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Dimensional measurements

Angle standards and instruments

Providing accurate angular measurements

NPL offers a calibration service for several types of angle standards, including autocollimators, polygons, angle gauges and indexing tables. Measurements are based on either the division of the circle by precision indexing or by means of a precision sine-bar. 

Calibration of combination angle gauges

NPL provides a UKAS accredited calibration service (laboratory No. 0478) for the calibration of combination angle gauges for compliance with NPL Specifications of Accuracy MOY/SCMI/18.  Angles are determined by means of precision indexing and the NPL small angle generator. Measurements of flatness, squareness and parallelism of the faces are also carried out.

Calibration of autocollimators

Autocollimators are calibrated using the NPL-designed small angle generator. Visual, photoelectric and digital autocollimators are calibrated over both their major and sub-ranges and can be rotated to achieve measurements over both vertical and horizontal axes.

Calibration of indexing tables

Generation of angle by indexing tables is achieved by the meshing of two similar sets of serrations. Calibration of such tables is carried out by mounting the test table on top of one of the NPL indexing tables and using a mirror-autocollimator system to compare angles generated by the table under test with similar angles generated by the NPL table. This service is UKAS accredited calibration service (laboratory No. 0478).

Calibration of polygons

Glass and steel reference and calibration grade polygons are accepted for calibration. Polygons are examined for compliance with the NPL Specifications of Accuracy MOY/SCMI/83 and MOY/SCMI/87. Measured errors of the exterior angles of the reflecting faces are determined together with flatness and squareness. 

The accredited capabilities for these services are listed under the Service Reference code LD08 and found in the calibration and testing schedule issued by UKAS (laboratory No. 0478). For further details please see https://www.npl.co.uk/quality.

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