The flow field inside an orifice flow meter

Orifice meters, the simplest form of obstruction or pressure-differential meter, is the most commonly used device for measuring volumetric flow rates. The popularity of the orifice meter can be attributed primarily to its simplicity and relatively low maintenance requirements. Orifice plates have been used as the standard fluid-metering device by the natural gas industry since the 1800s. In the U.S. natural gas industry alone approximately one million orifices are used. This paper describes the basic idea employed in the orifice meter, embodied in Bernoulli's principle. In this context, an orifice can be taken to be a generic term for any constriction in the flow. The pressure drop produced by the constriction will be directly related to the flow velocity. The orifice plate, on the other hand, is exactly what is implied. It is simply a hole drilled through a relatively thin flat plate. The orifice is inserted in the pipe perpendicular to the flow.