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Classification of electromagnetic flowmeters

Issuing time:2018-01-30 09:33

Classification of electromagnetic flowmeters

According to the different types of external magnetic field, there are mainly two types of electromagnetic flowmeter: direct current type and induction type. The direct-current electromagnetic current xerometer (figure 2) has an external constant-lower magnetic field B perpendicular to the tube axis, and two electrodes are installed at C and D to measure the electromotive force (emf) induced by the fluid when it traversed the magnetic field. Flow Q can be obtained by the following equation:


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Where A is the cross-sectional area of the pipeline; D is the pipe diameter; K is the correction coefficient, which is used to correct the influence of factors not taken into account in the derivation of the formula (such as the fact that the flow velocity in the flowmeter pipe is not uniform). In a constant flowmeter, k is about 0.8, but for an electromagnetic flowmeter of a specific size and for a specific working condition, the value of k is calibrated by the volumetric method (the volume that flows through it in a certain period of time). Magnetic fields can be generated by permanent magnets, usually made of an al-nickel-cobalt alloy. When the flow is large, because the pipe diameter is large, the non-core excitation winding is adopted to generate an approximately uniform magnetic field with its constant dc current.

The induction type electromagnetic flowmeter can be used when the measured body temperature is too high or the electrode is strongly corroded (figure 2). A and B are two ac excitation windings with the same number of turns (section is shown in the figure). The windings are in series, but the respective current directions are opposite. When the fluid is at rest, the resultant magnetic flux through the induction coil C is zero, so there is no induced alternating electromotive force in the coil. Alternating electromotive force (emf) is generated in the induction coil when the fluid is flowing. Based on this principle, there are many modifications. For example, a excitation winding is used, and one induction coil in the opposite direction is placed on each side of its symmetry and connected in series (figure 3). When the fluid flows, the magnetic field line moves towards the flow direction, making the surprised electromotive force in the induction coils on both sides not zero, thus indirectly indicating the size of the flow.

There are no other parts in the pipeline of the electromagnetic flowmeter, so it can be used to measure the flow of conductive fluid and non-conductive liquid of various viscosity (in which ionizing substances are added). Electromagnetic flowmeters are often used in the nuclear energy industry.

Electromagnetic flowmeter display mode is divided into: fractal type electromagnetic flowmeter, a type of electromagnetic flowmeter. Series nominal diameter DN15 to DN3000.

Fractal electromagnetic flowmeter is a kind of induction-type meter which CAN measure the volume flow of conductive medium in the tube according to Faraday's law of electromagnetic induction. It adopts the embedded technology of single chip microcomputer to realize digital excitation. At the same time, it adopts CAN field bus on the electromagnetic flowmeter.

The fractal electromagnetic flowmeter can output 4 ~ 20mA current signal for recording, regulating and controlling while meeting the needs of field display. It has been widely used in chemical industry, environmental protection, metallurgy, medicine, papermaking, water supply and drainage and other industrial technology and management departments.

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

A one-body electromagnetic flowmeter is developed according to Faraday's law of electromagnetic induction and is used to measure the volume flow of a conducting fluid. Due to its unique characteristics, it has been widely used in industrial measurement of various conductive liquids. It is mainly used in chemical industry, papermaking, food, textile, metallurgy, environmental protection, water supply and drainage, etc.

1. The electromagnetic flowmeter has no moving parts or flow arrestors, which will not cause pressure loss, wear and obstruction.

2. Electromagnetic flowmeter is a volume flow measurement instrument, the measurement process is not subject to the temperature, viscosity, density and conductivity of the measured medium (within a certain range).

3. The range of the electromagnetic flowmeter is wide, up to 1:100. In addition, the electromagnetic flowmeter is only proportional to the average velocity of the medium under test, and is independent of axisymmetric flow states (laminar or turbulent).

4. Electromagnetic flowmeter without mechanical inertia, responsive, can measure the instantaneous pulse flow, and good linear, so the measurement signal can be directly used to convert the linear converter into standard signal output. Ld-t can be local indication, LD can be long distance transmission.


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