Calibration of gauge blocks at The National Laboratory

Purpose

The National Laboratories are responsible for maintaining the national reference standards for each measurement quantity and spreading metrological competence and traceability to industry and society at large. The national reference standards are the highest level of traceability in Sweden.

A calibration performed at a National Laboratory fulfils all typical traceability and accreditation requirements that commonly exist in industry and society at large. 

Method

Gauge blocks are the universal standards that makes it possible to transfer the definition of the metre to a solid standard. We offer calibration of gauge blocks from 0,1 mm -1000 mm, made by steel, tungsten carbide or ceramic materials within three different uncertainty levels. Interferometrical calibration of gauge blocks is our most accurate measuring method, and a direct application of the definition of the central length of a gauge block. The gauge block is wrung to the plane surface of an auxiliary plate and the central length is defined as the perpendicular distance between the surface of the platen and the middle point of the gauge block's top surface. To determine this distance we are using several, different wave lengths of light.

Interferometrical measurements (method “A”) are used when the best accuracy is needed. One typical application is gauge blocks used as standards for mechanical calibration of other gauge blocks. Interferometrical calibration requires very high-quality gauge blocks. The gauge blocks should fulfil grade K according to EN ISO 3650 and have burr free measuring faces.

When the accuracy needed is slightly lower, the gauge block can be measured by mechanical comparison. This method is based on comparison between a standard gauge block and a customer gauge block. We offer two accuracy levels, methods B and C. We are able to calibrate the central length and the length at the four corners for all metric standard lengths from 0,1- 500 mm. That makes it possible to determine the variation in length. For gauge blocks above 500 mm to 1000 mm only the central length is measured.

Method B is intended mainly for gauge blocks used in a laboratory, where high accuracy is needed. Mostly gauge blocks that fulfil Grade 0 or 1, according to EN ISO 3650.  

Method C is mostly used for gauge blocks used in an industrial environment, for example to calibrate handheld measuring tools. Mostly gauge blocks that fulfil Grade 1 or 2, according to EN ISO 3650.

Deliveries

The calibration results are reported in a digital calibration certificate in Swedish or English which states that the calibration was performed at a National Laboratory.