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A flow meter is a device used to measure fluid or gas moving through it. The results returned by the meter may be expressed in one of two measurement values: volumetric flow or mass flow. Flow meter readings are returned in area- and application-specific units, with volumetric types producing readings in gallons, liters or cubic inches per second, while mass flow meters express their measurement in pounds or kilograms per second. There are several different general flow meter-type classifications, each of which is represented by a range of variants. Flow meters are used to meter the supply of gases and fluids in a wide range of industries and applications such as manufacturing plants, breweries, hospitals and domestic or industrial water supplies.
The metering of the flow of gases and fluids is an essential function in industrial process control, consumer billing systems and medical treatments. These measurements are typically achieved by placing a flow meter in series with the fluid or gas feed line. These meters then monitor the flow of material through them via the action of several different types of mechanisms. The calculated results may then be displayed on the meter itself or sent via an electronic output to a remote display or data storage facility. Although all flow meters measure real-time material flow across their assemblies, they do fall into two distinct types.
Both types of flow meter use different types of measurement units which, in themselves, differ according to global locations or industry types. Mass flow meters measure the physical mass or weight of the fluid or gas passing through the system. Volumetric flow meters measure the physical volume of material flow. Due to the compressibility of gases, their flow rates are often expressed as actual cubic feet or standard cubic meters per second.
Flow meter mechanisms are also grouped into several distinct categories including mechanical, pressure, optical and thermal types. The multiple-jet, Pelton wheel and Woltmann meters are all mechanical flow meter types which depend on the movement of a set of paddles, helical blades or impellers to measure the material flow. Pressure flow meters utilize venturis, pilot tubes and orifice plates to measure the pressure differentials used to calculate flow rates. Optical flow meters use lasers and photo detectors to measure dispersed light to calculate their flow results. Thermal meters make use of a system of heater elements and temperature sensors to calculate static and flowing temperature differentials in conjunction with known material characteristics to extrapolate flow values.
These flow metering devices are an essential part of many industrial process control applications where exacting material feed values is required. In these applications, the flow meter will typically interface with process controllers to adjust the flow of raw materials or end products. The flow meter is also widely used to calculated domestic and industrial consumer usage of water and gas for billing purposes.