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Auto-calibration of ultrasonic lubricant-film thickness measurements

Reddyhoff, T., Dwyer-Joyce, R.S., Zhang, J. and Drinkwater, B.W. (2007) Auto-calibration of ultrasonic lubricant-film thickness measurements. Measurement Science and Technology, 19 (4). Art. No. 045402. ISSN 0957-0233

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The measurement of oil film thickness in a lubricated component is essential information for performance monitoring and design. It is well established that such measurements can be made ultrasonically if the lubricant film is modelled as a collection of small springs. The ultrasonic method requires that component faces are separated and a reference reflection recorded in order to obtain a reflection coefficient value from which film thickness is calculated. The novel and practically useful approach put forward in this paper and validated experimentally allows reflection coefficient measurement without the requirement for a reference. This involves simultaneously measuring the amplitude and phase of an ultrasonic pulse reflected from a layer. Provided that the acoustic properties of the substrate are known, the theoretical relationship between the two can be fitted to the data in order to yield reflection coefficient amplitude and phase for an infinitely thick layer. This is equivalent to measuring a reference signal directly, but importantly does not require the materials to be separated. The further valuable aspect of this approach, which is demonstrated experimentally, is its ability to be used as a self-calibrating routine, inherently compensating for temperature effects. This is due to the relationship between the amplitude and phase being unaffected by changes in temperature which cause unwanted changes to the incident pulse. Finally, error analysis is performed showing how the accuracy of the results can be optimized. A finding of particular significance is the strong dependence of the accuracy of the technique on the amplitude of reflection coefficient input data used. This places some limitations on the applicability of the technique. © 2008 IOP Publishing Ltd.

Item Type: Article
Copyright, Publisher and Additional Information: Copyright (c) 2007 IOP Publishing Ltd. This is an author produced version of a paper published in ' Measurement Science and Technology'. Uploaded in accordance with the publisher's self-archiving policy.
Keywords: Film thickness Reflection coefficient Tribology Ultrasound Computation theory Reflection Substrates Oil film thickness Self-calibrating routine Lubricants
Institution: The University of Sheffield
Academic Units: The University of Sheffield > Faculty of Engineering (Sheffield) > Department of Mechanical Engineering (Sheffield)
Depositing User: Mr Christopher Hardwick
Date Deposited: 18 Aug 2009 14:17
Last Modified: 08 Feb 2013 16:58
Published Version: http://dx.doi.org/10.1088/0957-0233/19/4/045402
Status: Published
Publisher: IOP Publishing Ltd
Refereed: Yes
Identification Number: 10.1088/0957-0233/19/4/045402
URI: http://eprints.whiterose.ac.uk/id/eprint/9163

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