Product Application Overview: The fluid flow of industrial drainage is natural flow, large flow, non-full pipe and free water surface, and it is difficult to measure the ground. In the past, the traditional trough type flowmeter was used, which not only has lower precision, but also brings large water flow loss. At the same time, it also has certain requirements on the gradient of the upstream channel and the downstream water depth. When the conditions are not met, the measurement accuracy will decrease, sometimes It is not even possible to make measurements. If you use an electromagnetic flowmeter to measure the effluent, you will need to build additional rams and slabs to ensure full pipe. These additional installation costs often exceed the cost of the flowmeter itself, especially for large diameter pipes, and have increased The possibility of pipe blockage. With the continuous development of measurement technology, both electromagnetic and ultrasonic technologies can measure the flow of non-full pipe fluid. Since the introduction of electromagnetic flowmeters , its technology has matured and it has been widely used in many places in industrial production sites. Since the measurement process of electromagnetic flowmeters is not affected by factors such as temperature, viscosity and density of the measured medium, it has a fast measuring speed. High precision, wide measuring aperture, good linearity of output, no contact with the measured medium, corrosion resistance, wear resistance, low fluid pressure loss, etc., so it is widely used in the measurement of paper pulp, additives, water and other fluids in paper mills. However, electromagnetic flowmeters also have their shortcomings. The output of the sensor has a small induced electromotive force and is susceptible to external electromagnetic interference. The situation on the spot is very different. It is impossible to meet the standard requirements in every measurement environment. Therefore, how to improve the electromagnetic flowmeter The electromagnetic compatibility, so that it can be used normally in a harsh electromagnetic environment is a problem that must be considered in the design of electromagnetic flowmeters. Taking the ADMAGAE series electromagnetic flowmeter of Yokogawa as an example, this paper introduces the use of electromagnetic flowmeter and analyzes its electromagnetic compatibility (EMC) in combination with the author's engineering practice. This paper introduces the method of setting and configuring the electromagnetic flowmeter parameters by using the panel and the intelligent terminal, and improving the electromagnetic compatibility technology of the electromagnetic flowmeter. The interference sources of electromagnetic flowmeter mainly include power frequency electromagnetic interference, fluid electrochemical interference noise and power supply interference noise. At present, electromagnetic flowmeters mainly use low frequency or dual frequency rectangular wave excitation technology, synchronous sampling technology, input protection, grounding technology, etc. to reduce interference. Practical applications show that these technologies have better anti-interference effects. 1 Working principle of electromagnetic flowmeter The operation of the electromagnetic flowmeter is based on the law of electromagnetic induction, that is, when a conductor moves in an electromagnetic field and the direction of motion is perpendicular to the electromagnetic field, an induced electromotive force is generated, and the direction of the induced electromotive force generated is perpendicular to the direction of the movement of the conductor and the movement of the electromagnetic field. The magnitude of the induced electromotive force is proportional to the speed of movement of the conductor and the magnetic induction of the magnetic field. When the conductive fluid passes through a tube having an inner diameter of D (m) at an average flow velocity V (m/s), if a magnetic field having a magnetic induction of B (T) exists in the tube, a direction perpendicular to the magnetic field is generated and Electromotive force E in the direction of fluid flow: E = DVB (V) (1) The volume flow Q is: Q = πD2 V/4 (m3 / s) (2) Substituting equation (2) into equation (1) and processing it: E=(4B/πD)×Q (V) (3) If B and D are constants, then from equation (3), E and Q is proportional. The electromagnetic flow converter amplifies and converts the electromotive force E into a standard 4 to 20 mA signal or pulse signal as a corresponding flow signal output. 2 electromagnetic flowmeter parameter setting method and configuration There are two ways to set the parameters of the flowmeter (configuration). One is to use the buttons on the display panel, and the other is to use the handheld smart terminal. 2.1 Using the Panel for Parameter Setting The symbols commonly used on the ADMAGAE series of electromagnetic flowmeter panels are: (1) RED (red) does not illuminate during normal operation, and flashes when there is an alarm; (2) The delimiter delimiter uses the colon ":" to indicate that the displayed data is in the state to be set; (3) The unit display shows the flow unit; (4) Display data shows the type of flow data, setting data and alarms; (5) The decimal point indicates the decimal point in the data; (6) Set keys These keys are used to change the type of data display and setting data. There are three types of data display types: flow data display mode, setting mode, and alarm display mode. 2.1.1 Traffic data display mode The flow data display mode indicates the instantaneous flow value and the cumulative flow value, and ADMAGAE can display 12 types of flow data. Enter the flow display mode and use the “d1†parameter to change the display item. For detailed settings, refer to the flowmeter user manual. 2.1.2 Setting mode The setting mode is used to check the parameter contents and rewrite the data. This mode can be called up from the normal operating mode by pressing the "SET" button. 2.1.3 Alarm display mode When an alarm occurs, the alarm mode replaces the current mode to display the type of alarm that occurred, but this happens only when the parameter number is changed in the current flow display mode or setting mode (when the data item is being processed, Display alarm). 2.2 BT smart terminal settings A meter with intelligent communication function can communicate with the smart terminal. Yokogawa's intelligent terminals include BT100, BT200 and other models, referred to as BT intelligent terminals. They use the BRAIN protocol to superimpose a ±2 mA, 2.4 kHz modulated signal on an analog signal of 4 to 20 mA for signal transmission. Since the modulated signal is an alternating current signal, the superposition does not affect the value of the analog signal. There are two ways to connect the BT intelligent terminal to the flowmeter: one is directly connected to the BT terminal under the flowmeter end cover. This method is suitable for on-site debugging or the flowmeter does not have the intelligent communication function; the second is with 4~ 20 mA DC signal line connection, BT intelligent terminal can be connected anywhere from the control cabinet to the flow meter signal line, the distance can be up to 2 km, as long as the load resistance of the whole circuit is between 250 and 750 ,, it can be reliable. Ground communication. In this way, the operator does not have to go to the site, and the flow meter can be set and monitored online in the control room, which is a way of using more. The BT intelligent terminal adopts menu operation, which can display and modify various parameters of the electromagnetic flowmeter at any time. The basic operations include flowmeter self-test, range adjustment, display mode setting, and alarm setting. 2.3 Electromagnetic flowmeter data setting and configuration The electromagnetic flowmeter calculates a volume flow rate based on a small electromotive force corresponding to the fluid flow rate and outputs a signal of 4 to 20 mA. In order to ensure the correct signal, three parameters of path, flow range and meter factor must be set. Among the three parameters, the path and meter factor are set well before the instrument leaves the factory, so the user cannot set this. Two parameters. The user can also set the flow range before the instrument leaves the factory. This setting can only be reset when the user requests to change the range. 3 Electromagnetic compatibility analysis The operation of the electromagnetic flowmeter is based on the law of electromagnetic induction. The induced electromotive force generated proportional to the measured flow is usually small, and is highly susceptible to external electromagnetic interference. The electromagnetic interference generated by itself is small, so the electromagnetic flowmeter is electromagnetically compatible. Sex is mainly reflected in how it works in a harsh electromagnetic environment. In the harsh electromagnetic environment, electromagnetic coupling electrostatic induction is the main source of electromagnetic flowmeter interference noise; the electrochemical interference noise generated by the measured fluid medium characteristics is the second source of electromagnetic flowmeter interference noise; the electromagnetic flowmeter power supply voltage and Power supply interference noise such as frequency fluctuations is the third source of electromagnetic flowmeter interference noise. In order to meet the EMC requirements of the instrument, the intelligent electromagnetic flowmeter adopts hardware and software anti-interference technology [1] to improve the anti-interference ability of the electromagnetic flowmeter. 3.1 Characteristics of power frequency interference noise and anti-interference technology of electromagnetic flowmeter The power frequency interference noise is firstly formed by the electromagnetic coupling of the electromagnetic flowmeter excitation coil and the input circuit of the fluid, electrode and amplifier. The second is the power frequency common mode interference of the electromagnetic flowmeter working site, and the third is the power frequency string introduced by the power supply. Mode interference, etc., the physical mechanism produced by them is the principle of electromagnetic induction. The power frequency interference generated by the electromagnetic winding of the electromagnetic flowmeter and the electromagnetic coupling of the fluid, electrode and amplifier input circuit has great influence on the operation of the electromagnetic flowmeter, and its performance and characteristics are different under different excitation technologies, so anti-interference measures are also adopted. different. Under the excitation magnetic field of power frequency sine wave, the electromagnetic coupling power frequency interference noise is expressed as orthogonal interference, also known as transformer potential. The characteristic is that the interference noise amplitude is proportional to the power frequency sine wave excitation frequency, and the phase lag flow signal The potential is 90°, and the amplitude is several orders of magnitude larger than the flow signal potential [2]. DC excitation, low frequency rectangular wave excitation and dual-frequency rectangular wave excitation technology can basically eliminate the influence of orthogonal interference. Two common interferences, power frequency common mode interference and power frequency series mode interference, are mainly caused by electromagnetic shielding defects, distributed capacitive coupling, poor grounding of electromagnetic flowmeter, etc. The electromagnetic flowmeter adopts input protection technology and high input impedance. High common-mode rejection is superior to bootstrap preamplifier technology and repetitive grounding technology to improve resistance to power frequency interference. The ADMAGAE series of electromagnetic flowmeters are equipped with a grounding ring. The function is to establish a liquid ground by contacting the liquid, ensuring that the reference potential is the same as the liquid being measured and protecting the flowmeter lining. 3.2 Characteristics of Electrochemical Interference Noise and Anti-interference Technology of Electromagnetic Flowmeter 3.2.1 Characteristics of electrochemical interference noise (1) Electrochemical polarization potential interference is caused by polarization of the electrolyte on the surface of the electrode due to the polarity of the electrode induced electromotive force at the polarities of the electrodes. Although the use of positive and negative alternating excitation magnetic fields can significantly reduce the magnitude of the polarization potential, it cannot fundamentally completely eliminate the polarization potential interference. (2) Mud interference is when the liquid-solid two-phase conductive fluid flow rate is measured. When solid particles or bubbles are rubbed across the electrode surface, the contact electrochemical potential of the electrode surface changes abruptly, and the electromagnetic flow sensor output signal has a spike-like interference noise. (3) Fluid flow noise is when the flow rate of low conductivity liquid (below 100μS/cm) is measured, the electrochemical potential of the electrode fluctuates periodically, and the random interference noise with increasing frequency increases with the increase of flow rate, with 1/f similar to mud interference. Spectrum characteristics. 3.2.2 Electromagnetic flowmeter anti-electrochemical interference technology The measures taken by the electromagnetic flowmeter to improve the anti-electrochemical interference capability are mainly low-frequency rectangular wave excitation and dual-frequency excitation technology. The low-frequency rectangular wave excitation has the characteristics of DC excitation technology not generating eddy current effect and transformer effect (orthogonal interference), and the power frequency sine wave excitation basically does not produce polarization effect, which is convenient for amplifying signal processing, and can avoid zero drift of DC amplifier. , noise, stability and other issues, have better anti-interference performance. Although low frequency rectangular wave excitation has excellent zero stability, it can not overcome mud interference and fluid noise interference when measuring the flow of liquid-solid two-phase conductive fluid containing fibers and solid particles such as mud and pulp. Research analysis shows that mud interference and flow noise have a spectral characteristic of 1 / f. The amplitude is large at low frequencies and small at high frequencies. If high frequency low frequency rectangular wave excitation is used, the magnitude of mud interference can be greatly reduced. Therefore, increasing the excitation frequency helps to reduce mud interference and flow noise, and improves the signal-to-noise ratio of the sensor output signal. In summary, to ensure the zero stability of the electromagnetic flowmeter, low-frequency rectangular wave excitation is used. In order to accurately measure the flow of liquid-solid two-phase conductive fluid and low-conductivity fluid, higher frequency must be used. Rectangular wave excitation. The method of using the dual-frequency rectangular wave excitation shown in Fig. 1 is a good solution. 3.2.3 Double-frequency rectangular wave excitation work and anti-interference principle An electromagnetic field containing two frequency components is formed in the measuring tube of the electromagnetic flowmeter: the high frequency excitation component is not affected by the liquid interference, and the low frequency excitation component has excellent zero point stability, and the component signals detected according to the high and low frequency timings After calculation, the flow signal can be obtained. The principle of dual-frequency rectangular wave excitation measurement is shown in Figure 1. An electromagnetic field superposed by high and low frequency components is applied to the liquid to be measured through the excitation coil, and the excitation waveform is a waveform obtained by superimposing a rectangular wave higher than the commercial frequency on a low frequency rectangular wave. In the generated electromotive force, the low frequency component obtains a smooth flow signal with good zero stability through a large time constant integration circuit. The low-frequency noise generated by the slurry or low-conductivity fluid can be suppressed by the high-frequency sampling circuit that is not affected by the noise. The flow signal with the same time constant passes through a differential circuit to determine the change of the flow rate signal. The combined signals are combined to obtain a stable flow rate signal that is immune to noise and has a high zero stability. 3.3 Power interference noise characteristics and electromagnetic flowmeter anti-jamming technology Basic signal relationship Electromagnetic flowmeters are generally powered by a commercial frequency AC power supply. The amplitude and frequency of the power supply voltage will cause power interference noise to the electromagnetic flowmeter. For the amplitude variation of the power supply voltage, due to the use of multi-level integrated voltage regulation, in general, the amplitude variation of the power supply voltage has little effect on the measurement accuracy of the electromagnetic flow. When the frequency of the power supply voltage fluctuates, although its fluctuation range is limited, it has a great influence on the measurement accuracy of the electromagnetic flowmeter. In order to solve the problem of power frequency interference and achieve accurate measurement of the fluid flow rate induced potential eab signal, the following basic relationship needs to be utilized: 1 the excitation period is an integral multiple of the power frequency period, that is, the excitation frequency is 50/nHz (n is an even number); In-phase sampling under positive and negative excitation. Fig. 2 is a typical potential signal form corresponding to the low-frequency rectangular wave excitation form. According to the above relationship, under an excitation period, if the points t1 and t2 are assumed to be the equivalent interference points of the power frequency interference, and the sampling width T=T1 = T2, Then the basic formula of eab [3] is: 00 (t2)=1 2T ∫t1 +T1 t1 e(t1 )dt-∫t2 +T2 t2 e(t2 )dt=eab (4) Equation (4) theoretically illustrates that the power frequency interference of the electromagnetic flowmeter can be overcome, that is, the synchronous sampling technique, which is based on the assumption of the same phase (t1=t2) and the same width sampling (T1 = T2 = T). The sampling frequency should be selected as an integral multiple of the power frequency period. Thus, even if the interference signal is mixed, since the sampling time is a complete power frequency cycle, the average value is zero, and the interference voltage does not work. 4 electromagnetic flowmeter selection 4.1 General principles for electromagnetic flowmeter selection [4] (1) Whether the medium to be tested is a conductive liquid or slurry, thereby determining whether an electromagnetic flow meter is selected; (2) The conductivity of the measured medium determines the type of electromagnetic flowmeter—whether it is high conductivity or low conductivity; (3) The nominal diameter of the large, small and common flow process pipelines required by the process, determine whether the flow rate of the medium is at a more economical flow point, whether the pipeline needs to be reduced, and then determine the diameter of the flowmeter; (4) Determine whether to use an integrated or split flowmeter, and the degree of protection of the flowmeter, etc., based on the layout of the process piping. (5) Selecting the electrode type according to whether the measured medium is easy to crystallize or crusting; (6) selecting an electrode material according to the corrosiveness of the measured medium; (7) The corrosiveness, wear and temperature of the measured medium determine the lining material to be used; (8) The high working pressure of the measured medium determines the nominal pressure of the flow meter; (9) The insulation of the process piping determines the type of grounding ring. 4.2 According to the characteristics of the electromagnetic flowmeter excitation mode (1) DC excitation type This type of electromagnetic flowmeter is small in number and is only used to measure the flow rate of liquid metal, such as mercury at normal temperature and liquid sodium and potassium at high temperatures. (2) AC power frequency excitation type The earlier electromagnetic flowmeter was excited by 50 Hz power frequency mains. Due to its vulnerability to electromagnetic interference and zero drift, it has been gradually replaced by low frequency rectangular excitation. However, when measuring the liquid-solid two-phase flow such as mud and slurry, the low-frequency rectangular wave excitation method can not overcome the spike noise generated by the solid rubbing on the surface of the electrode, but the power frequency AC excitation meter does not have this disadvantage, so there are still domestic and foreign Some electromagnetic flowmeters still use AC power frequency excitation. (3) Low frequency rectangular wave excitation type Since the low frequency rectangular wave excitation method has low power consumption and good zero point stability, it is the main excitation mode of the current electromagnetic flowmeter. The waveform has two values ​​of "positive-negative" binary value and "positive-zero-negative-zero". Some electromagnetic flowmeter excitation frequency can be set by the user. Generally, small-diameter instruments use higher frequencies, and large-diameter instruments use lower frequencies. (4) The waveform of the excitation current of the dual-frequency excitation type is to superimpose the high-frequency rectangular wave on the low-frequency rectangular wave, mainly to overcome the slurry noise and flow noise existing in the excitation of the binary rectangular wave, and improve the stability and response characteristics of the instrument, so Used in pulp and paper and sewage treatment industries. 5 Conclusion According to the above analysis, the electromagnetic flowmeter has many advantages such as high measurement accuracy, high speed, convenient use, wide measurement range, wide aperture, etc., but at the same time, the measurement output signal is susceptible to power frequency electromagnetic interference, fluid electrochemical noise and power supply. Disadvantages of frequency changes. Electromagnetic flowmeters with different excitation modes have different anti-jamming technologies and application ranges. Correct understanding of the characteristics of various excitation technologies and the technical principles of different electromagnetic flowmeters are prerequisites for the correct use of electromagnetic flowmeters. Floral Foam,Oasis For Flowers,Oasis For Artificial Flowers,Wet Floral Foam SHANGHAI WELLONG IMPORT AND EXPORT CO., LTD , https://www.shanghaifloralfoam.com