Our calibration services are for the highest accuracy grades of length bars and long gauge blocks. Length bars and long gauge blocks in both metric (up to 1270 mm) and inch (up to 50 inch) sizes can be measured. The measurements are made in environmentally-controlled laboratories using purpose-built equipment designed by NPL. Three services are offered:
Length bars and long gauge blocks are among the most commonly used standards for maintaining traceability in engineering. Before use, all length bars and long gauge blocks must themselves be calibrated according to various specification standards such as BS 1790, BS 5317 and ISO 3650. Length bars and long gauge blocks must also be re-calibrated periodically to maintain their accuracy. In order to satisfy these requirements, NPL offers comprehensive calibration services for length bars and long gauge blocks from 25 mm to 1270 mm in length. These services are accredited by UKAS and internationally recognised under the CIPM Mutual Recognition Arrangement. These popular services normally require prior booking but may be available on-demand, depending on loading.
Our calibration service offers the following features:
Gauge block and length bar types we calibrate:
Measurement uncertainty
Measurement by interferometric comparison:
Measurement by absolute interferometry:
Measurement of thermal expansion coefficient:
Measurement uncertainties are quoted at 95 % coverage probability where L is the length of the gauge in mm and Q(a, bL) is the root sum square of a and bL.
NPL's length bar and long gauge block services are covered by the CIPM MRA and are UKAS-accredited.
More information on the care and use of gauge blocks is available in a dedicated Good Practice Guide
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