The majority of all gas measurement used in the world today is performed by two basic types of meters, positive displacement and inferential. Positive displacement meters, consisting mainly of diaphragm and rotary style devices, generally account for lower volume measurement. Orifice, ultrasonic and turbine meters are the three main inferential class meters used for large volume measurement today. Turbines are typically considered to be a repeatable device used for accurate measurement over large and varying pressures and flow rates. They are found in a wide array of elevated pressure applications ranging from atmospheric conditions to 1440 psig.
Turbine meters have also become established as master or reference meters used in secondary calibration systems such as transfer provers. A significant number of both mechanical and electrical outputs and configurations have become available over the past 60 years of production.
This paper will focus on the basic theory, operating principles, performance characteristics and installation requirements used in turbine meter applications. A discussion of fundamental turbine meter terminology is also included.
An inferential style device derives or “infers” volumetric measurement using the concept of velocity. In the case of the turbine meter, the flowing gas velocity is represented by the rotation of the rotor itself. The speed or rotation
of the rotor is directly proportional to the rate of flowing gas.
Flowing gas enters the inlet of the turbine meter and is immediately directed through a smaller channel created by the annular passage between the body and nose cone (Illustration 1).