Technical Guide
August 2007
Daniel® Valves In Load Rack Duty
TURBINE METER THEORY
The basic theory behind Daniel’s electronic liquid turbine meters is relatively simple. Fluid flow through the meter impinges upon the turbine blades which are free to rotate about an axis along the center line of the turbine housing. The angular (rotational) velocity of the turbine rotor is directly proportional to the fluid velocity through the turbine. These features make the turbine meter an ideal device for measuring flow rate.
The output of the meter is taken by an electrical pickoff(s) mounted on the meter body. The output frequency of this electrical pickoff is proportional to the flow rate. In addition to its excellent rangeability, a major advantage of the turbine meter is that each electrical pulse is also proportional to a small incremental volume of flow. This incremental output is digital in form, and as such, can be totalized with a maximum error of one pulse regardless of the volume measured.
The turbine meter and associated digital electronics form the basis of any liquid metering system. An expanding blade hanger assembly holds the turbine rotor in alignment with the fluid flow. The angle of the turbine blades to the stream governs the angular velocity and the output frequency of the meter. A sharper blade angle provides a higher frequency output. In general, the blade angle is held between 20º and 40º to the flow. Lower angles cause too low of an angular velocity and loss of repeatability, while larger angles cause excessive end thrust.
FLOW RATE IS PROPORTIONAL TO ANGULAR VELOCITY
Figure 3 below is a cross section of the internals of a Daniel turbine meter. Flow through the turbine meter is from left to right. The forward and rear suspension act as flow guides so that fluid motion through the meter is parallel to the meter centerline. Flow impinging upon the angular blade causes the rotor to spin at an angular velocity proportional to flow rate.
Figure 3 - Liquid Turbine Flow Meter Cross Section
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