Variable Area Flow Meter

-Interesting facts about a reliable, flow measuring principle-

About the page

This is an information page about flow measurement with variable area flowmeters. My many years of experience in the field of measurement and control technology are recorded here. I accept no liability for incorrect information or errors and would be pleased to receive further suggestions and requests for additions.
Please also visit my information page about Pt100 temperature sensors:

Harald Peters


Links to selected flow meter manufacturers and suppliers.

ABB Asea Brown Boveri Ltd
Brooks Instrument GmbH
Heinrichs Messtechnik GmbH
Georg Fischer GmbH
GHM Messtechnik GmbH
Heinrichs Messtechnik GmbH
KROHNE Messtechnik GmbH
Mecon GmbH
Meister Strömungstechnik
STÜBBE Gmbh & Co. KG
Vögtlin Instruments GmbH

General information

Durchflussmesser Glas
Durchflussmesser Glas
Durchflussmesser Metall

Flow meters based on the variable area principle, have been used for more than 100 years as cost-effective and reliable measuring devices for measuring the flow of liquids, gases or vapours in pipelines.
Standard devices consist of a conical measuring tube made of glass or transparent plastic in which a float adjusts to a certain height in the measuring tube depending on the flow rate.
The actual flow rate can then be read directly from a scale attached to the measuring tube.
For higher operating pressures or opaque fluids, conical metal tubes are used. The position of the float is transmitted by magnetic force to a display unit mounted on the unit without contact.
Electrical transmitters with Hart, Profibus, or other protocols built into the display unit make remote transmission of the measured values possible.
Additional reed or inductive contacts are used to monitor the flow values.
No electrical supply is required for pure measurement.

Advantages: Disadvantages:


History of Variable Area Flow Meter

The first mention of the measurement of flow in a conical pipe with a float was made by the American Edmund A. Chameroy, who applied for a patent for his invention in 1868.
In the following 15 years, further patent applications were filed in England and Germany for designs with constructive improvements.
A decisive discovery was made in 1908 by Karl Küppers (1874-1933) in Aachen (Germany).
While building floats for monitoring burner gases, he discovered that a rotating float significantly improves the accuracy and reliability of the measurement. He applied for a patent for this discovery at the Reichspatentamt (Germany) in the same year with the number DE21225C (
The rotation of the float was realised by inclined notches on the float head.
Felix Meyer recognised the importance of this invention and founded the "Deutsche Rotawerke GmbH" in Aachen (Germany). He optimised the float shape, produced and marketed the devices industrially as Rotameter®.
The company moved to Wehr in Baden in 1944 and still produces floats and other flowmeters there today under the name Rota-Yokogawa, as a subsidiary of the Japanese company Yokogawa.
Rotameter® is a registered term of the Rota-Yokogawa company.
In the meantime, variable area flowmeters are produced and marketed worldwide by many companies in a wide variety of designs.
Estimated market volume worldwide, several hundred thousand units per year.