flowmeter:
(Magnetic mass flow meter)
This type of rigging measures the amount of flow with high accuracy by using the law of electromagnetic induction and the changes of the magnetic eruption based on the flow rate of the fluid.
This method of flow measurement is used in fluids that have conductive and electrical properties, and in services that do not have this feature, the fluid flow measurement will not be done correctly.
With this account, it will be used only in liquid KH fluids with a suitable conductivity coefficient.
Function of electromagnetic flowmeter:
This flowmeter includes a pair of magnetic poles, which will create a field in front of the fluid flow path using electric voltage.
Also, a pair of electrodes are used around the fluid flow path to receive the positive and negative electrons of the passing fluid.
Considering the conductivity of the passing fluid, it is necessary to isolate both electrodes from each other with insulation such as Teflon, hard rubber or PVC.
This type of lining is used inside the fluid flow path.
The measurement accuracy of this equipment is generally from 0.5% to 0.75%, and also considering the structure and performance in general, it will not have a size limit. This measurement method does not create any turbulence inside the tube.
For the same reason, calculations of upstream and downstream ranges will not have a place in this equipment.
According to the existing standards regarding the measurement of fluid flow, there are requirements for installation, including compliance with the distance of the equipment with tools that will create noise.
Equipment such as electric motors andIn the manufacturing technology of magnetic flowmeter, a method is used that reduces the amount of ambient noise on the equipment to a minimum. In this way, the polarity of the magnetic poles is shifted at every moment, and if an unwanted voltage is applied to the poles from the output part, it will be ineffective in measuring the fluid flow.
For the same reason, a separate power source is used to supply voltage, which is generally alternating voltage.
This heating is usually used in the temperature range up to 150 degrees Celsius.
Choosing the type of electrodes:
For liquids that are not corrosive, stainless steel is usually used.Because the liquids are corrosive, the following items can be used according to the chemical properties of the liquid:
stainless steel some nickel platinum platinum / iridium tantalum alloys.
Liner selection:
From there, the basis of the performance of magnetic flowmeters is to create a magnetic field and measure the induced voltage based on Faraday's law.
If so, the magnetic field created by the fluid is disrupted and a short circuit occurs. In the same way, if the inner surface of the pipe is conductive, this will also cause a short circuit of the electrodes. Therefore, the magnetic flowmeter is supposed to be installed at that point in the pipeline, it must be made of materials.
non-magnetic such as stainless steel, also the liner should be made of insulating materials.The liner must be selected according to the application and be resistant to the following factors: temperature, pressure, abrasion, erosion and chemical corrosion. Also, linear materials are generally used for flowmeters
and they are as follows:
Teflon (PTFE).
Suitable for the temperature range of -50 to 200 degrees Celsius,
very good resistance to erosion caused by fine particles, resistant to most bases and acids.
The energy consumption is relatively low and can be used for some models with less than 20 watts.
These types of flowmeters are non-shrink mechanical and can be equipped with wear-resistant coatings to make them effective for measuring other erosive fluids.
Their measurement range is very wide and they can measure very low and very high flow values with a minimum diameter of approximately 0.125 inches and a maximum volume of up to 10 cubic feet. Also, if we pay attention to Faraday's law, we can see that the fluid properties such as molecular mass and (u=k * B * D * V) do not have much effect.
This means there is a limitation in the use of this flowmeter in different areas It doesn't exist, and the only expectation we have is that the passing fluid is conductive.
For this reason, the data obtained from magnetic current meters are highly reliable and are used as standard data.
In some other cases, there are also limitations in the performance of this device.
Limitations of magnetic flowmeter:
Magnetic flowmeters will also have special problems in measuring flow.
These types of flowmeters are effective only on conductive liquids and cannot measure substances such as hydrocarbons and indirect gases.
On the other hand, the magnetic materials themselves may also cause problems, because hydrodynamic effects can change the natural current pattern and in this case the speed is not enough to create the induced voltage.
Considering their size and capacity, magnetic flowmeters can be relatively heavy, and the type with greater resistance to corrosion and wear can be more expensive.
Various sources stated that the standard temperature for magnetic flowmeter is 80 degrees Celsius.
Since increasing or decreasing the temperature can have a negative effect on the properties of the system and change the conductivity and other properties of the fluid, it is necessary to observe this temperature limit.
Applications of magnetic flowmeter:
Sewage water facilities, dam outlet, wells, pumping stations, urban and rural water supply lines, as well as measuring raw, drinking or purified water, waste water, sewage and
Chemical industry, acids, caustic soda, glue
Food industry, mineral water, milk, yogurt, buttermilk, molasses, beet juice, pharmaceutical industry
Metal / mineral industries
Paper/pulp industries
Marine industries
Water Pipe Network Industries
Water Management for Agricultural Irrigation Industries