Magmeter is a volumetric flow meter that measures the flow of conductive fluid in a closed pipeline. Magmeter is also called electromagnetic flow meter, magnetic flow sensor, magnetic flow meter, etc. Magmeters is based on electromagnetic induction technology and outputs 4-20mA and other signals. Used in wastewater treatment, sewage treatment, chemical plants, etc.
First, let us look at the structure of the magmeter.
The structure of electromagnetic flowmeter is mainly composed of magnetic circuit system, measuring catheter, electrode, shell, lining and converter.
Magnetic flow meter principle
The electromagnetic flowmeter is made according to Faraday’s law of electromagnetic induction. It is used to measure the volume flow of conductive liquid.
Faraday’s law of induction (referring to the induction of an electric potential inside the conductor when the conductor passes through a magnetic field) is the basic principle of electromagnetic flowmeter measurement.
This measurement principle can be applied to conductive fluids.
The fluid flows into a pipe whose magnetic field is perpendicular to the direction of the fluid, and the electric potential induced in the fluid can be measured using two symmetrically arranged electrodes.
The signal voltage UE is proportional to the magnetic induction intensity B, the electrode spacing D and the average fluid velocity v.
Because the magnetic induction intensity B and the electrode spacing D are constant. Therefore, the signal voltage UE is proportional to the average flow velocity v.
The equation used to calculate the volume flow rate shows that the signal voltage UE is linearly proportional to the volume flow rate.
The sensed signal voltage is converted into the graduation in the converter, analog and digital output signals.
Magmeter flowmeters measure the velocity of conductive liquids (such as water, acid, caustic and slurry) in the pipeline. When measuring deionized water, the minimum conductivity of the medium is 20uS/cm. For most liquids, the minimum conductivity required for measurement can be 5uS/cm.
Magmeter is mainly used in the following areas:
Measure clean water, sewage, domestic water, raw water;
Various acid, alkali, salt and other solutions;
Mud, mineral pulp, paper pulp, and food liquids, etc.;
It is widely used in metallurgy, papermaking, water treatment, chemical industry, light industry, textile, food and beverage, catering, agricultural irrigation, hydropower station, oil production, electric power and mining industries.
Magmeter liner selection should be selected according to the corrosiveness, abrasiveness and temperature of the measured medium.
Hard/soft rubber is resistant to general weak acid and alkali corrosion. Temperature resistance is 65℃. Soft rubber has abrasion resistance.
Polytetrafluoroethylene (PTFE) is almost resistant to strong acid and alkali corrosion except hot phosphoric acid. The temperature of the medium can reach 130℃. But it is not resistant to wear.
Polyurethane rubber has good wear resistance. But it is not resistant to acid and alkali corrosion. Temperature resistance is also poor. The medium temperature is less than 65°C.
1. It is resistant to hydrochloric acid, acetic acid, oxalic acid, ammonia, phosphoric acid and 50% sulfuric acid, sodium hydroxide, and potassium hydroxide at room temperature. 2. Avoid strong oxidants.
1, below 70℃ 2. General acid, alkali, and salt solutions.
1. It has good elasticity and good wear resistance; 2. It is resistant to the corrosion of general low-concentration acids, alkalis, and salt media, and is not resistant to the corrosion of oxidizing media.
1. The material with the most stable chemical properties in plastics. It can withstand boiling hydrochloric acid, sulfuric acid, nitric acid and aqua regia, as well as strong alkalis and various organic solvents; 2. Poor abrasion resistance and adhesion.
1.-40℃~+130℃C(PTFE), -40℃~+160℃(PFA); 2. Strong corrosive media such as acid and alkali; 3. Sanitary media.
1. It can withstand hydrochloric acid, acetic acid, oxalic acid, ammonia, phosphoric acid, sulfuric acid, sodium hydroxide, and potassium hydroxide at room temperature. 2. It can withstand concentrated alkali and various organic solvents.
1. Below 70℃; 2. General acid, alkali, and salt solutions; 3. General water, sewage, mud, mineral slurry.
Wear resistance, high temperature resistance, corrosion resistance
Magmeter flowmeter, especially the flowmeter with intelligent LCD screen. The installation position should avoid direct sunlight as much as possible. The ambient temperature should be between 5℃~55℃.
2.Avoid strong interference sources
Choose a place where there is no strong electromagnetic field radiation to install the flowmeter.
Avoid devices that can easily cause electromagnetic interference, such as motors, transformers, and frequency converters.
The measurement principle of the flowmeter is based on Faraday’s law of electromagnetic induction, the original The initial signal is very weak, less than millivolt.
If there is strong electromagnetic field radiation near the flowmeter, it will affect the accuracy of the measurement and even fail to work normally.
3.Magmeter straight run
Pay attention to avoid eddy current generating parts as much as possible. Such as various valves, elbows, bypasses, etc.
Try to extend the straight pipe section upstream and downstream of the flowmeter. Install a rectifier tube if necessary.
Ensure that the upstream straight pipe section of the flowmeter must be at least 5 DN (measurement pipe diameter). The downstream is guaranteed to be more than 2 DN.
4.The conductivity of the liquid must be uniform and stable
Do not install the flowmeter in a place where the conductivity of the fluid to be measured is extremely uneven. If different media are injected upstream, the conductivity will be uneven and will affect the measurement.
In this case, it is recommended to move the injection port downstream.
If it must be injected from upstream, it should be as far away from the flowmeter as possible. Generally, it is better to keep a distance of more than 20 DN. To ensure that the liquid is fully mixed and uniform.
5.Keep the electrode axis level
The plane of the intermittent measuring electrode must be kept level. This prevents short-term insulation between the two electrodes due to air bubbles.
6.Magmeter grounding rings
Since the induction signal of the electromagnetic flowmeter is very weak, it is susceptible to noise. Therefore, the reference potential of the sensor and the converter must be the same as the measured liquid, and be grounded together.
The purpose of installing grounding rings or grounding electrodes on both sides of the electromagnetic flowmeter is to establish the equipotentiality between the flowmeter casing and the liquid.
Ordinary metal pipe (generally no need to install grounding ring)
When the pipeline itself is well grounded, the grounding wire can be omitted, but the casing must be connected to the liquid through the grounding wire equipped with the flowmeter.
A grounding ring (or grounding electrode) should be installed at both ends of the sensor and the measured medium should be short-circuited with the earth through the grounding wire.
Cathodic protection pipeline
The pipe flanges are connected by copper wires, but they must be insulated from the grounding wire.
Magnetic flowmeter is a widely used flow measuring instrument. How should we calibrate it?
Let’s take a look at the calibration method of electromagnetic flowmeter:
Determine the corresponding water pump according to the pipe diameter and flow rate of the verification test;
After the flowmeter is correctly installed and connected, it should be energized and preheated for about 30 minutes in accordance with the requirements of the verification regulations;
If the high-level tank water source is used, check whether the overflow signal of the stabilized water tower appears. Before the formal test, use the verification medium to circulate in the pipeline system for a certain period of time. At the same time, check whether there is any leakage in the sealing parts of the pipeline;
The verification medium should be filled with the electromagnetic flowmeter sensor before the formal verification. Then the downstream valve should be closed to adjust the zero position;
At the beginning of the verification, open the valve at the front of the pipeline and slowly open the valve behind the electromagnetic flowmeter to adjust the flow at the verification point.
During the calibration process, the flow stability of each flow point should be within 1% to 2%-flow method. The total amount law can be within 5%.
The temperature change of the verification medium should not exceed 1℃ when the verification process of a flow point is completed. It should not exceed 5℃ when the entire verification process is completed.
There must be a sufficiently high pressure downstream of the electromagnetic flowmeter to be checked to ensure that no flashing and cavitation occur in the flow pipeline;
After the test, close the valve at the front end of the test pipeline. Then stop the pump to avoid emptying the voltage stabilization facility. At the same time, the remaining verification medium in the test pipeline must be vented and the control system and the air compressor must be closed.
All electromagnetic flowmeters need to be calibrated when they leave the factory. Each finished product needs to pass the calibration line inspection before leaving the factory.
It is to install the product on the assembly line. The front end adopts a strictly debugged standard table. A series of coefficients such as the diameter of the flowmeter, the damping coefficient, and the sensor coefficient of the electromagnetic flowmeter are set at the back end. To achieve the same flow rate as the standard meter.
If calibration is done on-site, it may generally be used to calibrate outside the sealed pipeline. Such as portable ultrasonic flowmeter. But the accuracy is generally 0.5. If you just check it, you can use a portable ultrasonic flowmeter.
Ultrasonic flow meters and electromagnetic flow meters have different measurement principles.
Electromagnetic flowmeter must measure conductive liquid. The ultrasonic flowmeter can measure pure single-phase liquid. It has nothing to do with the conductivity of the liquid.
The electromagnetic flowmeter must be in contact with the medium to measure. The ultrasonic flowmeter can do contact and non-contact measurement.
The electromagnetic flowmeter is a flow measuring instrument. The measuring principle of the electromagnetic flowmeter is measured according to its principle of conduction. Most of the flow measurement on the market is solved by electromagnetic flowmeters.
The electromagnetic flowmeter is a pure liquid volume measurement instrument.
The mass flow meter is a function of fluid volume and fluid temperature and pressure. Is a dependent variable. The quality of a fluid is a quantity that does not change with time, space temperature, and pressure.
Mass flow meters are compared with electromagnetic flow meters. It can measure non-conductive media. This is one of the biggest differences. In addition, the accuracy of the mass flow meter is higher. The cost is large, and there are fewer applications in the market.
There is a big difference in the performance of general-purpose electromagnetic flowmeters on the market. Some have high precision and many functions. Some have low precision and simple functions.
The basic error of the instrument with high accuracy is (±0.5%～±1%)R. The instrument with low accuracy is (±1.5%～±2.5%)FS. The price difference between the two is 1 to 2 times.
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Magnetic flow meter manufacturers
Sino-Inst is one of the reliable Magnetic flow meter manufacturers and suppliers in China. Magnetic flow meters apply for wastewater flow rate measurement.
Sino-Inst can offer stainless steel magnetic flow meters, both the Pipeline and plug-in style. Of course, Sino-Inst can offer you with the mass flow meters and other flow meters.
Sino-Inst will offer you Magnetic flow meters with the Best Price. Reference price, $300-400/piece, DN10-DN2000. For special measuring media, we offer special lining materials: F4, F46, Fs, neoprene, urethane rubber, etc.
Sino-Inst offer over 20 Magnetic flow meters, with Best Price. A wide variety of Magmeters options are available to you, such as free samples, paid samples.