In this paper we present the progress in development of a table-top version of the Kibble balance under the name Planck-Balance 2 (PB2). The PB2 is developed as a collaboration effort between the Technische Universität Ilmenau (TU Ilmenau) and Physikalisch-Technische Bundesanstalt (PTB) aiming for automatized mass calibration of the set of weights in the range from 1 mg to 100 g within the required uncertainties as stated by OIML recommendation R111 for weights of E2 class. We describe the design and the operational performance of the PB2 system in detail, the results of rigorous investigations of the error sources and subsequent improvements made since the beginning of the project in early 2017, the measurement data with the corresponding relative uncertainties and the preliminarily obtained uncertainty budget.
The Planck-Balance is a table-top version of a Kibble balance. In contrast to many other Kibble balances, the coil is moved sinusoidally and an ac rather than a dc signal is generated in the velocity mode. The three-parameter sine fitting algorithm is applied to estimate the amplitudes of the induced voltage and the coil motion, which are used to determine the force factor Bl of the voice coil of the electromagnetic force compensation balance. However, the three-parameter sine fitting algorithm is not robust against some perturbations, e.g. additive Gaussian white noise, quantization error, harmonic distortion, frequency error and time jitter. These effects have influences on the accuracy of the amplitude estimation. Based on numerical simulations and correlation analyses, the effects of these perturbations are determined. By optimizing measurement and data processing approach, the bias and standard deviation of the estimated amplitude can be effectively reduced, and thus the accuracy of the force factor Bl in the velocity mode can be improved.
ZusammenfassungSeit dem 20. Mai 2019 gilt das neue Internationale Einheitensystem SI. Dies stellt eine Zäsur in der Geschichte der Einheiten dar, denn von nun an sind alle 7 Basiseinheiten durch Fundamentalkonstanten definiert. Gerade für die Masse und die daraus abgeleiteten Größen hat das weitreichende Folgen. Das Urkilogramm ist jetzt nur noch ein normales 1 kg-Wägestück. Der Gewinn aber ist enorm. Das Kilogramm lässt sich zukünftig für jeden Massewert darstellen und muss nicht mehr auf das Urkilogramm rückgeführt werden. Da die Kraft bislang über die Masse rückgeführt wurde, öffnen sich aber auch deren Definition neue Wege. In diesem Artikel soll beschrieben werden, wie die prinzipiellen Realisierungen des Kilogramms über die Kibble-Waage und die Röntgenkristalldichtemessungen (XRCD-Methode, oder auf Englisch X-ray-crystal-density method) funktionieren und welche Ideen für die Kraft-Messung bereits umgesetzt wurden.
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