLDE 系列 电磁流量计 的工作原理 1. The working principle of DXLDE series electromagnetic flowmeter
系列 电磁流量计 的基本原理是法拉第电磁感应定律，即导体在磁场中切割磁力运动时在其两端产生感应电动势。 The basic principle of the DXLDE series electromagnetic flowmeter is Faraday's law of electromagnetic induction, that is, when a conductor cuts magnetic force in a magnetic field, it induces electromotive force at both ends. 电磁流量计 测量管内的导电介质相当于法拉第试验中的导电金属杆，上下两端的两个电磁线圈产生恒定磁场。 The conductive medium in the measuring tube of the electromagnetic flowmeter is equivalent to the conductive metal rod in the Faraday test, and the two electromagnetic coils at the upper and lower ends generate a constant magnetic field. When a conductive medium flows through, an induced potential is generated. The induced voltage is measured by two electrodes inside the pipe. ( 橡胶，特氟隆等 ) 实现流体与测量电极的电磁隔离。 The measuring pipe is electromagnetically isolated from the measuring electrode by a non-conductive inner lining ( rubber, Teflon, etc. ) .
系列 电磁流量计 由流量传感器和变送器两大部分组成。 DXLDE series electromagnetic flowmeter consists of two parts: flow sensor and transmitter. The sensor measuring tube is provided with an excitation coil above and below, and a magnetic field is generated after the excitation current is passed through the measuring tube. A pair of electrodes are mounted on the inner wall of the measuring tube to contact the liquid, and the induced potential is led to the transmitter. The excitation current is provided by the transmitter.
2. 系列 电磁流量计 的特点 Features of DXLDE series electromagnetic flowmeter
结构简单， DXLDE 系列 电磁流量计 的测量管道是一段无阻流扰动件或节流件的光滑直管，不易发生堵塞、磨损等问题。 1) The structure is simple. The measuring pipe of the DXLDE series electromagnetic flowmeter is a smooth straight pipe without obstruction or throttling parts. It is not easy to cause problems such as blockage and wear. ， DXLDE 系列 电磁流量计 特别适用于含固体颗粒或纤维的液固两相流体，如纸浆、泥浆、矿浆、煤水浆和污水等。 Therefore , the DXLDE series electromagnetic flowmeter is particularly suitable for liquid-solid two-phase fluids containing solid particles or fibers, such as pulp, mud, mineral pulp, coal water slurry and sewage.
由于没有节流件，仪表几乎无压力损失，仅消耗 10 ～ 20W 的电功率，这点与节流的差压式流量计相比，其节能效果成为 电磁流量计 发展的一大优势。 2) Because there is no throttle, the instrument has almost no pressure loss, and only consumes 10 to 20W of electrical power. Compared with the throttled differential pressure flowmeter, its energy saving effect has become a major advantage in the development of electromagnetic flowmeters .
DXLDE 系列 电磁流量计 所得的体积流量，实际上不受流体密度、粘度、温度、压力、雷诺数以及在一定范围内电导率变化的影响。 3) The volume flow obtained by the DXLDE series electromagnetic flowmeter is actually not affected by fluid density, viscosity, temperature, pressure, Reynolds number, and conductivity change within a certain range.
DXLDE 系列 电磁流量计 测量范围很大，通常为 20 ∶ 1 ～ 50 ∶ 1 ，每个量程又可从 2% ～ 100% 线性测量， 电磁流量计 的测量范围可涵盖紊流和层流两种速度分布状态，这是其他流量计不能与之相比拟的。 4) DXLDE series electromagnetic flowmeter has a large measurement range, usually 20 : 1 to 50 : 1 , each range can be linearly measured from 2% to 100% . The measurement range of electromagnetic flowmeter can cover both turbulence and laminar flow. This kind of speed distribution state, which is unmatched by other flow meters.
测量原理是线性的，测量精确度高，反应速度快，可测脉动流量和快速累积总量，可测正反双向流量，传感器前后直管段要求低。 5) The measurement principle is linear, high measurement accuracy, fast response, can measure pulsating flow and fast total accumulation, can measure forward and reverse bidirectional flow, and requires low straight pipe sections before and after the sensor.
耐腐蚀性能好，使用可靠，维护方便，寿命长。 6) Good corrosion resistance, reliable use, convenient maintenance and long life.
电磁流量计 不能测量电导率很低的液体，如石油制品和有机溶剂等；不能测量气体、蒸汽、和含有较多较大气泡的液体；受衬里材料和电极绝缘材料的温度限制，不能测量较高温度的液体。 However, electromagnetic flowmeters cannot measure liquids with very low electrical conductivity, such as petroleum products and organic solvents; they cannot measure gases, vapors, and liquids with large bubbles; they are limited by the temperature of the lining material and the electrode insulation material. Measure higher temperature liquids.
3 系列 电磁流量计 的选型考虑要点 Selection considerations of DXLDE series electromagnetic flowmeter
电磁流量计 的特点，重点要求考虑四个方面的因素，即仪表性能、流量特性、安装条件和环境条件。 In the design of petrochemical industry, there are many factors to consider when choosing a suitable flow meter. Specific to the characteristics of electromagnetic flowmeters , there are four factors that need to be considered, namely meter performance, flow characteristics, installation conditions and environmental conditions.
仪表性能 a. Instrument performance
电磁流量计 的功能差别也很大，简单的就只是测量单向流量，只输出模拟信号带动后位仪表；多功能仪表有测双向流、量程切换、上下限流量报警、空管和电源切断报警、小信号切除、流量显示和总量计算、自动核对和故障自诊断、与上位机通信和运动组态等。 The functions of electromagnetic flowmeters on the market are also very different. The simple one is to measure the unidirectional flow and only output the analog signal to drive the rear instrument. The multifunctional instrument has two-way flow measurement, range switching, upper and lower limit flow alarm, air pipe and power supply. Cut off alarm, small signal removal, flow display and total calculation, automatic check and fault self-diagnosis, communication with upper computer and motion configuration, etc. (ASIC) ，以连接 HART 协议系统、 PROFTBUS 、 Modbus 、 FF 现场总线等。 The serial digital communication function of some models of instruments can choose a variety of communication interfaces and application-specific chips (ASIC) to connect HART protocol system, PROFTBUS , Modbus , FF field bus, etc.
系列 电磁流量计 的口径范围比其他品种流量仪表宽，如东祥仪表提供 W 、 P 、 H 三种类型的传感器，分别应用于水和污水行业 (W 型 ) ，化工、食品行业 (P 型 ) ，食品、制药行业 (H 型 ) ，口径范围从 2 毫米到 3 米。 DXLDE series electromagnetic flowmeters have a wider caliber range than other types of flow meters. For example, Dongxiang meters provide three types of sensors: W , P , and H , which are respectively used in the water and sewage industry (W type ) , chemical industry, and food industry (P type). ) , Food, pharmaceutical industry (H type ) , caliber range from 2 mm to 3 meters. 10 、 50 、 23 、 53 多种选择， 10 针对于水行业开发的经济型，分为普通型、增强型、两线制。 Transmitter can provide more than 10 , 50 , 23 , 53 choices, 10 for the economic development of the water industry, divided into ordinary, enhanced, two-wire system. 0.5% ， 0.2% 等选择。 Accuracy can be selected from 0.5% and 0.2% . Can measure forward and reverse bi-directional flow, also can measure pulsating flow.
2m/s ，最好提高到 3 ～ 4m/s 或以上，起到自清洗、防止粘附沉积等作用。 For easy adhesion, deposition, scaling and other media, the flow rate should be not less than 2m / s , it is best to increase to 3 to 4m / s or more, to perform self-cleaning and prevent adhesion and deposition. 2 ～ 3m/s ，以降低衬里和电极的磨损。 For abrasive fluids such as slurry, the flow rate should be less than 2 to 3 m / s to reduce the wear of the lining and electrodes. “ 材料手册 ” ，如《自控常用材料器件手册》。 The choice of lining, electrode, and grounding ring materials is also critical. You can refer to the " Materials Manual " for different media , such as the "Automated Common Materials and Devices Manual".
流体特性 b. fluid characteristics
电磁流量计 的前提是被测液体必须是导电的，不能低于阈值 ( 即下限值 ) 。 The premise of using an electromagnetic flowmeter is that the measured liquid must be conductive and cannot be lower than the threshold value ( that is, the lower limit value ) . 电磁流量计 的阈值在 10-4 ～ (5×10-6)S/cm 之间，视型号而异。 If the conductivity is lower than the threshold value, a measurement error will occur until it cannot be used. It can be measured even if it exceeds the threshold value. The indication error does not change much. The threshold value of the general-purpose electromagnetic flowmeter is 10-4 ～ (5 × 10-6) S / cm. Depending on the model. It also depends on the length of the flow signal line and its distributed capacitance between the sensor and the converter. The manufacturer's instruction manual usually specifies the length of the signal line corresponding to the conductivity.
10-4S/cm ，酸、碱、盐液的电导率在 10-4 ～ 10-1S/cm 之间，使用不存在问题，低度蒸馏水为 10-5S/cm 也不存在问题。 The conductivity of industrial water and its aqueous solution is greater than 10-4S / cm , and the conductivity of acids, alkalis, and salts is between 10-4 to 10-1S / cm. There is no problem in use. Low-distilled water is 10-5S / cm . cm is not a problem. From the information, we found that some pure liquids or aqueous solutions have low electrical conductivity and are considered unusable. However, in practice, we will encounter examples that can be used because they contain impurities. Such impurities are beneficial to increase the conductivity. For the aqueous solution, the conductivity in the data is measured in the laboratory with pure water ratio. The actual aqueous solution may be used with industrial water ratio. The conductivity will be higher than that found, which is also beneficial to flow measurement.
安装条件 c. Installation conditions
1 ）按 电磁流量计 自身的转换器与传感器组装方式分类，有分离型和一体型两种。 ( 1 ) According to the assembly method of the converter and sensor of the electromagnetic flowmeter , there are two types: separated type and integrated type. IP68( 防尘防潜水级 ) ，如果安装在地上，建议选择 IP67( 防尘防溅水级 ) 。 For example, in the sewage plant, large-caliber flowmeter sensors are mostly installed underground, so it is recommended to choose IP68 ( dust-proof and submersible-grade ) . If installed on the ground, it is recommended to choose IP67 ( dust-proof and splash-proof ) . The small caliber is more integrated. 电磁流量计 对安装场所要求有： a. 测量混合相流体时，选择不会引起相分离的场所；测量双组分液体时，避免装在混合尚未均匀的下游；测量化学反应管道时，要装在反应充分完成段的下游；尽量满足前后直管段分别不小于 5D 和 2D ； Generally, the electromagnetic flowmeter requires the installation place to be: a. When measuring mixed-phase fluid, choose a place that will not cause phase separation; When measuring two-component liquids, avoid installing in the downstream where the mixture is not uniform; When measuring chemical reaction pipelines, Installed downstream of the fully completed reaction section; try to satisfy the straight pipe sections at the front and back of not less than 5D and 2D , respectively ;
2 ）尽可能避免测量管内变成负压； ( 2 ) Avoid negative pressure in the measuring tube as much as possible;
3 ） . 选择震动小的场所，特别对一体型仪表； ( 3 ) Choose a place with small vibration, especially for integrated instruments;
4 ）避免附近有大电机、大变压器等，以免引起电磁场干扰； ( 4 ) Avoid having large motors, transformers, etc. nearby, so as not to cause electromagnetic field interference;
5 ）易于实现传感器单独接地的场所； ( 5 ) Places where it is easy to achieve separate grounding of the sensors;
尽可能避开周围环境有高浓度腐蚀性气体； (6) Avoid high concentrations of corrosive gases in the surrounding environment as much as possible;
尽可能避免受阳光直照 (7) Avoid direct sunlight as much as possible
环境条件 d. environmental conditions
GB3836.1 《爆炸性环境电气设备通用要求》的规定，选择适应使用场所环境的气氛、爆炸性混合物的分级分组、设备类型以及其他安全规则或标准的仪表。 General instruments used in explosive hazardous environments should be in accordance with the standard GB3836.1 "General Requirements for Electrical Equipment in Explosive Environments", and choose the instruments that are suitable for the atmosphere of the place of use, the classification of explosive mixtures, the type of equipment, and other safety rules or standards. 电磁流量计 选型的考虑要点。 In addition, the external magnetic field, electrical interference, ambient temperature and humidity are also important considerations in the selection of electromagnetic flowmeters .
使用方便，维护量小，主要是电极的清洗和更换，也有无电极型的 电磁流量计 几乎无需维护。 The electromagnetic flowmeter is easy to use and requires little maintenance. It is mainly the cleaning and replacement of electrodes. There are also electrodeless electromagnetic flowmeters that require almost no maintenance. 电磁流量计 定期进行在线标定和检查也是非常必要的。 Of course, regular online calibration and inspection of the electromagnetic flowmeter is also very necessary. 电磁流量计 性能、特点有了全面深入的了解，有了应付各种工况的策略， 电磁流量计 一定会成为化工测量中的得力助手。 As long as you have a comprehensive and in-depth understanding of the performance and characteristics of electromagnetic flowmeters and strategies to cope with various working conditions, electromagnetic flowmeters will surely become effective assistants in chemical measurement.