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Torque travelling standard shows excellent stability in key comparison

12.09.2006

The first international No matching tab handler could be found for link handler key record:tt_news:1454. in the field of torque piloted by PTB was completed in July 2006. Presently, the results are being assessed and the final report is being prepared. Already now, an outstanding reproducibility in the order of 10-6 can be reported for one of the travelling standards.

The CIPM key comparison CCM.T-K1 up to 1 kN·m that started in May 2005 and was completed in July 2006 serves to ensure the metrological properties of torque standard machines, which have been set up in different regions of the world over the past decade, with smallest relative measurement uncertainties of a few 10-5. PTB's Working Group "Realization of Torque" is the pilot laboratory of this comparison and had to ensure the availability of travelling standards that are solid enough for their properties to remain fairly stable, even after a longer transport to far-away countries (e.g. Japan, Korea, Mexico, Brasil).

Before the start of this comparison, investigations on the two transducers used - a cylinder-shaped TT1 transducer and a TB2 transducer in flange form - had already been carried out, and it had turned out that the TB2 transducer, due to its sealed design, showed a significantly lower reaction to changing environmental conditions (especially air humidity) than the TT1 transducer; the TB2's overall stability was also excellent. The expectations with regard to the comparison measurement were therefore extremely high.

At the pilot laboratory, the transducers underwent a start measurement, as well as a measurement each time they returned from one of the participants. Thereby, a total of approx. 5000 individual values per transducer were recorded at the pilot laboratory; their assessment showed an impressive stability. Figure 1 shows the relative deviations of the individual characteristic values determined at each measurement for the TB2 transducer from their average value. The uncertainty bars are virtually in agreement with the expanded measurement uncertainty of the torque standard machine (here 2·10-5), i.e. the mounting position, for instance, of the transducer does not play a significant role. It must be pointed out that the measured deviations lie already in the order of the resolution and stability of the carrier-frequency amplifier used. Due to the higher sensitivity of the TT1 transducer to environmental influences, the results are in this case not quite as good. An uncorrected maximum deviation of approx. 1·10-5 is achieved; the average value of the deviations is, however, significantly smaller. This is, however, still a result good enough to build a solid basis for the assessment of the comparison.

Relative deviations of the measured values from their average value, and corresponding expanded measurement uncertainties for measurements with the TB2 transducer at the pilot laboratory over a period of one year.

Figure 1: Relative deviations of the measured values from their average value, and corresponding expanded measurement uncertainties for measurements with the TB2 transducer at the pilot laboratory over a period of one year.

Ansprechpartner:

Dirk Röske, FB 1.2, AG 1.22, e-mail: dirk.roeske@ptb.de