Tuesday, May 23, 2017

Variable Area Flowmeters (aka Rotameters) - How They Work

variable area flowmeter
Variable area flowmeter
(courtesy of Brooks Instrument)
A rotameter is one particular type of variable area flowmeter that measures flow by varying the cross-
sectional area a fluid or gas travels through in a closed tube.

Advantages
  • Requires no external power. 
  • Is a simple device that can be easily manufactured out of inexpensive materials. 
  • Linear scale. 
  • The clear glass tube is resistant to thermal shock and chemical reaction. 
Disadvantages
  • Must be mounted vertically, with designated top and bottom, and with the fluid flowing from bottom to top. 
  • Graduations on a given rotameter are only accurate for a given substance at a given temperature. Separate rotameters must be used for fluids with different densities and viscosities, or multiple scales on the same rotameter must be used. 
  • Resolution is relatively poor and gets worse near the bottom of the scale. 
  • Oscillations of the float and parallax lend to reduced accuracy. 
  • Difficult to automate - primarily a manual / visual device.