Impeller žowmeters, sometimes called paddle wheel meters, are one of the most commonly used žowmeter variety. œe impeller žow sensor is a direct o¥shoot of the old-fashioned undershot waterwheel. œey are a cost-e¥ective alternative to turbine meters and can be used in applications that are di¬cult to handle with other types of žow metering instruments. In their mechanical construction, they are usually very simple, with any sophistication residing in the electronics used to detect the rotation rate of the impeller and in the choice of materials of construction for chemical corrosion attributes of the metered žuids. œey are related toturbine meters in that both types use arotating mechanical element to produce the output signal. œey di¥er in the fact that the impeller meter has its rotary axis transverse to the žow stream, as opposed to the turbine meter axis, which is parallel thereto.