Flow Detectors
OTHER FLOW METERS
Summary
The basic construction and theory of operation of rotameters, nutating disks, anemometers,
electromagnetic flow meters, and ultrasonic flow equipment are summarized below.
Other Flow Meters Summary
Rotameter
Consists of a metal float and a conical glass tube
Tube diameter increases with height
High density float will remain on the bottom of tube with no flow
Space between the float and the tube allows for flow past the float
As flow increases, the pressure drop increases, when the pressure drop is
sufficient, the float rises to indicate the amount of flow
Nutating Disc
Circular disk which is attached to a central ball
A shaft is fastened to the ball and held in an inclined position by a cam, or roller
Fluid enters an opening in the spherical wall on one side of the partition and
leaves through the other side
As the fluid flows through the chamber, the disk wobbles, or executes a nutating
motion
Hot-Wire Anemometer
Electrically heated, fine platinum wire immersed in flow
Wire is cooled as flow is increased
Measure either change in wire resistance or heating current to determine flow
Electromagnetic Flowmeter
Magnetic field established around system pipe
Electromotive force induced in fluid as it flows through magnetic field
Electromotive force measured with electrodes and is proportional to flow rate
Ultrasonic Flow equipment
Uses Doppler frequency shift of ultrasonic signals reflected off discontinuities in
fluid
Rev. 0
Page 11
IC-04
