Surface Acoustic Waves (SAW)

Basics

The abbreviation “SAW” stands for “surface acoustic waves”. It therefore means waves that propagate along surfaces. The type of propagation is comparable with acoustic wave propagation in seismic activities, such as an earthquake.

These surface waves are artificially generated in miniaturised form by means of SAW technology. In the case of the FLOWave flowmeter, these surface waves now propagate along the sensor measurement tube, and these acoustic surface waves can then be used to measure the flow of fluids. Bürkert has had the use of SAWs for flow measurement patented.

Declaration of the SAW measurement principle

The surface waves are generated by interdigital transducers (IDTs for short). These are placed at set areas of the FLOWave measurement tube. An electrical impulse emitted with a frequency within the 1 MHz range excites the IDTs, generating SAWs.

A wave front propagates along the tube surface, as well as through the medium, from the initial centre of excitement that arises. The wave front is also “reflected” by the measurement tube and shifts through the medium in the pipe several times.

Play Video

Detailed description of the process shown in the video

Determination of measured values

The time difference of the propagation period of the measurement signal in the forward direction and backward direction of the flowing fluid is proportional to the flow velocity. The volume flow can be calculated based on these measured values. The temperature is measured by an integrated digital temperature sensor. 

Based on the parameters of temperature, density, flow velocity and volume flow that are determined this way, it is possible to determine the mass flow rate as well.

Further special functions derived from the process values (differentiation factor, acoustic transmission factor, concentration of certain mixtures) offer additional information on the fluid in question, such as the detection of gas bubbles or solid parts as well as recognition of media changes.

Advantages

Based on the use of SAW technology, various advantages are created for the industrial flow measurement of fluids:

Only one pipe (316L / 1.4435 stainless steel)

• No additional parts that come into contact with media
• Contactless & hygienic measurement
• No moving parts – 100% wear-free
• No narrowing, meaning no pressure drop / loss in pressure

Multi-parameter measurement

• A single device for determining several parameters
• Less effort for device / asset management
• Seamless monitoring
• Special functions for recognising gas bubbles, solid parts or media changes

Robust & industrial-suited

• Interference from plant vibrations is eliminated by the high excitation frequency of 1 MHz.
• No influence on measurement by magnetic or electrical effects
• The measurement is not dependent on the conductivity of the medium and is possible even if this is low or not existent

Compact & light

• Reduced space requirements allows for the downsizing of machines and systems
• Simple installation and commissioning
• No additional brackets or reinforcements required
• Minimal maintenance required, e.g. at prescribed maintenance intervals

Application examples

SAW technology is used particularly in hygiene-sensitive environments, in the pharma & biotech and food & beverage sectors. Hundreds of customers have trusted innovative FLOWave flow measurement for years - whether it is for ensuring the quality of pharmaceuticals, the detection of media changes, for flow measurement in WFI circuits or for the dosing of edible oil.

Further information as well as examples of successfully implemented FLOWave projects for leading, innovative companies in the pharmaceutical and food industries can be found on the following website.