Magnetic flow meter

Measurement by Electromagnetic Effects. The magnetic flow meter is a device that measures the potential developed when an electrically conductive flow moves through an imposed magnetic field. The voltage developed is proportional to the volumetric flow rate of the fluid and the magnetic field strength. The process fluid sees only an empty pipe so that the device has a very low pressure drop. The device is useful for the measurement of slurries and other fluid systems where an accumulation of another phase could interfere with flow measurement by other devices. The meter must be installed in a section of pipe that is much less conductive than the fluid. This limits its appHcabiHty in many industrial situations. 

Magnetic flow meters are sometimes utilized in corrosive Hquid streams or slurries where a low unrecoverable pressure drop and high rangeabiHty is required. The fluid is required to be electrically conductive. Magnetic flow meters, which use Faraday s law to measure the velocity of the electrically conductive Hquid, are relatively expensive. Their use is therefore reserved for special situations where less expensive meters are not appropriate. Installation recommendations usually specify an upstream straight mn of five pipe diameters, keeping the electrodes in continuous contact with the Hquid. 

Hydrochloric acid is capable of evolving hydrogen on reaction with many common metals. A magnetic flow meter is reported as exploding after the acid reached the electric amplifier compartment. 

In this chapter we will illustrate and analyze some of the more common methods for measuring flow rate in conduits, including the pitot tube, venturi, nozzle, and orifice meters. This is by no means intended to be a comprehensive or exhaustive treatment, however, as there are a great many other devices in use for measuring flow rate, such as turbine, vane, Coriolis, ultrasonic, and magnetic flow meters, just to name a few. The examples considered here demonstrate the application of the fundamental conservation principles to the analysis of several of the most common devices. We also consider control valves in this chapter, because they are frequently employed in conjunction with the measurement of flow rate to provide a means of controlling flow. 

Magnetic finishing drums, 15 446 Magnetic flocculation, 16 639 Magnetic flow meters, 20 681 Magnetic flux, exponents of dimensions, 8 585t... 

Magnetic flow meters are seldom used, and often special constructions are required. 

Magnetic flow meter 400 30 1 1 % of span No pressure loss in the device, suitable for slurries... 

This chapter discusses the unit operations of flow measurements and flow and quality equalizations. Flow meters discussed include rectangular weirs, triangular weirs, trapezoidal weirs, venturi meters, and one of the critical-flow flumes, the Parshall flume. Miscellaneous flow meters including the magnetic flow meter, turbine flow meter, nutating disk meter, and the rotameter are also discussed. These meters are classified as miscellaneous, because they will not be neated analytically but simply described. In addition, liquid level recorders are also briefly discussed. 

Quite a number of technologies are available for measuring volumetric flow rates. These include differential pressure transmitters, vortex meters and magnetic flow meters. Each has its advantages and disadvantages. 

Flow. Prefer coriolis, vortex, or magnetic flow meters over orifice or venturi. Keep fluid velocity >0.3 m/s. 

Flow. Nonintrusive sensors that can be maintained at the process temperature are ideally suited to measure the flow rate of feed and product streams. Magnetic flow meters are suitable and inexpensive choice for aqueous streams. Organic streams with low dielectric constants require a vibrating tube mass flow meter to satisfy these criteria. Although commonly installed, flow meters that operate by inducing a pressure drop proportional to the flow rate present restrictions for solids accumulation that may alter the calibration. An alternative approach is to monitor the rotational speed of a positive displacement pump. Accuracy of this method is subject to wear and tolerances in the pump. 

Flow prefer coriolis, vortex or magnetic flow meters over orifice or venturi. Keep fluid velocity > 0.3 m s" Expected error orifice meter, +1-5% of full scale coriolis, +0.2% of full scale magnetic, +0.5-1% of full scale venturi, +0.25-3% of full scale. 

Magnetic flow meters are the preferred choice for brine feed flow measurement. If the saturator pump tank level is controlled by throttling the brine to the treatment tanks, as in Fig. 11.3a, the measurement shown in Fig. 11.4 gives the net brine flow through the system. It is used to detmnine the quantities of the treatment chemicals to be added. If the tank level control is through the recycle of the clarified brine, as in Fig. 11.3b, measurement of the recycle flow as well as the feed flow allows calculation of the net feed by subtraction. The resultant value can then be used to control the rates of addition of the treatment chemicals. The brine flow signal in Fig. 11.4 does not reflect the latter approach. 

A PTFE-lined magnetic flow meter measures the brine feed to the cell room. In a plant with a ratio-controlled anolyte recycle, this flow rate also can furnish the primary flow signal. The recycle anolyte stream returns to the brine feed header downstream of the pressure control valve. A PTFE-lined magnetic flow meter with platinum electrodes measures its flow. The control valve downstream of the flow meter should be a butterfly valve fully lined with PTFE. This valve should close upon rectifier failure. 

The most common product caustic flow instrument is a PTFE-lined magnetic flow meter with nickel electrodes. The flow signal should be integrated to measure total production. A Coriolis mass flow meter, also nickel, will give more precision if desired. Two mass flow meters can be used in parallel if one is too small to handle the flow. Again, flow from the system is recorded and integrated to provide a measure of the production rate. 

The caustic flow to the electrolyzer feed header is measured and monitored to ensure that there is always a flow to the cells. Magnetic flow meters are standard. The low-flow switch depicted in Fig. 11.53 starts a delay timer when it trips. After the delay set on the timer, the rectifiers will shut down. If the caustic flow recovers in time, the timer resets automatically. 

Principle magnetic flow meters are based on Faraday s law, which says that the speed of a conductor is proportional to the voltage induced in a magnetic field. The fluid should be conductive. 

The magnetic flow meter is used for liquid measurement, but generally requires only a minimum straight run upstream piping equal to the pipe diameter. The magnetic flow meter will not operate effectively in a fluid that has an electrical conductivity less than 10 micromho. 

Intermediate sodium is circulated through the shell-side of the IHX and the shell-side of the SG by two EM pumps, each located in the cold leg of the loop in the SG facility. The internal EM pumps— pumps with no moving parts that move conductive fluids by way of a magnetic field—circulate the molten sodium through the reactor core and then to the IHTS. Permanent magnet flow meters are located in the cold leg to monitor sodium flow in the loop. 

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