Flow is one of the crucial parameters measured in process industries and water treatmentplants, amongst other applications. For example, in water treatment plants where filtration equipment is cleaned periodically, a predetermined volume of water has to be pumpedthrough filters. The GPM(Gallons per minute) value is multiplied by the duration of thecleaning process to measure the amount of water used for cleaning. A similar principle isused for measuring the amount of chemicals such as acids or caustic in a ClP(Clean in placeprocess. Accurate measurements of these chemicals ensure a successful cleaning operationwithout damaging equipment.

More often than not, flowmeters use indirect measurement principles to calculate the flow offluids. In these cases, a change in a physical parameter such as temperature or pressure ismeasured. This measured change is then used in a formula for calculating the flow of theliquid or gas. Some types of flowmeters, such as rotameters, have a local analog readout butmost have a way of sending an electrical signal to a remote location in addition to a digitaldisplay.

Magnetic flowmeters can only be used to measure the flow rate of conductive liquids such aswater. As shown below, when the process liquid flows through a conduit of the flow meter, itis exposed to a magnetic field. An effect similar to Faraday's law occurs inducing a voltage inthe flow meter. The electrodes placed in the flow meter's walls measure the voltagedeveloped. This induced voltage increases with an increase in the flow. Based on the inducedvoltage and the size of the tube, the flow rate is calculated by the flow meter.