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E-Zine January 2011Some level measurement systems measure the level of the material. For example, float location and the amount that a capacitance probe is covered with material are indicative of the material level. However, many level measurement systems inherently do not measure level --- they infer level. Most notable is hydrostatic level measurement that infers level using fluid density. Whereas level measurement is (theoretically) supposed to determine the location of an interface, hydrostatic measurement measures the effective mass of the fluid and infers the location of the interface. Therefore, the (inferred) level measurement will vary when the density of the material in the vessel changes. Other examples of inferred level measurement include ultrasonic and radar level measurement systems where the measured distance from the sensor to the material is used to infer the level of the material. The most common application of level measurement systems is to determine the inventory of a contained material. Although this may be desirable for the efficient operation and safety of the process, level measurements are also used for accounting purposes. Excerpted from The Consumer Guide to Non-Contact Level Gauges ISSN 1538-5280 |
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