National Physical Laboratory

Acoustic emission

Oil Rig Photo NPL offers guidance on acoustic emission measurements and calibration, and carries out measurements for customers on a consultancy basis (for enquiries, please contact Dr Pete Theobald).

An acoustic emission research project is also being conducted:


This project aims to address the need for national measurement standards for acoustic emission. Key components will be:

  • development of a robust traceable source for in-situ calibration, to replace the pencil lead break
  • sensor calibration for both out-of-plane and in-plane displacement sensitivity


Acoustic emission (AE) measurement is widely used in industry to monitor the condition of safety-critical and production-critical systems such as pressure vessels, engines and high-speed machinery. It can prevent the need for unnecessary and expensive early shut down of plant, as well as providing the means to minimise expensive, and often dangerous, failures. Recently, there has been more interest in the use of AE as an in-service condition monitor and as an on-line process-monitoring technique. Examples of its use cover a wide spectrum, from monitoring of large pressure vessels, storage tanks, and large structures such as bridges and aircraft structures, to studying tool wear and composition of liquids.


Acoustic Emission Measurement Equipment  Acoustic emission measurement is potentially a very important technology for the future, with the recent increase in computer processing capability providing the opportunity for more sophisticated methods of data analysis. One factor hindering the greater use of AE technology is the lack of traceability. This is particularly important for safety critical and highly regulated industries, such as aerospace and off-shore industries. In discussions, representatives of these industries in the UK cite this lack of traceability as a major obstacle in implementation and adoption of these valuable techniques.

Under the 2004-2007 Acoustical Metrology Programme considerable progress has been made in key areas of concern to industry. One of the major issues is the requirement for a more robust traceable reference source for in-situ calibration of AE measurement systems, to replace the pencil lead break and its associated problems of repeatability and traceability. Full characterisation of sensors in terms of in-plane and out-of-plane displacement sensitivities is also vital if informed decisions on transducer selection are to be made. This programme will build on the current work, collaborating with industry to ensure that the developed reference source is suitable for use in the field, and that calibration services meet their requirements.

Last Updated: 26 Apr 2012
Created: 29 May 2007


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