The PTB at the Sinsheim Control

In the past years, the Sinsheim Control has developed into one of the most important European specialist fairs for quality assurance. Organized for the first time in 1987 as a regional fair, it has constantly expanded as regards the number of both visitors and exhibitors and has since then become a central platform for questions of quality control. High-quality offers on the part of the exhibiting firms on the one side and qualified, specialized fairgoers on the other, combined with growing popularity of this fair in the quality sector, also on the international level, induced the PTB last year to participate. Number, duration and intensity of the technical discussions held there, chiefly about problems concerning the Deutscher Kalibrierdienst (DKD, German Calibration Service), have been the starting point for the PTB's decision to take part also this year.

At the PTB's stand, members of its staff will provide information about the organization and tasks of PTB and DKD, answer questions concerning accreditations, the mutual recognition of calibrations, tests and certifications etc., and be available for discussions about technical problems involved in the calibration of measuring equipment.

As an example of latest results achieved in its research work, the PTB will present a new method for measuring the differences between gauge blocks.

Gauge blocks are the most simple and most accurate material measures of length and are therefore an essential component of industrial metrology. The criteria of quality management, which have been generally accepted to an ever increasing extent in the past years, require that the large number of gauge blocks used must be calibrated at regular intervals. Two methods are applied for this purpose:

1. Calibration by interferometry allows the gauge block to be directly linked up with wavelength standards recommended on the international level. This method is, however, rather expensive and is therefore used only for the most precise gauge block standards.
2. The majority of the gauge blocks are calibrated by mechanical difference measurement. The difference between the length of a gauge block standard and that of a test object is measured by means of two inductive gauging heads of the mechanical type. This difference is usually smaller than 1 µm.

This method is simple, reliable and allows uncertainties of measurement to be achieved which, under favourable conditions, are only slightly higher than the standards' uncertainties. As a large number of standards must be held in readiness for the nominal lengths commonly used, high costs arise for their re-calibration.

To eliminate this drawback, a method has been developed which allows length differences of up to 10 mm to be measured. For this purpose, the upper inductive gauging head of a gauge block measuring device used in mechanical difference measurements has been replaced by an interference-optical head of high linearity and resolution. The PTB's investigations show that the number of standards required to ensure traceability to the unit of length can be substantially reduced with this new method and that the uncertainties of measurement of 0,05 µm + 0,5 · 10^-6 ·l can be reached also in future when appropriate environmental conditions are complied with.

The new method stands out by a considerable reduction of the calibration costs for standards and increased flexibility in the measurement of uncustomary nominal lengths.