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Multi-wave Standards – a Breakthrough in Form Measurement

Cylindrical bodies carrying a special wave pattern on their surface establish the new state of the art for transfer standards for form measurements. The signal characteristics of these so-called multiwave standards make it possible to calibrate the signal transmission chain of form-measuring instruments in a highly stable manner.

The partial view of the multi-wave standard (diameter 80 mm) shows the lateral wave pattern. The standard is turning underneath the mechanically touching sphere, the horizontal movement of which produces the measurement signal.

Picture below:
In the spectrum of a multiwave standard, the characteristic lines correspond to the embodied sinusoidal waves.

The sensitivity calibration of form-measuring instruments is in general performed by doing roundness measurements for standards with defined deviations from the circular cylindrical form. Flick standards (cylinders with a flat) have so far been used for this purpose. However, their signal characteristics are typically small-band, and data evaluation is based on only very few data points of the profile.

In contrast to this, a new measurement procedure developed by PTB provides information about a broad spectral band. Moreover, this procedure is based on all data points of the profile. Prerequisite is the multi-wave standard, a cylinder with a well-defined superposition of sinusoidal form deviations of different amplitudes and wavelengths.

The spatial signal of the multi-wave standard corresponds to a line spectrum. The wavelengths have been selected according to ISO Standards (5, 15, 50, 150, and 500 upr). The measured form profile is evaluated by Fourier analysis. This is made possible by the purely harmonic signal of the multi-wave standards. The form-measuring instrument is calibrated by comparing the measured amplitude heights of the spectral lines with the calibrated line spectrum. Small local disturbances hardly influence the calibration result, because the amplitude spectrum is integrally evaluated by the analysis procedure.

First practical tests of multi-wave standards have been completed successfully. Comparison measurements with DKD laboratories concerned with form measurements showed agreement within 30 nm in the amplitude height for form deviations of 20 mm as calibrated by PTB. These results prove the progress achieved in comparison with the methods currently applied. Drafts of new standards and guidelines for form measurements have already been influenced by this development.

In summary, multi-wave standards provide a solid basis for the traceability of form measurements. Therefore, they are of great significance for users in calibration laboratories and for industrial quality assurance.

Contact at PTB:

Phone: +49-531-592-0