What is the principle of electromagnetic flowmeter?

What is the working principle of electromagnetic flowmeter

The electromagnetic flowmeter works based on Faraday's law of electromagnetic induction. The conductive medium in the measuring tube is equivalent to the conductor in Faraday's electromagnetic induction.

In the Rady test, two electromagnetic coils are placed through the upper and lower ends of a conductive metal rod to generate a constant magnetic field. When a conductive medium flows through it, an induced voltage is generated inside the pipe. To measure this induced voltage, two electrodes are installed inside the pipe. To achieve electromagnetic isolation from the fluid and measuring electrodes, the measuring pipes are lined with non-conductive lining materials such as rubber or Teflon. This design ensures measurement accuracy and protects the measuring electrode from corrosion and damage by the fluid.

The measurement accuracy of the sensor is not affected by changes in fluid properties. The induced voltage has a linear relationship with the average flow rate, so the measurement accuracy is high.

There are no flow obstructions in the measuring pipe, so there is no additional pressure loss; there are no moving parts in the measuring pipe, so the sensor has an extremely long life.

The induced voltage signal is formed in the entire magnetic field space and is the average value of the pipe surface. Therefore, the straight pipe section required by the sensor is shorter and the length is 5 times the pipe diameter.

The sensor part is only in contact with the liquid being measured, and through reasonable selection of electrodes and lining materials, corrosion resistance and wear resistance are achieved.

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The converter uses the latest microcontroller (MCU) and surface mount technology (SMT) to ensure reliable performance, high precision, low power consumption and stable zero point. The LCD display supports Chinese display and can display parameters such as cumulative flow, instantaneous flow, flow rate and flow percentage, making it easy to set parameters.

The bidirectional measurement system can measure forward and reverse flow, using special technology and high-quality materials to ensure long-term stability.

Classification of electromagnetic flowmeters: split electromagnetic flowmeter, integrated electromagnetic flowmeter

The split-type electromagnetic flowmeter is an inductive instrument that measures the volume flow of conductive media in a pipe based on Faraday's law of electromagnetic induction. It uses microcontroller embedded technology to realize digital excitation. At the same time, the electromagnetic flowmeter uses CAN field bus, which belongs to The first of its kind in China, the technology has reached the leading domestic level.

The split type electromagnetic flowmeter not only meets the needs of on-site display, but also can output 4~20mA current signals for recording, adjustment and control. It is now widely used in chemical industry, environmental protection, metallurgy, medicine, papermaking, water supply and drainage, etc. Industrial Technology and Management Sector.

In addition to measuring the flow rate of general conductive liquids, the split type electromagnetic flowmeter can also measure the volume flow rate of liquid-solid two-phase flow, high viscosity liquid flow, and salt, strong acid, and strong alkali liquids.

Brief description of the working principle of electromagnetic flowmeter

The measurement principle of the flow meter is based on Faraday's law of electromagnetic induction. Measurement of flow meter

The measuring tube is a short tube of non-magnetic alloy lined with insulating material. Two electrodes are placed along the diameter of the tube

Fixed to the measuring tube through the wall of the tube. When the coil is excited, it will be

with the axis of the measuring tube

A working magnetic field with a magnetic flux density B is generated in the vertical direction. At this time, such as

If a fluid with a certain conductivity flows through the measuring tube, it will cut the magnetic lines and induce electricity

Momentum E. The electromotive force E is proportional to the magnetic flux density B, and the inner diameter d of the measuring tube is proportional to the average

The product of the flow velocity v, the electromotive force E (flow signal) is detected by the electrode and passed through the electric current

The cable is sent to the converter. After the converter amplifies the flow signal, it can display the fluid flow

quantity, and can output pulse, analog current and other signals for flow control and regulation.

E=KBDV

In the formula: E-- is the signal voltage (v) between electrodes

B-- Magnetic flux density (T)

d--Measuring tube inner diameter (m)

V--Average flow velocity (m/s)

Current transformer principle and wiring scheme

In terms of basic structure and working principle, a transformer is a special transformer.

The number of primary winding turns of the current transformer is very small (some types of current transformers do not have one side winding, and the primary circuit passing through its core is used as the primary winding, which is equivalent to a number of turns of 1), and the primary winding is quite Thick; while the secondary winding has more turns and the conductor is thin. When working, the primary winding is connected in series in the circuit, and the secondary winding is connected in series with the current coil of the instrument, relay, etc., forming a closed loop. Since the impedance of these current coils is very small, the secondary circuit is close to a short circuit state when the current transformer is operating. (The rating of the secondary winding is generally 5A)

Regarding the selection, the selection is generally based on the conditions of the work site (temperature, humidity, etc.), rated voltage, primary current, secondary current (usually 5A), accuracy level conditions, and check its short-circuit dynamic stability and Thermal stability.

It must be noted that the accuracy level of current transformer is related to its secondary load capacity. The secondary load of the transformer shall not be greater than the rated secondary load limited by its accuracy level.

Connection plan:

A. One-phase connection is usually used in load-balanced three-phase circuits such as low-voltage power lines for measuring current or connecting to overload protection devices.

B. Two-phase V-shaped connection, in a three-phase three-wire system with an ungrounded neutral point, it is widely used to measure three-phase current, electric energy and for overcurrent relay protection.

C, two-phase current difference connection line, suitable for three-phase three-wire system with ungrounded neutral point, for current relay protection.

D. Three-phase star connection. The three current coils exactly reflect the current of each phase. It is widely used in three-phase four-wire systems with three-phase unbalance, such as TN systems. It is also used in three-phase unbalanced systems. in a three-phase three-wire system.

Precautions for use:

1. When the current transformer is working, the secondary side must not be open circuit

2. One end of the secondary side of the current transformer must be grounded

3. When connecting the current transformer, pay attention to the polarity of its terminals

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