The National Physical Laboratory (NPL) is the UK's National Measurement Institute well known for providing the traceability against which every day metrology is based. One of the tasks undertaken by NPL is the certification of Reference Master Gauges to American Petroleum Institute (API) Specifications, a role they undertake on behalf of the European Association of National Metrology Institutes (EURAMET) for the whole of Europe. API gauges are commonly used in the oil and gas industry.
Until recently the process to certify API gauges has been extremely time consuming and labour intensive. In order to reduce the time required for calibration NPL and Hexagon Metrology undertook a project to look at other methods for the measurement of the majority of features on these taper thread gauges. Engineers from the NPL and Hexagon Metrology's Leitz factory in Germany worked together to investigate how a Coordinate Measuring Machine (CMM) could be utilised. Two key elements were the need for a highly accurate measurement facility and a software platform competent of coping with the necessary calculations.
"The Leitz PMM-C Infinity with a specified maximum permissible error of 0.3 + L/1000 was chosen as the CMM is capable of automatically measuring API gauges to the measurement uncertainties required", explains David Flack, NPL Engineering Measurement. "In addition the software application deemed suitable for the task was QUINDOS, in particular the module for Screw Thread Inspection. The software, Hexagon Metrology's applications team, and trials on NPL's existing Leitz PMM have proven to us that this is the right solution."
In addition NPL is looking to use the Leitz PMM-C Infinity as a platform for measuring artefacts such as ring gauges, plug gauges, end standards and line standards in much the same way as NPL's existing Leitz PMM is used for the calibration of step gauges.