The most common type of displacement flow meter is the nutating disk, or wobble plate meter. A typical nutating disk is shown in Figure A1. Figure A1 This type of flow meter is normally used for water service, such as raw water supply and evaporator feed. The movable element is a circular disk which is attached to a central ball.
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They operate by having a disc mounted to a central ball. When fluid enters the chamber, it causes the disc to wobble nutate , transferring the displaced volume to the register. Something to keep in mind, is that due to the nutating discs nature, the accuracy of this type of flow meter can be adversely affected by fluctuations in liquid viscosity.
Nutating Disc Flow Meters Liquid enters a precision-machined chamber containing a disc which nutates wobbles. The position of the disc divides the chamber into compartments containing an exact volume.
Liquid pressure drives the disc to wobble and a roller cam causes the nutating disc to make a complete cycle. This motion is translated into rotary motion by means of a ball and shaft, which is attached to the disc.
There are inherently more leakage paths in this design and it tends to be used where longer flow meter life is required rather than high performance; however, close clearances between the disc and chamber ensure minimum leakage for accurate and repeatable measure of each volume cycle. A disc attached to a sphere is mounted inside a spherical chamber. As fluid flows through the chamber, the disc and sphere unit nutates. The nutation causes a pin, mounted on the sphere perpendicular to the disc, to rock.
Each revolution of the pin indicates a fixed volume of liquid has passed. A mechanical or electromagnetic sensor detects the rocking of the pin and the flow is measured. How Sensor Picks up the reading — These flow meters may use a Hall sensor to sense the rotation and the same was converted into equivalent flow.
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Nutating Disc Meters
It consists of a precision machined chamber, a center ball, movable disc, and counter mechanism. The disc is pivoted at the geometric center, and it is allowed to nutate or wobble in a specially designed chamber. The controlled clearance between the disc and chamber ensures the proper sealing and minimum leakage. How nutating disc flow meter work The disc divides the chamber into two equal volume. In above fig, water enters at the left side of the eccentrically mounted disc. The liquid pressure sets the disc in motion, results in the quantity of liquid that enters left side of the chamber will be rolled out through the outlet.
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