Electromagnetic Flowmeter Electromagnetic flowmeter use maintenance procedures Electromagnetic flowmeter (hereinafter abbreviated as EMF) is an instrument for measuring the volumetric flow rate of conductive liquids using Faraday's electromagnetic induction law. The basic principle of EMF is Faraday’s law of electromagnetic induction, that is, when a conductor cuts a magnetic force in a magnetic field, it generates an induced electromotive force at both ends. As shown in the figure, the conductive liquid flows in a non-magnetic measuring tube perpendicular to the magnetic field and generates an induced potential proportional to the flow in a direction perpendicular to the flow direction. The direction of the electromotive force is according to the "Fleming right hand rule", and its value is as follows formula: Where E - EMF, the flow signal, V; K - coefficient; B - magnetic induction, T; D——Inner diameter of measuring tube, m Let the liquid volume flow be q v (m 3 /s) and q v =âˆD 2 E=(4kB/âˆD)q v =Kq v Where K is the meter constant, K=4kB/âˆD. General things to note when using: ' The liquid should have the conductivity required for the measurement and require a substantially uniform distribution of conductivity. Therefore, the flow sensor should be installed so as to avoid places where conductivity is not easy to be generated. For example, liquid medicine is added near the upstream of the sensor. The liquid addition point is preferably located downstream of the sensor. When used, the sensor tube must be filled with liquid (except for non-full tube types). When mixed, their distribution should be generally uniform. The liquid should be at the same potential as ground and must be grounded. If the process piping is made of plastics and other insulating materials, the transport liquid generates frictional static electricity, which causes a potential difference between the liquid and the ground. Flow sensor installation: (1) Installation site Normal electromagnetic flow sensor housing protection class is IP65 (dust and spray water level specified in GB 4208), all the following requirements for the installation site. 1) When measuring the mixed phase fluid, select the location that will not cause phase separation; when measuring the two-component liquid, avoid installing in the downstream where the mixing is not uniform; when measuring the chemical reaction pipeline, install it in the downstream of the reaction fully completed section 2) Avoid as much as possible negative pressure in the measuring tube; 3) Select a place with little vibration, especially for integrated type instruments; 4) Avoid large electric motors, large transformers, etc. nearby to avoid electromagnetic interference: 5) It is easy to realize the place where the sensor is grounded separately; 6) Avoid high concentrations of corrosive gases as much as possible in the surrounding environment; 7) Ambient temperature at 25/l0-50/60. C within the range, the temperature of a body structure is subject to further electronic components, for a narrower range; 8) The relative humidity of the environment is in the range of 10% to 90%; 9) Avoid direct sunlight as much as possible; 10) Avoid rain soaking and will not be immersed in water. If the degree of protection is IP67 (dust-proof and anti-submerged) or IP68 (dust-proof submersible), the above 8) and 10) requirements are not required. (2) Straight pipe length requirement To obtain the normal measurement accuracy, the upstream electromagnetic flow sensor should have a certain length of straight pipe sections, but with most of its length as compared to other flow meters less demanding. After the 900 elbow, T-tube, concentric reducer and full-opening valve, it is generally considered that as long as the pipe section is 5 times the diameter (5D) from the center line of the electrode (not the connecting surface of the sensor inlet), valves with different opening degrees are Requires 10D; the downstream straight section is (2 - 3)D or no requirement; but prevent the butterfly valve piece from penetrating into the sensor measuring tube. The lengths of the upstream and downstream straight pipe sections proposed by various standards or verification regulations are also inconsistent. As summarized in Table 8.5, the requirements are higher than usual . This is due to ensure that the current O. Level 5 precision instrument requirements. IS0 6817 is a standard that uses EMF. This standard considers that any kind of flow disturbance should have at least straight IOD, and the performance change cannot guarantee more than 1%. IS0 9104 JJG l98 and the file is submitted for the assessment of the performance of EMF; straight pipe length JJG l98 listed in Table 0.5 for precision and to the instrument. Straight pipe length requirement Standard or certification procedure number Spoiler name IS0 6817 IS0 9104 JIS B7554 ZBNl2007 JJG l98 Elbow pipe, T -shaped pipe, full-opening valve, gradually expanding pipe 5D Upstream Reducing tube 10D or factory regulations lOD Visible as straight tube 5D lOD Various other valves 10D Downstream Various types Not requested 5D Not requested 2D 2D If the valve cannot be fully opened, the valve closure direction and the electrode shaft should be 45. Angle installation, the additional error can be greatly reduced. (3) Installation position and flow direction The sensor can be mounted horizontally, vertically or tilted without restriction. However, it is best to measure the solid-liquid two-phase fluid vertically and flow from bottom to top. This can avoid serious local wear in the lower half of the liner during horizontal installation and low flow rates Solid phase precipitation and other shortcomings. When installing horizontally, make the axis of the electrode parallel to the horizon, and do not be perpendicular to the horizon, because the electrode at the bottom is easily covered with sediments, and the top electrode is easily wiped by the bubbles in the liquid to cover the surface of the electrode, causing the output signal to fluctuate. . (4) Bypass tube, easy to clean connection and preset inlet In order to facilitate checking and adjusting the zero point when the process pipe continues to flow and the sensor stops flowing, the bypass pipe should be installed. However, large diameter pipe systems are often difficult to manage because of investment and location space constraints. It is difficult to correct the measured value according to the degree of contamination of the electrode or to determine a reference to the degree of contamination that does not affect the measured value. In addition to the foregoing, using a non-contact electrode or a meter with a gua- dao removal device electrode can solve some problems, and sometimes it is necessary to remove the internal wall attachments. The sensor can be cleaned in place without removing the sensor. For pipes with a pipe diameter greater than 1.5-1.6m, a manhole is preset on the pipe near the EMF so that the inner wall of the sensor pipe is cleaned when the pipe system is stopped. (5) Installation of negative pressure piping Fluoroplastic lining sensors should be used with caution in negative pressure piping systems; positive pressure piping systems should be designed to prevent negative pressures, such as pipe systems with liquid temperatures above room temperature, and the fluid cooling contraction will be negative after closing the upstream and downstream stop valves of the sensor. Pressure should be installed near the sensor negative pressure prevention valve. Some manufacturers require FIFE and PFA plastic linings to be used in negative pressure piping systems. The absolute pressures that can be used at 20°C, 100°C, and 130°C must be greater than 27, 40, and 50 kPa, respectively. (6) Grounding The sensor must be grounded separately (100Ω or less of ground resistance). In principle, the separation type should be grounded on the sensor side, and the converter grounding should be on the same grounding point. If the sensor is installed on the cathode corrosion protection pipeline, in addition to the sensor and the grounding ring together with the ground, but also with a thick copper wire (16mm 2 ) bypass the sensor across the two connecting flange flange, so that the cathodic protection current and sensor Isolation. Sometimes the stray current is too large. If the leakage current of the electrolyzer along the electrolyte affects the normal measurement of the EMF, the electrical isolation between the flow sensor and the connected process can be taken [8]. On the same cathodically protected line, the cathodic protection current can also be used when measuring the EMF's influence. (1) Zero check and adjustment Before the instrument is put into operation, the zero point must be adjusted when the sensor is filled with liquid static state. After operation, it is also necessary to periodically stop the flow to check the zero point according to the conditions of use of the liquid; in particular, for precipitation, easy-to-pollution electrodes, and non-clean liquids containing solid phases, more inspections should be conducted at the initial stage of operation to obtain experience and determine the normal inspection cycle. The AC excitation mode EMF is more likely to cause zero drift than the square wave excitation, so it is necessary to pay attention to inspection and adjustment. (2) Periodically check the electrical performance of the sensor 1) Roughly measure the signal connection between the electrode resistance disconnection sensor and the transducer. The sensor is filled with liquid. Use a multimeter to measure the resistance value of the two electrodes and the grounding terminal. Is it within the specified range of the manufacturer and the measured two values? It's about the same. Record the resistance value measured for the first time. This value is useful for determining the cause of the sensor failure later, such as whether the deposited layer is conductive or insulating. 2) Inspect the electrode insulation resistance sensor for venting the liquid, clean the inner wall, and measure the resistance between the two electrodes and the grounding terminal with a megohmmeter after it is completely dry. : 3) Check the insulation resistance of the excitation coil Remove the connection between the sensor excitation coil terminal and the converter and measure the insulation resistance of the coil with a megohmmeter. Source Keywords: electromagnetic flowmeter use maintenance procedures Protective Film,Soft Pvc Film,Car Isolation Film,Pvc Ceiling Film Nantong Kezheng Packing Co.,ltd , https://www.ntdazhengplastic.com
- Average flow rate, m/s. 
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