Rotameter

A rotameter is a variable area flow meter used to measure the volumetric flow rate of liquids and gases. It consists of a tapered tube, typically made of glass or plastic, and a "float" (also known as a plummet or bob) which is suspended within the tube by the flow.

The fluid enters the rotameter from the bottom and flows upward, forcing the float to rise. The float rises until the upward force of the fluid flow equals the downward force of gravity acting on the float. The position of the float within the tube is directly proportional to the flow rate. A scale is marked on the tube, allowing the user to read the flow rate directly.

The tapered shape of the tube allows for a wider range of flow rates to be measured. At low flow rates, the float will rest at the bottom of the tube, where the area is smaller. As the flow rate increases, the float will rise higher into the tube, where the area is larger.

Rotameters are relatively simple, inexpensive, and easy to install and use. They do not require external power or signal conditioning. However, they are typically installed vertically and require a clear line of sight to read the flow rate. They are also sensitive to changes in fluid density and viscosity. Different floats and tube sizes are available to accommodate a wide range of fluids and flow rates. The accuracy of a rotameter is typically in the range of +/- 2% to +/- 5% of full scale.