Vacorda electromagnetic flowmeter is an inductive instrument that measures the volume flow of conductive medium in the pipe according to Faraday’s law of induction. It uses the embedded technology of single-chip microcomputer to realize digital excitation. At the same time, it uses CAN field bus on the electromagnetic flowmeter. While meeting the requirements of field display, the flowmeter can also output pulse signals or 4-20mA current signals for recording, regulation and control. It has been widely used in chemical industry, environmental protection Industrial technology and management departments such as metallurgy, medicine, papermaking, water supply and drainage.
Front of electromagnetic flow meter
1、 Working principle of electromagnetic flow meter
The electromagnetic flowmeter is based on Faraday’s law of induction. The main components of the sensor are: measuring tube, electrode, excitation coil, iron core and yoke shell. It is mainly used to measure the volume flow rate of conductive liquids and slurries in closed pipelines. Including highly corrosive liquids such as acids, alkalis, and salts. This product is widely used in industries such as petroleum, chemical, metallurgical, textile, food, pharmaceutical, papermaking, as well as environmental protection, municipal management, water conservancy construction, and other fields. The TXLDE series electromagnetic flow meter is a fully intelligent electromagnetic flow meter developed using the most advanced technology at home and abroad. Its all Chinese electromagnetic converter core uses a high-speed central processing unit. The calculation speed is very fast, the accuracy is high, and the measurement performance is reliable. The converter circuit design adopts international advanced technology, with input impedance up to 1015 ohms, common mode rejection ratio better than 100db, and external interference and 60Hz/50Hz interference suppression ability better than 90db, which can measure fluid medium flow with lower conductivity. The sensor adopts non-uniform magnetic field technology and a special magnetic circuit structure, making the magnetic field stable and reliable. It also greatly reduces the volume, reduces repetition, and makes the flow meter small and flowable.
2、 Characteristics of electromagnetic flow meter:
There are no movable components or flow blocking components in the pipeline, and there is almost no additional pressure loss during measurement.
The measurement results are independent of physical parameters such as flow velocity distribution, fluid pressure, temperature, density, viscosity, etc.
On site, the range can be modified online according to the actual needs of users.
High definition backlight LCD display, all Chinese menu operation, easy to use, easy to operate, easy to learn and understand.
Adopting a 16 bit embedded microprocessor, it has fast computing speed, high accuracy, programmable frequency low-frequency rectangular wave excitation, improving the stability of current measurement and low power consumption.
Fully digital processing, strong anti-interference ability, reliable measurement, high accuracy, and flow measurement range up to 150:1
Ultra low EMI switching power supply, with a wide range of power supply voltage changes and good EMC resistance
There are three internal integrators that can display the positive cumulative amount and the difference cumulative amount, and there is a non power-off clock inside that can record 16 power-off times
Equipped with digital communication signal outputs such as RS485, RS232, Hart, and Modbus.
Side of electromagnetic flow meter
1) Select the appropriate type based on the characteristics of the integrated and separated electromagnetic flow meters. The installation and wiring of the all-in-one electromagnetic flow meter is convenient, with moderate accuracy, and should not be installed below the ground to prevent the converter from being submerged by water. The separated electromagnetic flowmeter has high accuracy, and the converter and sensor are installed in different places, making it more suitable for situations with poor on-site environment (such as harmful, toxic, and easily flooded places). However, the installation and wiring are strict, otherwise interference signals may be introduced.
2) Choose the appropriate electrode form. For media that do not produce crystallization, scarring, or contaminate electrodes, standard electrodes can be used. Otherwise, scraper type cleaning electrodes or electrodes with cleaning connection devices can be used. For sludge measurement occasions, interchangeable electrodes can also be selected.
3) The electrode material shall be selected according to the corrosion Sexual selection of the measured medium.
4) Select lining materials based on the corrosiveness, wear resistance, and temperature of the tested medium.
5) Electromagnetic flow meter protection level. According to the national standard GB4208-1984, which is about the same as the International Electrotechnical Commission IEC standard (IEC529-7B), the standard of enclosure protection grade is: IP65 is water spray proof type, which allows the faucet to spray water on the instrument from any direction, and the water spray pressure is 30Kpa. The water output is 0.75m3/h, and the distance between the spray nozzle and the instrument is 3m; IP67 is an anti immersion type, meaning that the instrument can be fully immersed in water, and the high point should be at least 150cm underwater for a duration of at least 30min. IP68 is a submersible type that can work underwater for a long time. According to the above regulations, IP68 should be selected for instruments installed underground that are prone to flooding, and IP65 should be selected for instruments installed above ground.
6) The grounding shall be selected according to the insulation property of the connected instrument pipeline.
7) Select the nominal pressure of the electromagnetic flowmeter based on the high pressure of the measured medium. For flow measurements with medium pressures of 10MPa, 16MPa, 25MPa, and 32MPa, high-pressure electromagnetic flow meters should be selected.
Types of electromagnetic flow meters
3、 Precautions for installing electromagnetic flow meters:
The sensor of the electromagnetic flow meter should be installed vertically and the fluid should flow from bottom to top to ensure that the solid and liquid are in a mixed state. The reason is that solid substances (such as sediment and small stone particles) in the medium are prone to precipitation. In addition, if there are fish and weeds in the pipeline, the swimming of fish in the pipeline will cause the output of the flowmeter to swing back and forth; The swinging back and forth of weeds hanging near the electrode can also cause unstable output of the flowmeter. Install a metal filter screen at the upstream inlet of the flowmeter to block fish and weeds from entering the measuring tube.
Improper installation and operation of the electromagnetic flow meter to prevent negative pressure in the pipeline will cause negative pressure to be generated in the sensor. When both the upstream and downstream valves of the flow meter are closed simultaneously, if the temperature of the fluid is higher than the air temperature and contracts after cooling, there is a risk of negative pressure forming in the pipe pressure. Negative pressure causes the lining to peel off from the metal conduit, causing electrode leakage.
Add a negative pressure prevention valve near the split electromagnetic flowmeter, open the valve to connect to atmospheric pressure, to prevent negative pressure from generating inside the sensor. When a vertical pipeline is connected downstream of the split electromagnetic flowmeter,
If the upstream valve of the flow sensor is used to close or regulate the flow, negative pressure will form in the sensor measurement pipe. To prevent negative pressure, it is necessary to add back pressure or use downstream valves to regulate and close the flow rate.
Suitable maintenance space for split type electromagnetic flow meters. Large diameter flow meters are often installed in the instrument well, and for the convenience of pipeline installation, wiring, inspection, and maintenance, appropriate space needs to be left. For the convenience of observation, wiring, and maintenance, the instrument installation should be at a certain height from the ground for easy cleaning and installation.
4、 What issues should be noted when selecting the position on the pipeline for electromagnetic flow meters to measure correctly
1. Electromagnetic flow meter sensors can be installed on vertical pipelines, as well as horizontal or inclined pipelines, but the central connection of the two electrodes is required to be in a horizontal state.
2. The medium should ensure full pipe flow in the installation position to avoid insufficient pipe and gas adhesion to the electrode.
For solid-liquid two-phase fluids, * vertical installation is adopted to ensure uniform wear of the sensor lining and extend its service life.
4. When the medium at the installation position of the electromagnetic flowmeter is not enough for the pipe, the method of lifting the rear pipe of the Flux tube can be adopted to make it full. It is strictly prohibited to install the flowmeter at the pipe * point and the water outlet.
5. Modify the installation method of the pipeline:
When the medium flow rate cannot meet the requirements, a smaller diameter flowmeter should be selected. In this case, a tapered pipe with reduced diameter or a modified part of the pipeline should be used to make it the same diameter as the sensor, but the front and rear straight pipe sections must at least meet the requirements; Front straight pipe section ≥ 5DN, rear straight pipe section ≥ 2DN (DN is the pipe diameter)
6. The length of the straight pipe section before and after the electromagnetic flowmeter is: front ≥ 5DN, rear ≥ 2DN.
Maintenance and cleaning methods for electromagnetic flow meters:
In the application of electromagnetic flow meters in sewage and wastewater, it is normal. The main function of electromagnetic flow meters is to measure the closed liquid flow rate. However, after the measurement work is completed, the most important task is to clean the electrodes of the electromagnetic flow meter. Only by cleaning the electrodes thoroughly and properly cleaning and maintaining them can efficiency be improved in future work. This article discusses how to clean the electrodes of the electromagnetic flow meter:
1、 Mechanical removal method:
One option is to use a mechanical separator. A knife with a thin shaft is made of stainless steel, and the knife is led out through a hollow electrode. A mechanical seal is used between the thin shaft and the hollow electrode to prevent the medium from flowing out, thus forming a mechanical scraper. When rotating the thin shaft from the outside, the scraper rotates tightly against the electrode end plane to remove dirt. This scraper can be manually operated or automatically driven by a motor to remove the fine shaft.
2、 Ultrasonic cleaning method:
Apply the ultrasonic voltage of 45-65kHz generated by the ultrasonic generator to the electrode to concentrate the energy of the ultrasonic on the contact surface between the electrode and the medium, thereby utilizing the ability of the ultrasonic to break down dirt and achieve the purpose of cleaning.
3、 Electrochemical methods:
According to the principle of electrochemistry, there is an interface electric field between the electrode and the fluid, and the interface between the electrode and the fluid is caused by the presence of a double layer of electricity between the electrode and the fluid. Research on the electric field at the interface between electrodes and fluids has found that molecules, atoms, or ions of substances exhibit enrichment or depletion adsorption phenomena at the interface, and it has been found that most inorganic anions are surface active substances with typical ion adsorption patterns, while the surface activity of inorganic cations is very small. Therefore, electrochemical cleaning of electrodes only considers the adsorption of anions.
4、 Electrical breakdown method:
This method uses AC high-voltage electricity to be regularly added between the electrode and the medium, usually adding 30-100V. Due to the attachment of the electrode, its surface contact resistance increases, and the applied voltage is almost concentrated on the attachment. High voltage will break down the attachment and then be washed away by the fluid. For overall safety, the Electrical breakdown method must be used to clean the AC high-voltage power directly on the sensor signal output terminal when the flowmeter is interrupted for measurement, the signal line between the sensor and the converter is disconnected, and the power is cut off.
Post time: 10-07-23