The reliability of Yokogawa’s Rotameter family of float-type flowmeters has been boosted by the development of a patented float-blocking indication system for the RAMC flowmeter that automatically detects any problems with the free movement of the float. Flowmeters based on the rotating-float principle offer the benefits of simplicity, minimal energy consumption, low cost and robustness. However, foreign particles in the medium being measured can cause the float to jam.

For many years flowmeters incorporated the float in a glass enclosure so it was easy to check visually whether the float was rotating correctly. Modern instruments, however, have the float rising and falling in a metal tube, with the float’s position transmitted by magnetic coupling to the indicator. Although this leads to a more robust instrument, it becomes inherently more difficult to check the working condition of the flowmeter.

The patented float blocking indication system is based on the fact that the float oscillates slightly when there is a flow. Software is incorporated in the transmitter to detect whether this basic movement is present. If the oscillation is absent, the software triggers an error signal and the output current is adjusted to fault-current level. Remote diagnostics then indicate that the instrument is no longer working correctly.

The Yokogawa Rotameter series RAMC and RAKD flowmeters are housed in stainless steel 1.4301 enclosures with the casting sealed to IP protection class IP66/67. The instruments carry hazardous area approvals including ATEX, FM, SAA and NEPSI, and the RAMC also complies with the SIL1 and SIL2 requirements.

In addition to providing a 4mA-20mA analogue signal for flow indication, minimum and maximum switching signals are available. HART and PROFIBUS PA are also available as interfaces for digital communication.

The Rotameter flowmeter was invented 100 years ago by the German engineer Karl Küppers. In the following year the company Deutsche Rotawerke – the forerunner of the present-day Rota Yokogawa – was founded. Since then the principles on which the Rotameter is based have not changed. Today, many millions of Rotameters make reliable measurements in plants in the chemical, pharmaceutical and food industries.