Rotameter
From Wikipedia, the free encyclopedia
A Rotameter is a device that measures the flow rate of liquid or gas in a closed tube. It is occasionally misspelled as 'rotometer'.
It belongs to a class of meters called variable area meters, which measure flow rate by allowing the cross sectional area the fluid travels through to vary, causing some measurable effect.
A rotameter consists of a tapered tube, typically made of glass, with a float inside that is pushed up by flow and pulled down by gravity. At a higher flow rate more area (between the float and the tube) is needed to accommodate the flow, so the float rises. Floats are made in many different shapes, with spheres and spherical ellipses being the most common. The float is shaped so that it rotates axially as the fluid passes. This allows you to tell if the float is stuck since it will only rotate if it is not. Readings are usually taken from the top of the float. Some manufacturers may use a different standard, so it is always best to check the documentation provided with the device.
Note that the 'float' does not actually float in the fluid: it has to have a higher density than the fluid otherwise it will float to the top even if there is no flow.
Advantages:
- A rotameter requires no external power or fuel, it uses only the inherent properties of the fluid, along with gravity, to measure flow rate.
- A rotameter is also a relatively simple device that can be mass manufactured out of cheap materials, allowing for widespread use in places such as third world countries.
Disavantages:
- Due to its use of gravity, a rotameter must always be vertically oriented and right way up, with the fluid flowing upwards.
- Due to its reliance on the ability of the fluid or gas to displace the float, the graduations on a given rotameter will only be accurate for a given substance. The main property of importance is the density of the fluid. Either separate rotameters for different substances must be used, or the read out adjusted.
- Rotameters normally require the use of glass (or other transparent material), otherwise the user cannot see the float. This limits their use in many industries to benign fluids, such as water.
- Rotameters are not easily adapted for reading by machine: although magnetic floats that drive a follower outside the tube are available.
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The first variable area meter with rotating float was invented by Karl Kueppers in Aachen in 1908. This is described in the german patent 215225. Felix Meyer found the first industrial company "Deutsche Rotawerke GmbH" in Aachen recognizing the fundamental importance of this invention. They improved this invention with new shapes of the float and of the glas tube. Kueppers invented the special shape for the inside of the glas tube that realized a symmetrical flow scale. The brandname Rotameter (Rotamesser) traced one's descent from the founded company name "ROTA".
The company "Deutsche Rotawerke GmbH" was converted into "ROTA Apparate- und Maschinenbau Dr. Henning KG" in 1939 and moved to the location De-79664 Wehr (Baden). The company invented further types of the Rotameter in the following years. Also the short-stroke Rotameter with a metering tube completely made of metal.
The company "ROTA Apparate- und Maschinenbau Dr. Henning KG" was converted into "ROTA YOKOGAWA GmbH" in 1993 and is therefore now a member of the YOKOGAWA group.
