ASME Measurement Uncertainty Standard

The National Institute of Standards and Technology (NIST) engineers, together with colleagues from industry and other standards organizations, have completed a five-part series of standards designed to evaluate the accuracy and usability of manufacturing measurements.

The American Society of Mechanical Engineers (ASME) recently published the last in the series, B89.7.3.2 – 2007, Guidelines for the Evaluation of Dimensional Measurement Uncertainty. A copy can be obtained for $35.00. Click on the title above to go to its ASME Product Catalog entry.

B89.7.3.2 – 2007 addresses the evaluation of dimensional measurement uncertainty, with an emphasis on simplified methods for the industrial practitioner. Its introductory methods are consistent with the Guide to the Expression of Uncertainty in Measurement (GUM), the nationally and internationally accepted method to quantify measurement uncertainty.

The five-part series describes ways that measurement personnel can communicate, evaluate, and respond to uncertainties in manufactured part measurements. Adopting these standards on the shop floor should enhance manufacturing productivity and minimize the scrapping of acceptable parts, unnecessary rework, and even litigation.

In the past, shop engineers could relax if component parts varied slightly from specification. Parts just had to “fit together.” However, the complexity of many current products requires more advanced measurement capabilities. The ASME standards are needed because measurements often vary each time they are made (even the temperature of the part can change the measurement result by a significant amount).

The B89.7 series also explains dimensional measurement traceability. Traceable measurements demonstrate the connection between the standard international (SI) unit of length (the meter) and the task-specific measurement under consideration; this also requires an uncertainty statement describing the accuracy of the measurement result.

The B89.7 series addresses:

  • the role of measurement uncertainty when accepting or rejecting products based on a measurement result and a product specification;
  • economically efficient methods to overcome differences between two parties in the evaluation of measurement uncertainty;
  • how to determine the economically appropriate decision to accept or to reject a product due to measurement uncertainty; and
  • ways to demonstrate dimensional measurement traceability to the SI unit so that all parties can be sure of the reliability of their measurements.

NIST researchers chaired the ASME B89.7 working groups and contributed to other related development work during the five-years it took to develop the five standards. For information on the ASME B89.7 standards, click on this ASME Product Catalog web page.