A Flow Sensor or a Flow Meter, is a device used to quantify the volume of fluid passing through a point in a pipe. Reed Switch based flow sensors are built with a paddle having multiple magnets or a single multi-pole magnet that continuously triggers the reed switch to generate a square wave output that can be translated to volume of fluid.
Flow measurement is the quantification of bulk fluid movement. Flow can be measured in a variety of ways. The common types of flowmeters that find industrial application can be listed as below: a) Obstruction type(differential pressure or variable area) b) Inferential(turbine type) c)electromagnetic d)Positive-displacement flow meters accumulate a fixed volume of fluid and then count the number of times the volume is filled to measure flow. e)fluid dynamic(vortex shedding) f)Anemometer g)Ultrasonic H)Mass flowmeter(Coriolis).
Flow measurement methods other than positive-displacement flowmeters rely on forces produced by the flowing stream as it overcomes a known constriction, to indirectly calculate flow. Flow may be measured by measuring the velocity of fluid over a known area. For very large flows, tracer methods may be used to deduce the flow rate from the change in concentration of a dye or radioisotope.