A rotameter is a device that measures the volumetric flow rate of fluid in a closed tube.

Rotameters Overview

  1. A rotameter requires no external power or fuel, it uses only the inherent properties of the fluid, along with gravity, to measure flow rate.
  2. A rotameter is also a relatively simple device that can be mass-manufactured out of cheap materials, allowing for its widespread use.
  3. Since the area of the flow passage increases as the float moves up the tube, the scale is approximately linear.
  4. Clear glass is used which is highly resistant to thermal shock and chemical action.

Rotameter Principle

A rotameter consists of a tapered tube, typically made of glass or metal with a ‘float’ (a shaped weight, made either of anodized aluminum or a ceramic), inside that is pushed up by the drag force of the flow and pulled down by gravity. The drag force for a given fluid and float cross-section is a function of flow speed squared only, see drag equation.

A higher volumetric flow rate through a given area increases flow speed and drag force, so the float will be pushed upwards. However, as the inside of the rotameter is cone-shaped (widens), the area around the float through which the medium flows increases, and the flow speed, and drag force decrease until there is mechanical equilibrium with the float’s weight.



Mass & Volumetric flow monitoring of most gases, liquids and steam

Measures four process variables with one process connection:

  • Mass flow rate/Volumetric flow rate

Easy to Install, lots of field installation options

Rugged, long-lasting design for the toughest applications


Pipe diameter:3/8″inch to 6″inch



Pressure rate:≤600 Bar



Ambient temperature:
Operating: -20° to 60°C
Storage: -40° to 65°C


Power supply:24VDC 100mA,3.6V Battery,Mechanical

Output signal:

  • 4-20mA
  • Pulse
  • User-definable pulse output for totalized flow

Digital communications: RS485, Hart

Hazardous-Area Location Enclosure

Flange TYPE

metal tube

circuit board

Calibration Device

Filed indicator



  • inline rotameter 1“ inch drawing
  • inline rotameter 1.5“ inch drawing


  • RS485 Protocol
  • Hart Protocol

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