This article contains everything you need to know about magnetic flow meters.
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A magnetic flow meter is a mass or volumetric flow meter that uses electrodes connected to the liquid flow to measure the velocity of liquids in a tube or pipe. The unique design of magnetic flow meters allows them to take their readings without the need for any moving parts. This particular feature gives them the ability to measure high pressure applications without any fear of seepage or leakage.
Fluids measured by magnetic flow meters have a conductivity of three micro siemens or greater. They use Faraday’s law to measure voltage and velocity of fluids, which requires that fluids maintain a certain level of conductivity to generate the necessary voltage. The required conductivity varies between manufactures but is always between 3 to 10 micro Siemens with some manufacturers having higher requirements.
The consistency and accuracy of magnetic flow meters is unaffected by temperature, pressure, viscosity of liquids, or liquid density. Greasy viscose materials are easily and efficiently measured using this unique device.
To engineers, magnetic flow meters are known as electromagnetic meters and magmeters. The three names are used interchangeably with magmeters being the most common.
The basis of a magnetic flow meter is the magnetic field that it generates, which is used to measure and calculate the flow of a conductive liquid. As the speed of the flow increases, the voltage that it generates becomes greater and passes a signal to the meter. In essence, a magnetic flow meter measures the speed or velocity of a conductive liquid or fluid as it flows and moves through a pipe or conduit.
The concept of a magnetic flow meter is based on Faraday‘s Formula where the signal voltage (E) is proportionally constant (k) to the liquid Velocity times the magnetic field strength (B) times the distance between the electrodes (D). For this principle to work, the fluid being monitored and measured must be electrically conductive.
Michael Faraday proved that electric current is generated by a magnetic field when a conductor is moving at a 90o angle to the field. When a conductor is placed in the generated magnetic field, it induces an electromagnetic field (EMF).
Two field coils are positioned inside the magnetic flow meter using rods and generate a magnetic field across the tube to be measured. Electrodes, installed in the sides of the tube or pipe at right angles, pick up the electrical voltage. As a protection and to avoid an electrical short circuit, a lining is placed inside the wall sensor between the conductive fluid and the metal body.
When the tube or pipe is empty, there isn‘t induced voltage between the electrodes, and electrically charged particles are distributed evenly. When flow begins, the magnetic coils apply force to charged particles separating the positive and negative particles, collecting the negatively charged particles on one side of the pipe. The positively charged particles produce electrical voltage that is detected by the electrodes. The strength of the induced voltage is proportional to the flow rate of the conductor.
The meter for the magnetic flow meter calculates the movement rate of the fluid in the pipe using the voltage, the strength of the emitted magnetic field, and the distance between the electrodes. From the readings and data, the meter supplies information regarding the rate and totalized flow of a variety of liquids such as water, polymers, surfactants, and chemicals.
The induced voltage is carried to the transmitter through the electrode circuit. The transmitter takes the data from the electrodes and converts it into a quantifiable flow velocity. With the known velocity and the area of the pipe, the volumetric flow rate of the fluid can be calculated and displayed on the meter as seen below.
A major benefit of magnetic flow meters is their lack of complexity. They consist of two basic components one of which is connected to the pipe and the other collects the readings. These two pieces are the sensor and transmitter where the sensor is connected to the pipe and the transmitter sets on top of the sensor, as can be seen in the diagram below.
Each industry that deals in flow rates requires metering devices that specifically meet the needs of their operation. This same aphorism applies to the purchase of an electromagnetic flow meter. Each type of electromagnetic flow meter varies according to the needs of the application and its cost with inexpensive varieties being very simple while more accurate and complicated versions are more costly.
The three common types of electromagnetic flow meters are insertion, in-line, and low flow. The determination of which one to choose depends on the needs of the application and the required data.
Insertion magnetic flow meters can be installed through a ball valve or by drilling a hole in the pipe where hot tap or insertion installation is desired. They can be installed in pipelines with an internal diameter of two to 360 inches through a small tapping. As with other magnetic flow meters, insertion magnetic flow meters have an electromagnetic sensor and flow converter. A major benefit of insertion flow meters is that they can be installed where there is limited space.
To activate the flow meter it is attached to the pipe by being screwed into the joint. When it is being inserted, it is important that the indicators are parallel to the pipe and the flow of the fluid. The probe must be inserted such that the sensor is in the center of the pipe and conforms with the meter‘s installation depth chart.
In-line flow meters are attached to the pipe by cutting out a section and inserting the flow meter. This requires that the diameter of the flow meter sensor be the same as the pipe or be attached using an adapter. Flanges are placed on the pipe with gaskets to screw on the flow meter. In-line magnetic flow meters come in a wide variety of sizes from ones that are handheld to ones that require a lift mechanism to install them.
It is important that the meter be installed with the flow direction matching the arrow on the side of the meter if there is one. Due to their sensitivity to sound, in-line flow electromagnetic flow meters must be installed away from motors, transformers, and electromagnetic fields.
One of the difficulties, when measuring liquid flow, is fluids that move very slowly and are difficult to meter, such as chemical injections. For those conditions, low flow magnetic flow meters are used for applications with pulsating metering pumps. These uniquely designed meters are capable of measuring the flow of substances with particulate matter without clogging or jamming the flow pipe. Their design allows them to monitor fluids with widely varying viscosities and densities.
When deciding on a magnetic flow meter, there are certain considerations that need to be examined. Flow velocity is one of the criteria engineers use when making their selection. Though there are wide variations in the types of fluids, there are some standard norms. The properties of fluid flow are defined as the ratio of its inertial force to its drag force. With magnetic flow meters, the rate of flow is measured in feet per second.
The most common installation of magnetic flow meters is horizontal with the meter always being filled with liquid with the electrodes kept in the axial direction. Pipe fitting reducers can be used to fit small diameter magnetic flow meters to the flow pipe. Such an adjustment does not have any effect on the meter’s readings.
The meter should be properly grounded and have electrical contact with the liquid being processed. Viscosity, temperature, and sludge or grease bearing liquids do not have any influence on the meter’s readings.
When the magnetic flow meter is working, the pipeline should be full of fluid.
Magnetic flow meters are installed between elbows, valves, and pumps with straight pipe before and after the sensors.
When more than one magnetic flow meter is installed, they should be positioned two sensors apart. If two sensors are installed in parallel, they should be greater than one meter apart.
The signal generated by magnetic flow meters is very small and requires that they be grounded.
For partially full pipes, the magmeter electrodes are located at the bottom of the pipe, at 0.1 the pipe diameter, in order to be covered by the fluid. The flow meter measures the flow rate using capacitance level sensors embedded in the liner of the pipe. It is necessary for the flow meter to have compensation provided for wave action, calibration for full pipe, no flow or static level, and partially filled pipe operation.
Electromagnetic flow meters for partially full pipes have a magnetic field distribution that makes it possible for them to precision measure flow at both full and low levels. They are the ideal solution for measuring municipal and industrial wastewater in pressureless transport lines. Electromagnetic flow meters for partially full pipes are bidirectional close measurement systems designed for gravity pipelines and sewers.
The main use for magnetic flow meters is for measuring the flow rate of conductive fluids and dirty liquids. Though these are two primary functions, they are also used for measuring volumetric flow for other fluids due to the fact that they are easy to maintain and do not have moving parts.
The one rule that restricts the use of magmeters is that the fluid must be conductive. This one factor may limit its use for a certain number of fluids. Of the various types of flow meters on the market, electromagnetic meters are the third most used and are the most precise.
Substances that have suspended solids, such as cement, coal, and fly ash mixed with a liquid to create a mud-like material, is referred to as slurry. Measuring of these types of fluids is extremely challenging and difficult due to their abrasive nature and the harm they do to flow meters. In addition, fluids that are caustic or acidic enhance these difficulties. To fit the needs of these conditions, specially designed magnetic flow meters are used since their readings are not influenced or harmed by the characteristics of the flow material.
Various applications require the recovery of heated fluids and liquids that need to be disposed of or sent to be recycled, cleaned, or stored. To ensure the accuracy of each of the different processes, requires that the volume of the fluid be accurately measured. Of the available methods for flow measurement, magnetic flow meters have been found to be the only type of meter that can endure the heat and withstand the particulate content of heated fluids as well as provide accurate data.
The demands of modern water usage require that metering devices be durable, accurate, and reliable using the most advanced technologies. These characteristics are a necessity for the capturing of revenue costs and control of operational expenses. Regardless of the application, electromagnetic meters are a total solution for providing accurate data in regard to water utility metering and monitoring.
Since magnetic flow meters are adaptable to any conditions, they can be used for a wide range of water flow rates in varied and unusual conditions. Using embedded sophisticated technologies, magnetic flow meters supply the most up to date and accurate data for water usage monitoring.
There are a limitless number of industries that make use of magmeters due to their adaptability and versatility. Additionally, magnetic flow meters are inexpensive to install, operate, and maintain making them an excellent means for supplying accurate and reliable data regarding fluid movement.
As electromagnetic flow meters have become more accurate and precise, industries that deal with fluid flow have come to rely on them as an efficient means for calculating and determining liquid usage. The increase in need has heightened the use of magnetic flow meters.
Much like the petroleum industry, the chemical industry relies on magmeters to provide accurate and precise measurements of product flow. Included in their use is a safety factor since any misinformation or miscalculation can have disastrous and catastrophic consequences. Magnetic flow meters play a vital part in ensuring the chemical measurements are accurate and precise to assist in product quality and safeguarding of the system.
One of the magnetic flow meters that has the most use in the chemical industry is the low flow rate type of meter that can handle flow rates as low as 0.33 liters per minute.
It is easy to understand why magnetic flow meters are necessary for gas station use since it involves the sales and supplying of the product. Though there is a major need for mass flow meters at gas stations, magnetic flow meters are used for volumetric measurement of the flow of fuel. They are used for accurate billing of customers and measuring of fuel being supplied to the station.
A difficulty that distilleries face is the many types of liquids that flow through their production system. Since magnetic flow meters are not influenced by changes in the types of fluid in the system, they are ideal for distillery use. The multiple uses for magnetic flow meters for the distillery industry include measuring, recording, monitoring, and regulating fluid flow. These various functions are necessary to ensure the quality and standards for the products being produced. A secondary function is controlling fluid flow during packaging. A major benefit to the distillery industry regarding the use of magmeters is their lack of susceptibility to temperature, pressure, and fluid changes, which removes the need to change or adjust the meter during operation change over.
A critical requirement of the water supply industry is that the supply readings be accurate for billing purposes. Every business, home, office, and industry use water for a variety of reasons and demand that they be billed in accordance with their usage. It is for this reason that magnetic flow meters are an essential part of providing accurate readings that precisely measure water usage. The billing process is directly affected by the data collected by magnetic flow meters as well as detecting leakages and pipeline abnormalities.
One of the by-products of mining operations is the production of thick heavy sludge that is pumped out as minerals are removed. This abrasive and dense material has to be precisely controlled and monitored for the safety of the operation. The ability of magnetic flow meters to measure flow regardless of its density or viscosity has made them an ideal monitoring device for mining operations. The data captured by the meter is collected and sent to be translated into mass flow measurements such that slurry movement and flow can be closely controlled.
Dairies use flow meters to measure the amount of waste coming from the dairy, which has to be regulated and controlled. An additional aspect of the flow is to determine the amount of waste that is available for the production of fertilizers for conservation and repurposing. Since magnetic flow meters are adaptive and adjustable, they can be installed in various locations on the waste pipeline. The essential part of their function is to provide accurate and reliable data for the determination of the use of the waste material.
In the management of wastewater, it is necessary to measure the flow for full treatment (FFT) to determine the maximum amount of wastewater that the plant can treat. The design of wastewater facilities is built on an estimation of the flow, the volume of water that can go through the plant. The rules for the construction of a wastewater facility are based on the rules from the Environmental Protection Agency (EPA) that state "to treat peak dry weather flow (DWT) and additional flows from light rainfall."
This means that a plant must determine its minimum capacity of flow, which occurs during dry periods. From this determination, they calculate the capacity of the treatment operation as three times that of a dry period. The monitoring and control of the flow is dependent on the readings taken by a magnetic flow meter, an essential and critical instrument that is necessary for wastewater management and processing.
The basic function of an electromagnetic meter is to measure and record the volumetric movement of various types of fluids and liquids. These measurements are recorded in feet or meters per minute or second, depending on the type of meter and its calibration. Though these are the meters designed functions, the data they provide can also be used to produce other calculations.
The majority of the data that a magnetic flow meter provides is ascertained by the meter. When combined with other devices, the meter is capable of supplying a variety of other readings and measurements.
Electromagnetic flow meters measure the movement and consumption of a liquid substance in a pipeline through the use of a magnetic field. The readings of the meter are converted into flow capacity parameters and transmitted to a control system.
Though electromagnetic meters are designed for volumetric flow measurement, they can also be used to measure mass. If the density of the fluid is entered into the meter, it can use the data to calculate mass flow. For the meter to make these calculations, the density value must remain stable and constant.
The key to the data collected by a magnetic flow meter is the positioning of the sensor that is placed inline to the movement of the flow. As the fluid passes through the sensor, it measures the induced voltage generated by the fluid's movement. The voltage generated by the sensor is sent to the transmitter that converts the information into a measurement of the flow.
This seemingly simple process provides valuable data regarding the volumetric flow, which is used to determine usage, fluid control, and other factors required for use of the fluid. The calculation and data from the meter provides engineers and management essential information regarding quantities being produced or used.
The use of magnetic flow meters is based on their many benefits as a non-invasive method for measuring and calculating fluid movement. The fact that the meter does not affect the pressure in the pipeline is a significant reduction in piping costs. Once a magmeter is installed, there is little need or concern for its maintenance since it does not have any moving parts and accurately functions regardless of the type of liquid being monitored.
There are an endless number of benefits regarding the use of magnetic flow meters. Every user has found them to be one of the most helpful and reliable instruments for fluid measurement. The central and primary positive factors are the meter's low cost and accurate data.
The measurements and readings from the meter can be instantly transferred from the meter to a computer. The provided data can be analyzed and examined to determine liquid consumption, possible leaks in the system, and as a method for predicting future consumption and usage.
An important advantage of magmeters is the absence of moving parts. Meters and equipment with moving parts are subject to wear, use, and deterioration. By not having any moving parts, a magnetic flow meter lasts longer, which provides a cost savings in the long run. The lack of wear and no moving parts have led to more and more fluid movement industries turning to magnetic flow meters.
The electrodes and sensors are placed in-line and do not affect the flow of the fluid to be measured. Without moving parts, the meter can complete its function without the need for maintenance or repair.
Magnetic flow meter manufacturers take pride in the durability and quality of their products. Every meter is tested multiple times to determine if there will be any future wear or degradation of the quality of the meter. Again, this leads to cost savings since the need to replace the meter is removed. Electromagnetic meters are a reliable and stable solution for long term measurement of conductive liquids.
Another cost saving aspect of magnetic flow meters is their low power usage. On average, a magnetic flow meter has a power usage of 15 watts.
Magnetic flow meters can measure the flow rate of any conductive substance regardless of the liquids acidity or corrosiveness. To enhance the performance of magnetic flow meters, manufacturers make a special effort to line the sensor measuring section of the meter with abrasion and corrosion resistant liners, which expands their use to include toxic and harmful substances.
Unlike other flow measurement methods, magnetic flow meters are unaffected by the properties of the flow being measured. Temperature, density, viscosity, and pressure do not have an affect on the meter's ability to take its readings. Once it is calibrated, it can measure the conductivity of any fluid without any concern for additional adjustments or calibrations.
As with other factors, magnetic flow meters are unaffected by changes in the flow rate. Whether the meter is 0.125 of an inch in diameter or up to 10 cubic feet, it is able to measure any of the possible flow rates produced by a fluid. Very low or high flow rates do not affect the meter‘s ability to perform and produce accurate data.
Aside from their adaptability to flow rates, magnetic flow meters are able to measure fluids that have laminar, turbulent, and transitional flows without the need to make adjustments or recalibrations.
One of the liabilities of other forms of flow meters is their inability to perform when the direction of the flow changes. In most cases, they must be adjusted and recalibrated to fit the new conditions. This is not true for magnetic flow meters, which can measure the flow rate regardless of its direction. This particular factor saves time and labor when rapid and on the spot changes are necessary.
A major use for magnetic flow meters is their use for measuring the flow rate of dirty, thick, and viscous substances. The ability of a magnetic flow meter is not influenced by a fluid‘s inconsistencies or contaminants. As long as the fluid is conductive, the meter will be able to measure its flow rate regardless of its consistency, thickness, or having solid matter.
As much of a benefit the low pressure of a magnetic flow meter is to the condition of the pipeline. A secondary and important factor is the lack of a pressure drop in the line, which minimizes any effect that can damage the pumping mechanism. This single factor is a significant cost savings regarding pump operation and performance.
Magnetic flow meters come in sizes and diameters to fit any application with the extra benefit of being able to be adapted and adjusted to fit any pipe diameter without losing efficiency. The ability of magnetic flow meters to be sized and adjusted to fit a variety of pipe sizes has been a major factor in their popularity.
One of the concerns regarding the installation of a magnetic flow meter may be the initial cost since specially designed meters can be expensive. Though this may have an influence regarding the use of magnetic flow meters, it must be examined from the perspective of longevity and time of use. Unlike meters with moving parts, magnetic flow meters make up for their initial cost in their performance, lack of maintenance, accuracy of their readings, and lifetime of use. Each of these factors significantly reduce the initial investment.
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