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Determination of the uncertainty of typical airborne sound-measurements on automobile components
2008 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Measurements are performed daily in engineering praxis and the results often serve as a basis for the further development of products or business strategies. However, a measurement result is not complete without the statement of the measurement uncertainty since it provides information about the quality of the result and the measurement method. It makes it possible to estimate how reliable the results are. The purpose of this thesis is to find methods to determine the measurement uncertainty of common acoustic measurements for the development of automobile engine components as implemented in the international standard “Guide to the expression of Uncertainty in Measurement”. The measurements are restricted to airborne sound emission and the determination of the sound pressure level and the sound power level. The aim was to describe the methods for the determination of the measurement uncertainty generally, in order to be adapted to several products and test methods. It was realised partly by collecting information from manuals, standards and reports from earlier investigations and partly from performing measurements. There are several reasons for measurement uncertainty and they are either of random or systematic character. Random errors arise from unpredictable variations of influence quantities such as variations in temperature or atmospheric air pressure. Systematic errors always appear with the same size and sign in every measurement and are therefore possible to correct to some extent. They may among other things be caused by zero point deviation of the measurement equipment. The measurements were performed on already existing acoustics test-rigs for the determination of the sound pressure level of a high pressure pump respectively the determination of the sound power level of a fuel injector. The two measurements have several uncertainty components in common but also specific characteristics and together they form a good example on how the uncertainty can be determined. To start, all possible influences on the measurement result were listed and divided into four categories of uncertainties due to: environmental influences, the measurement equipment, the measurement set up and the data processing. The quantity to be measured was then described as a function of the result of the measurement and corrections of each possible variable that may have influenced the result. In most cases the correction could be set to zero, but the uncertainty of this setting was used to estimate the total uncertainty of the quantity. With this method it is possible to individually consider each component of the total measurement uncertainty. To know how the total uncertainty is composed makes it easier to improve the measurement method and make it more accurate. The results showed that the uncertainty due to the room and reflections from the wall and the uncertainty due to the mounting of the source contributed the most to the total uncertainty. These are difficult to reduce without modifying the measurement test-rig.

Place, publisher, year, edition, pages
Keyword [en]
Technology, Acoustics, Measurement uncertainty, Airborne noise, Sound, power level-measurement, Sound pressure level-measurement
Keyword [sv]
URN: urn:nbn:se:ltu:diva-46013ISRN: LTU-EX--08/143--SELocal ID: 3a9e1fdd-9387-4e63-85c3-0a9f47c18dcdOAI: diva2:1019321
Subject / course
Student thesis, at least 30 credits
Educational program
Arenaprogrammes (2002-2014)
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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