Flow Measurement Will SAW–Technology Become the Perfect Wave for Flow Measurement?

Author / Editor: DOMINIK STEPHAN* / Dominik Stephan

New flow measurement technology – More often than not it is about inner values, but sometimes, it is also about what is lacking inside. That is the case with ultrapure water, and with a new flow measurement technology which works without any built-in sensors. How does it all come together? With the perfect wave, of course.

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(Pictures: Bürkert)

Sometimes the presence of valuable substances and trace elements is important — and sometimes the absence of any foreign contaminants is important, as with ultrapure water. Highly purified and virtually free of foreign matter, it is used for medicines, injections and as a process fluid in chemical analysis. Certain difficulties arise, however, when the question is to find out whether ultrapure water flows through a pipe or not — and if so, in what quantity. For the fluid, which is subject to the most exact demands and specifications, must not to be made impure.

An Overview of Flowmeters

A flow meter typically has a sensor in the pipe. Regardless of the principle on which the process works, measuring elements will come into contact with the process liquid at some point. There are exceptions to every rule, of course: Alternatives, such as magnetic inductive measurement (MID) or Coriolis mass flow meters, exist, but these too have their limitations.

MID measuring instruments or “mag meters” require a given minimum conductivity and a minimum liquid flow rate. They are just as ill equipped to cope with non-flowing liquids and high temperatures as they are with iron deposits. The low conductivity of ultra-pure water alone makes mag meters unsuitable for these applications.

That just leaves the Coriolis method — but these flow meters are extremely complex, large and expensive and therefore difficult to justify for certain applications. But wait — who says it is essential for a flow meter to have a sensor in the pipe?

From Lab to Production Line

“We were trying to find a gap in the market,” said Volker Erbe, product manager for sensors at Bürkert, “something which would send a clear message to customers that this would give them value added”. The specialists in fluid processes from Ingelfingen, Germany, embarked upon a radical rethink of the principle of flow measurement. On their journey they hit upon a process which works without any inbuilt fittings at all. Its secret? Surface acoustic waves — or SAW for short. These structure-borne sound waves spread out over a surface without penetrating very far into the material.