History
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
(https://patents.google.com/patent/DE.
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.