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Insertion Magnetic Flow Meter
Magnetic flow meters use Faraday's law to measure the flow. The flow of the conducting fluid is cutting the lines of force generated by a coil, through which current flows. Thus the flow of conducting fluid induces EMF, which is sensed by the electrodes. This induced EMF is proportional to flow.
The available magnetic flow meters are of two types, viz. full bore and insertion. Full bore flow meters, as the name suggests are installed in the pipe line itself, and the bore of the magnetic flow meter is equal to the pipeline internal diameter. Insertion type magnetic flow meters are inserted in the pipeline through a nozzle similar to the nozzles used for installation of thermocouples etc. Both are essentially velocity measuring devices. Full bore magnetic flow meter measures the velocities across the pipe line cross section and therefore gives the average value of the flow. Insertion magnetic flow meters measure the velocity at a particular point and then this reading is extrapolated to the entire pipeline cross sectional area.
Normally the point of insertion is either the pipe line center or the point of average velocity. The point of average velocity is not easy to locate and moreover could shift with the changes in Reynolds numbers. The center is fixed but it is the point of maximum velocity from which the average velocity has to be computed. The flow is the product of average velocity and the cross sectional area of the pipe. Thus if the pipe is not uniform in diameters i.e. if it is slightly elliptical there will be error in the flow measurement. This is valid for all devices measuring flow based on the velocity measurement.
The proposed insertion type magnetic flow meter measures velocity at four different locations in the pipe line and averages the same to get the average velocity. The pipe line cross section is divided in four areas having equal flow and thus the points at which the velocity is measured are located on the basis of average velocity in these four areas. This is expected to give measurement accuracy to the extent of 1 % as compared to the accuracy value of 3 % of the conventional insertion type magnetic flow meter at a nominally extra price. It is also possible to measure at six or eight points instead of four points to get a better average value. The shape of the sensor can also be modified suitably to avoid the problems faced, when the sensor is used for dirty water service.
The applications are for all conducting fluids. This becomes more cost effective for higher pipe sizes where a full size magnetic flow meter is not cost effective.
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The available magnetic flow meters are of two types, viz. full bore and insertion. Full bore flow meters, as the name suggests are installed in the pipe line itself, and the bore of the magnetic flow meter is equal to the pipeline internal diameter. Insertion type magnetic flow meters are inserted in the pipeline through a nozzle similar to the nozzles used for installation of thermocouples etc. Both are essentially velocity measuring devices. Full bore magnetic flow meter measures the velocities across the pipe line cross section and therefore gives the average value of the flow. Insertion magnetic flow meters measure the velocity at a particular point and then this reading is extrapolated to the entire pipeline cross sectional area.
Normally the point of insertion is either the pipe line center or the point of average velocity. The point of average velocity is not easy to locate and moreover could shift with the changes in Reynolds numbers. The center is fixed but it is the point of maximum velocity from which the average velocity has to be computed. The flow is the product of average velocity and the cross sectional area of the pipe. Thus if the pipe is not uniform in diameters i.e. if it is slightly elliptical there will be error in the flow measurement. This is valid for all devices measuring flow based on the velocity measurement.
The proposed insertion type magnetic flow meter measures velocity at four different locations in the pipe line and averages the same to get the average velocity. The pipe line cross section is divided in four areas having equal flow and thus the points at which the velocity is measured are located on the basis of average velocity in these four areas. This is expected to give measurement accuracy to the extent of 1 % as compared to the accuracy value of 3 % of the conventional insertion type magnetic flow meter at a nominally extra price. It is also possible to measure at six or eight points instead of four points to get a better average value. The shape of the sensor can also be modified suitably to avoid the problems faced, when the sensor is used for dirty water service.
The applications are for all conducting fluids. This becomes more cost effective for higher pipe sizes where a full size magnetic flow meter is not cost effective.
back...