Positive Displacement Flowmeters, which employ one of the oldest-known flow measurement techniques, are widely used in industry and have one of the largest install bases of any flow meter technology. Positive Displacement Flowmeters feature two precisely machined rotating members inside a measuring chamber of known volume which may be used to accurately determine volumetric flow rate as a function of the rotors' velocity. A more detailed discussion of the principle of operation can be found at:http://www.smartmeasurement.com/flow-meters/positive-displacement/measuring-principle
The advantages that the Positive Displacement Flowmeter provides over other technologies are numerous. These advantages include high accuracy (up to 0.1% of reading), excellent repeatability, wide turndown ratios, high temperature operation, high viscosity operation, no upstream or downstream straight pipe requirement, the ability to be used with mechanical registers which require no electrical power, and readings which are immune to changes in viscosity. This combination of features and advantages makes the PD meter an ideal choice for applications that can be found in many different industries including food & beverage, paint & coatings, oil & gas, and fluid power.