Application Cautions for Magnetic Flow Meters
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Application Cautions for Magnetic Flow Meters Do not operate a magnetic flow meter near its electrical conductivity limit because the flow meter can turn off. Provide an allowance for changing composition and operating conditions that can change the electrical conductivity of the liquid. In typical applications, magnetic flow meters are sized so that the velocity at maximum flow is approximately 2-3 meters per second. Differential pressure constraints and/or process conditions may preclude application of this general guideline. For example, gravity fed pipes may require a larger magnetic flow meter to reduce the pressure drop so as to allow the required amount of liquid to pass through the magnetic flow meter without backing up the piping system. In this application, operating at the same flow rate in the larger flow meter will result in a lower liquid velocity as compared to the smaller flow meter. For slurry service, be sure to size magnetic flow meters to operate above the velocity at which solids settle (typically 1 ft/sec), in order to avoid filling the pipe with solids that can affect the measurement and potentially stop flow. Magnetic flow meters for abrasive service are usually sized to operate at low velocity (typically below 3 ft/sec) to reduce wear. In abrasive slurry service, the flow meter should be operated above the velocity at which solids will settle, despite increased wear. These issues may change the range of the flow meter, so its size may be different than the size for an equivalent flow of clean water. |