Introduction

For many years the National Physical laboratory has been encouraging measurement good practice both through written publications and training courses. Much is made of measurement good practice but how do we define good practice? The guiding principles that NPL use to define measurement good practice are:

The Right Measurements: Measurements should only be made to satisfy agreed and well-specified requirements.

The Right Tools: Measurements should be made using equipment and methods that have been demonstrated to be fit for purpose.

The Right People: Measurement staff should be competent, properly qualified and well informed.

Regular Review: There should be both internal and independent assessment of the technical performance of all measurement facilities and procedures.

Demonstrable Consistency: Measurements made in one location should be consistent with those made elsewhere.

The Right Procedures: Well-defined procedures consistent with national or international standards should be in place for all measurements.

The principles form the basis of NPL's measurement good practice guides of which there are now over 130.

This article will concentrate on NPL's dimensional measurement good practice guides and will highlight the available guides and recent work to update them. There are fourteen guides relating to dimensional measurement and they are listed in Table 1.  The guides are very popular with hundreds of copies being downloaded every month. In November 2014 Fundamental Good Practice in Dimensional Metrology was downloaded 195 times, Callipers and Micrometers 187 times, CMM Measurement strategies 162 times and Dimensional measurement using vision systems 128 times.

Table 1 Dimensional Metrology Good Practice Guides

 

 

How to download the updated dimensional metrology guides   Visit the NPL website at http://www.npl.co.uk/publications/guides/dimensional-good-practice-guides to download your free guides

 

Updating the dimensional guides

 

In 2011 Guide Number 42 CMM verification was updated to reflect the 2009 release of ISO 10360:2 and new Guide Number 130 Co-ordinate measuring machine task specific measurement uncertainties was also produced.

However, around about this time NPL also realised that many of the other dimensional guides first produced in 2001 were in need of updating so a project funded by the UK National Measurement System Programme for Engineering & Flow Metrology was started to update guides 37, 39, 40, 41 and 43 with the aims of removing out of date information, producing the guides in a more modern A5 format and to reflect changes in technology. Over the last year NPL scientists have been working to update these guides and they are now all available on the NPL website.

The updated guides are listed below with a brief indication of the main changes.

The measurement of surface texture using stylus instruments

The guide has been reformatted in the style of more recent guides and the photographs and images improved. References to international standards have been updated as appropriate.  This guide now references the other surface texture guides that relate to optical measurement techniques.

Dimensional measurement using vision systems

The guide has been reformatted in the style of more recent guides and the photographs and images improved. The changes to this guide are of an interim nature with a fuller guide on vision systems planned for the future.

Callipers and micrometers

This good practice guide has been updated to reflect the replacement of British Standards with their ISO equivalent. The main change introduced with the replacement ISO standards is that the new standards are less prescriptive.  Whereas the older British Standards had tables of tolerances for the various metrological characteristics, the replacement ISO standards leave the choice of tolerance to the instrument manufacturer.  The implications of this change are highlighted in the guide. The guide has been reformatted in the style of more recent guides and the photographs and images improved.

CMM measurement strategies

The guide has been reformatted in the style of more recent guides and the photographs and images improved. In addition the guide has been updated to reflect the use of virtual CMM software to design probing strategies and to link to Good Practice Guide No. 130.

CMM probing

The guide has been reformatted in the style of more recent guides and the photographs and images improved. New material has been added particularly sections on microprobing systems, freeform measurement and five-axis scanning probes.

Figure 1 One of the recently updated guides

 

The updated guides are now available on the NPL website and printed copies are available on request. Figure 1 shows the cover of one of the recently updated guides.

Future plans

Having brought the existing guides up-to-date NPL has plans for more guides in the future. The need has been identified for more advanced guides on vision systems and an enhanced probing strategies guide.

Other guides that are planned for the future include

·       Good practice guide on the use of crystalline step heights

·       Good practice guide on error mapping stages

·       Good practice guide on machine tool uncertainty

NPL is also looking at making the guides available in other formats, for instance e-books. NPL measurement good practice guides supplement other forms of learning such as the NPL Dimensional Measurement e-learning course and more traditional classroom based learning provided by NPL's training framework. Details of all these forms of learning can be found on the NPL website.

 

Suggestions for new guides

 

NPL is looking into future requirements for dimensional good practice guidance and training courses and would like your view. To have an influence on future good practice guides, please complete our survey at website: www.surveymonkey.com/s/Dimensional

 

How to tell us about your needs for dimensional metrology guides and training courses   NPL is looking into future requirements for dimensional good practice guidance and training courses and would like your view. To have an influence on future good practice guides, please complete  our survey at website: www.surveymonkey.com/s/Dimensional

 

Obtaining information and advice from NPL

 

Not all good practice can be covered in NPL good practice guides and training courses. If you have a difficult dimensional measurement problem or just need some advice you can contact NPL at E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it..