Installation guide for plug-in electromagnetic flowmeter

　　1、 Overview

　　Firstly, the plug-in electromagnetic flowmeter is an installation type of electromagnetic flowmeter. There are many installation methods of electromagnetic flowmeter, including flange installation, thread installation, clamp installation and plug-in installation. Flange installation is a common installation method, and threaded connection is mainly aimed at the installation of small diameter, Clamp type installation is characterized by convenient disassembly and easy cleaning. Plug in installation is mainly used in occasions with special installation conditions and large diameter. Because of its simple structure, light weight, convenient installation and small maintenance, this instrument is used to measure the volume flow of non corrosive (water supply and drainage) conductive liquid in closed pipelines in petrochemical plants.. This paper briefly introduces the structural characteristics and basic installation requirements of plug-in electromagnetic flowmeter, which can be understood by users who have just come into contact with electromagnetic flowmeter.

　　Plug in electromagnetic flowmeter

　　2、 Working principle, characteristics and application of plug-in electromagnetic flowmeter

　　(1) Measuring principle

　　Plug in electromagnetic flowmeter is an instrument for measuring conductive liquid based on Faraday's law of electromagnetic induction. The measuring tube of the flowmeter is provided with a shell made of insulating material, in which a coil, an iron core and a yoke are installed, and the end face of the shell is provided with two electrodes. When the excitation coil is excited by bidirectional square wave pulse, a working magnetic field with magnetic flux density B will be generated. When the fluid with certain conductivity flows through the measuring tube at the average flow rate V, the cutting magnetic line of force will induce the electromotive force E. Electromotive force E is proportional to flux density B

　　Product with average velocity V: e ∝ KVB, where k is the structure coefficient. Electromotive force E (flow signal) is detected by electrode and sent to converter through cable.

　　(2) Structural features

　　The plug-in electromagnetic flowmeter consists of two parts: sensor and converter; The transducer and sensor can be separated or simultaneous interpreting.

　　(3) The application range of plug-in electromagnetic flowmeter is the same as that of general electromagnetic flowmeter.

　　(4) Main technical characteristics and application of plug-in electromagnetic flowmeter

　　1. High accuracy. The measurement results are independent of the changes of physical parameters such as velocity distribution, fluid pressure, viscosity, temperature, density and conductivity.

　　2. It is suitable for use on metal pipes with nominal diameter of dn100-dn1800.

　　3. Wide range ratio. The range can be up to 100 ∶ 1.

　　4. It has corrosion resistance and wear resistance. Only the lining and electrode of the sensor are in contact with the measured liquid, as long as the electrode and lining materials are reasonably selected.

　　5. The converter adopts 16 bit high-performance microprocessor, 3 lines of 128 * 64 LCD dot matrix Chinese character display, convenient parameter setting and reliable programming.

　　6. Low requirements for straight pipes, first 5D and then 3D (D is the nominal diameter of the pipe).

　　3、 Installation of plug-in electromagnetic flowmeter

　　(1) Installation of separate converter

　　The separated converter shall be installed as close to the sensor as possible, which can be wall mounted or column mounted. Outdoor installation shall be installed in the instrument box to avoid direct sunlight and rain for a long time.

　　(2) Installation of sensor (or integrated). For the sensor (or integrated type) installed on the pipeline, the connecting seat (or pipe joint) shall be welded on the pipeline, and then the sensor (or integrated type) shall be fixed to the connecting seat (or pipe joint).

　　1. Technical requirements for installation on pipeline

　　(1) Choose a place with low vibration to avoid direct sunlight.

　　(2) In order to make the sensor measuring conduit always filled with fluid, the sensor can be installed at the low part of the U-shaped pipe.

　　(3) If installed vertically or obliquely, the fluid shall flow from bottom to top.

　　(4) The measured fluid needs to fill the pipeline.

　　(5) The sensor can be installed horizontally and vertically as long as it is perpendicular to the pipe axis through the geometric line of the two electrodes.

　　(6) In order to further reduce the influence of entrained bubbles on measurement, the instrument can be installed at a high position away from the pipeline.

　　(7) The location shall be selected to facilitate instrument wiring operation and reading.

　　2. The separated sensor (or integrated) is installed on the user's pipeline with flange ball valve.

　　(1) Drain the liquid in the pipe at the selected position.

　　(2) Open a pipe at the selected position of the pipe by gas cutting Φ 40- Ф 50 round hole, and the periphery of the hole shall be as smooth as possible.

　　(3) Remove the connecting seat from the lower end of the ball valve and place it at the opening.

　　(4) Install the sensor (or all-in-one) on the connecting seat, add a gasket between the connecting seat flange and the ball valve flange, and make the flow direction mark arrow point to the positive flow direction recognized by the user.

　　4、 Problems in the use of plug-in electromagnetic flowmeter

　　(1) Due to the improper installation position of the flow sensor, the liquid in the measuring pipe cannot be filled, resulting in "excitation" alarm.

　　(2) The straight pipe section in front of the flowmeter shall be ≥ 5D, and the straight pipe section behind the flowmeter shall be ≥ 3D (D is the nominal diameter of the pipeline).

　　(3) When the liquid contains powder and particles, it will cause the deposition of dirt and wear the lining.

　　(4) If the liquid conductivity is close to the lower limit, shaking may occur.

　　(5) The sensor excitation coil resistance (between ext + and ext -) shall be less than 60 Ω.

　　5、 Conclusion

　　The advantages of plug-in electromagnetic flowmeter are simple installation, wide use, good measurement performance and convenient transformation of old devices. It is widely used in the measurement of variable data of various water media (fresh water, circulating water, sewage, etc.), and can play an effective role in the water balance and measurement of the device. Therefore, mastering its working principle, structure, characteristics and solutions will be conducive to our better use and maintenance.