An electromagnetic flow meter is a technological device that is widely used to measure the flow of a coolant, to measure the performance of liquid and gaseous substances. The undoubted advantages of such systems are: the implementation of the design using a minimum number of mechanical elements, the absence of hydrodynamic resistance, the highest accuracy of recording indicators.
Electromagnetic flowmeter - principle of operation
Devices of this category are equipped with conductors in which, due to the intersection of the magnetic field with the lines of force, an electromotive force is generated. The direction of current formed in the conductor is perpendicular to the direction of the magnetic field. This pattern is fully disclosed in the so-called Faraday's law, which explains the principle of electromagnetic induction.
When replacing a conductor with a flow of liquid that conducts electricity, a circuit diagram is obtained, according to which, in fact, it operateselectromagnetic flowmeter. Such devices can be equipped with permanent or electric magnets that are powered by alternating current.
In the measuring area of the flow meter is placed a pipe made of non-magnetic non-conductive material. Often this zone is equipped with insulating inserts made of inert plastic. The use of such elements helps to obtain the most accurate readings in the process of measuring the characteristics of the working environment.
Operating areas
In what areas is an electromagnetic flowmeter used? Such devices are most widely used in the field of accounting for energy and water resources. In particular, such devices are used in the arrangement of heating systems.
At present, the electromagnetic flowmeter is widely used in the biochemical, metallurgical, food industries. Construction organizations, ore-dressing enterprises, medical institutions resort to the use of devices of this category.
Electromagnetic flow meter is indispensable in the organization of automatic control systems for the flow of working media, where the main role is played by the degree of delay in the measurement of indicators. The device is used when tracking rapidly changing flow rates of liquid and gaseous substances.
Metrological errors
As shown by many years of practice in the operation of measuring instruments with a constant magnetic field, their average erroris about 1–2.5%. The indicated minus becomes noticeable when measuring the indicators of low-pulsating media. In this case, additional errors often occur, the cause of which is the polarization of the electrodes, which is reflected in the change in the resistance of the device converter.
Reducing the percentage of metrological errors in flow meters with a constant magnetic field is facilitated by the implementation of calomelium and carbon electrodes or conductors with platinum and tantalum coating in the design.
As for devices with an alternating magnetic field, there is no polarization of the electrodes, which can lead to errors in the readings. However, such devices have other effects that distort the signal:
- Transformer effect - when the liquid passes through the conductors, which form turns, the connecting wiring and electrodes form a transformer electromotive force. To compensate for this action, magnets with a constant switched current or compensating circuits are introduced into the measuring circuit of flowmeters with an alternating magnetic field.
- Capacitive effect - occurs due to a significant potential difference between the connecting wiring and the system responsible for the formation of a magnetic field. Errors in this case are compensated by careful shielding of system elements.
Checking electromagnetic flowmeters
How is the verification of electromagnetic flowmeters performed?The most accurate method here is static weighing (mass method). For its implementation, exemplary scales and a shut-off valve are used, which operates in the start-stop mode.
In the course of work, the net mass of the working fluid is determined according to the measurement of the weight of the container before and after filling when the medium passes through the flow meter for a certain time period.
The advantages of the verification method are:
- measurement accuracy of normalized flow indicators;
- possibility of correlation of results with values corresponding to state standards;
- possibility of verification of a flow meter that works with hot liquids;
- process automation.
Types of flowmeters
In addition to electromagnetic flow meters, there is a wide variety of other devices for measuring the characteristics of working media passing through pipelines. Currently, based on the principle of operation, the following groups of devices are distinguished:
- thermal;
- ultrasonic;
- vortex;
- Coriolis;
- mechanical;
- microflowmeters.
Next, we will briefly consider the features of each type of electromagnetic flow meters.
Heat meters
The principle of operation is based on a local change in the properties of the working fluid, for example, temperature in the flow, followed by measurement of indicators at a remote site from the place of impact. Specifiedthe method contributes to the calculation of the average speed of the movement of matter along the conductive paths.
Similarly, other characteristics of a substance, for example, the chemical composition, can be changed. However, in most cases, this approach is unacceptable, most often when it is necessary to operate flow meters in medical institutions.
Ultrasonic flowmeters
The operation of devices of this type is based on the ability of sound waves to propagate in a moving medium. By determining the source of the occurrence of ultrasound and its receiver, it is possible to judge the flow rate of the working medium according to the indicators of the movement of the wave in a certain segment.
Vortex meters
In the devices of this plan, the main functional element is a spherical or disk-shaped target. The part is fixed on a fixed elastic cable. When passing through the system, the flow of the working medium affects the target, which leads to its displacement. This, in turn, causes deformation of the cable, changes on which are recorded by special strain gauges. The information obtained contributes to the formation of judgments regarding the direction and speed of the flow of matter.
Coriolis meters
Structurally, such devices consist of a tube that is exposed to vibrations that come from an external generator. In the absence of liquid in the system, vibrations cause simultaneous acceleration of all sections of the tube. As the liquid passes through it, the so-called Coriolis force comes into action, whichdirected in opposite directions for the inlet and outlet flows of the substance. This leads to a shift in the vibration phase of the conductive tube and makes it possible to fix the necessary indicators.
Microflowmeters
This category of measuring devices includes flow meters, which are distinguished by their miniature design. The dimensions of a particular device are determined by the scope of its application. Such devices meet the needs of medical institutions and chemical production enterprises.
According to the principle of operation, each miniature device is a conventional flow meter - an electromagnetic meter. However, due to the possibility of operation in cramped conditions, the cost of such devices is an order of magnitude higher.
Mechanical flowmeters
This group includes devices that are structurally devoid of electronic elements. The flow rate here is measured by the effect of the medium on the mechanical turbines.
Despite the affordable cost of such flowmeters, their accuracy leaves much to be desired. Another disadvantage is the use of moving parts, which can become an obstacle to the movement of gaseous or liquid substances. However, despite the indicated minus, mechanical flow meters are widely used in domestic conditions when it is necessary to account for water consumption.
Electromagnetic Flow Meters - Common Models
Let's take a lookdemanded electromagnetic flowmeters, which are in the greatest demand in the domestic market.
The electromagnetic flowmeter "PREM" is designed to measure the volume and flow rate of electrically conductive liquid substances. Readings are displayed on external devices convenient for registration by the user. Such devices are suitable for operation in large industrial complexes, are used to service housing and communal services (as part of water and heat energy metering systems).
The Promag electromagnetic flow meter is suitable for recording high temperature media. It is a complex functional electronic device. Used mainly as part of modular structures in the implementation of high-tech processes in industrial areas.
"Peterflow" is an electromagnetic flow meter designed to record the volume and volume flow of liquids moving through the pipeline. Devices of this brand are in demand in the field of thermal power engineering, housing and communal services, and in industry. Distinctive features of such measuring devices are: the placement of electronic equipment in a separate, well-protected case, the presence of protection against unauthorized access, the implementation of convenient backlit graphic displays.
Electromagnetic flow meter "ERSV VZLET" is currently the most common metering device at housing and communal services. Applicable to register the volume flow of both cold and hot water.
The electromagnetic flow meter "RISE" is characterized by the absence of pressure losses in the measured sections of the pipeline, does not need to install additional filters. Information about indicators can be displayed on a frequency, pulse or logic output, depending on the needs of the user. The flow meter "RISE ER" electromagnetic has the function of controlling the emptying of the pipeline. The only comparative disadvantage of such systems is the need for installation on straight sections.
In closing
As you can see, the electromagnetic flow meter is an extremely accurate, functional measuring device. The primary converters of such devices do not contain elements protruding into the pipeline, textured parts and profile narrowing. These features provide minimal errors in the readings. Among other things, electromagnetic devices allow cleaning and maintenance of pipelines without dismantling the system elements.
