Flow DetectorsOTHER FLOW METERSThe float should stay at a constant position at a constant flow rate. With a smooth float,fluctuations appear even when flow is constant. By using a float with slanted slots cutin the head, the float maintains a constant position with respect to flow rate. This typeof flow meter is usually used to measure low flow rates.DisplacementMeterIn a displacement flow meter, all of the fluid passes through the meter in almost completelyisolated quantities. The number of these quantities is counted and indicated in terms of volumeor weight units by a register.NutatingDiskThe most common type of displacement flow meter is the nutating disk, or wobble platemeter. A typical nutating disk is shown in Figure 7.Figure 7 Nutating DiskThis type of flow meter is normally used for water service, such as raw water supply andevaporator feed. The movable element is a circular disk which is attached to a centralball. A shaft is fastened to the ball and held in an inclined position by a cam or roller.The disk is mounted in a chamber which has spherical side walls and conical top andbottom surfaces. The fluid enters an opening in the spherical wall on one side of thepartition and leaves through the other side. As the fluid flows through the chamber, thedisk wobbles, or executes a nutating motion. Since the volume of fluid required to makethe disc complete one revolution is known, the total flow through a nutating disc can becalculated by multiplying the number of disc rotations by the known volume of fluid.Rev. 0 Page 9 IC-04
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