Sensing oil in compressed air

When compressed to a smaller volume, air attains higher-than-atmospheric pressure that makes it useful in many industrial and domestic applications. That force per unit area can be used to impart motion in pneumatic tools. It can also atomise or spray substances such as automotive coatings, provide aeration for oxidation in pharmaceutical processes or clean electronics during production.

These and other high-end applications require very-high–purity compressed air. Oil contamination is a pressing problem and there is currently a lack of any reliable, highly sensitive, online sensor system to deal with it. EU-funded scientists are providing the much-needed solution with a new real-time sensor system through the project 'Detection of oil in compressed air' (DOCA). It will detect oil in all its forms (liquid, aerosol and vapour), ensuring compliance with regulations and eliminating the risks and liabilities associated with non-conformance.

Investigators have chosen optical spectroscopy. It is the most promising technology to guarantee extremely high sensitivity (meeting ISO-8573 Class I standards of air quality), repeatability, robustness to interference and stable calibration. The sensor platform will consist of three units: the sampling system, the optical spectroscopy unit, and the electronics and software.

The sampling system has been designed and allows for non-invasive monitoring of oil contamination in compressed air flow. The optical spectroscopy unit, photoacoustic spectroscopy, is progressing well. The technology relies on the emission of sound (a pressure wave of thermal expansion) in response to absorption of electromagnetic energy (light). It is relatively simple and inexpensive yet highly sensitive. Current development is focused on optimising the technique and potentially increasing sensitivity by a factor of 10.

Preliminary results support achievement of a Class I or better sensor. A patent is expected. Finally, electronics for the sensor have been specified and software written.

DOCA technology for online and real-time identification of oil contamination in compressed air will have major impact on both the costs and effectiveness of monitoring. A commercial product is expected to follow shortly after completion of the project.