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Product introduction and technical indicators of electromagnetic flowmeter

1.1 Electromagnetic flowmeter product type and scope of application

Electromagnetic flowmeters are composed of electromagnetic flow sensors and electromagnetic flow converters, which are mainly divided into two categories: integrated and separated.

Electromagnetic flowmeter is a flow meter based on the principle of Faraday's law of electromagnetic induction. It is used to measure the volume flow of conductive liquid and slurry in a closed pipeline. It is widely used in flow measurement and control in the production process of petrochemical industry, iron and steel metallurgy, water supply and drainage, water conservancy irrigation, water treatment, environmental protection sewage, papermaking, medicine, food and other industrial and agricultural sectors.

1.2 Product features

1. Strong independence, the measurement is not affected by changes in physical quantities such as liquid density, viscosity, temperature, pressure, and conductivity.

2. Simple structure, low failure rate, no moving and blocking parts in the measuring tube, no blockage, no pressure loss.

3. Wide application range, wide range ratio, suitable for conductive liquids, liquids containing fibers, solid particles and suspended solids.

4. Low installation requirements and low requirements for straight pipe sections (first 5D and rear 2D).

5. Stable and reliable operation, using low frequency square wave excitation, low power consumption, stable zero point.

6. Diversified output signals, which can output linear analog signals, digital signals and alarm signals that are proportional to the flow rate.

1.3 Working principle (see Figure 1-1)

The measurement principle of flowmeter is based on the law of Faraday electromagnetic induction. The measuring tube of the flowmeter is a short non-magnetic alloy tube lined with insulating material. Two electrodes are fixed on the measuring tube through the tube wall along the tube diameter direction. The electrode tip is basically flush with the inner surface of the lining. When the excitation coil is excited by a two-way square wave pulse, a working magnetic field with a magnetic flux density of B will be generated in the direction perpendicular to the axis of the measuring tube. At this time, if a fluid with a certain conductivity flows through the measuring tube, the electromotive force E will be induced by cutting the magnetic field lines. The electromotive force E is proportional to the magnetic flux density B. The product of the inner diameter d of the measuring tube and the average flow velocity V, the electromotive force E (flow signal) is detected by the electrode and sent to the converter through the cable. After the converter amplifies the flow signal, it can display the fluid flow, and can output pulses and analog current signals for flow measurement and control.

Where:

E--------- is the signal voltage between the electrodes (v)

B---------Magnetic flux density (T)

d--------Inner diameter of measuring pipe (m)

V--------average velocity (m/s)

K--------Constant

Since K is a constant and the excitation current is constant, so B is also a constant. From equation (1-1), we can see that the volume flow Q is proportional to the signal voltage E, that is, the signal voltage E induced by the flow rate is linear with the volume flow Q relationship. Therefore, as long as E is measured, the flow rate Q can be determined. This is the basic working principle of an electromagnetic flowmeter.

It can be seen from the formula (1-1) that the temperature, density, pressure, conductivity of the measured fluid medium, and the liquid-solid composition ratio of the liquid-solid two-phase fluid medium will not affect the measurement results. As for the flow state, as long as it conforms to the axisymmetric flow (such as laminar flow or turbulent flow), the measurement result will not be affected. Therefore, the electromagnetic flowmeter is a real volume flowmeter.

Overview of Liquid Turbine Flowmeter

Turbine flowmeter is a kind of velocity flow meter, also called impeller flowmeter, based on the principle of conservation of moment of momentum.

The structure of the turbine flowmeter is shown in Figure 1-1 and Figure 1-2 on the right. When the fluid flows in the pipeline, it impacts the turbine blades, causing the turbine to rotate. The rotation speed of the turbine changes with the flow rate. Finally, it is calculated from the number of revolutions of the turbine. The flow value is counted and displayed on the secondary instrument, which can reflect the instantaneous flow and cumulative flow (or total), and can also be converted into a standard signal for remote transmission. In addition, the pulse frequency signal output by the sensor can be used alone with a computer, and the computer replaces the flow display instrument to achieve density, temperature, and pressure compensation, and display fluid volume flow or mass flow. It is one of the more mature high-accuracy meters in the current flow meters.