Norbert Rogge

We compared results from three different tabletop Kibble balances operated at TU Ilmenau, Physikalisch-Technische Bundesanstalt, and National Institute of Standards and Technology using two circulated mass sets. Each set contained five International Organization of Legal Metrology (OIML) R 111 nominal values from 1 mg to 10 g and one deliberately chosen non-OIML value of 6.62 607 015 g. The manufacturers calibrated the sets independently against OIML E 1 target specifications. Data exchange used digital calibration certificates, and all calibration and participant results were withheld until the final unblinding and evaluation. For each mass, we calculated an inverse-variance weighted reference value from the three Kibble balance results and compared it with the manufacturer calibration value. The weighted reference values differed from the manufacturer values by at most 15 μ g. For the gram-level masses, the corresponding relative deviations were below 2.3 × 10 − 6 . Eleven of the 12 cases satisfied | E n | ⩽ 1 . The remaining case had E n = 1.3 . The individual Kibble balance results were less uniform: reported expanded uncertainties ranged from about 0.4 μ g to 160 μ g and differed by up to approximately a factor of 230 for the same nominal mass. These results indicate compatibility at the level of the weighted reference values, while the individual uncertainty levels and measurement performance are not uniform across implementations.

This work showcases the novel possibilities that the use of range-resolved interferometry (RRI) can provide to high-precision force measurement systems based on the Kibble principle. The RRI technique, using sinusoidal laser frequency modulation of diode lasers, enables the simultaneous readout of multiple interferometric phase signals that differ in their optical path differences, enabling the direct measurement of differential motion signals along a single optical beam. The conceptual optical and mechanical system design along with the methodology for data synchronization for the velocity mode measurements in a table-top photon momentum setup is described. Velocity measurements of oscillatory motions with frequencies between 0.1 Hz and 150 Hz and with deflections amplitudes of up to 50 µm are obtained at sub-nm resolution. Metrologically well-characterized cuboid-shaped glass blocks are used as partial reflectors along the measurement axis to obtain multiple interference signals. This optical configuration, which uses only a single straight measuring beam can significantly minimize errors due to angular misalignment and tilt and therefore shows a new route to ultimately lower geometric uncertainties in Kibble-based setups.

This article presents the development of a novel, active measuring head for coordinate measuring machines that is capable of measuring forces and torques in six degrees of freedom (6 DoF) during tactile sensing. It uses a so-called flotor as carrier of the stylus, which is kept in levitation by six electromagnetic voice coil actuators (VCA) in an hexapod-like arrangement. These VCAs function simultaneously as actuators and as force sensors, which are calibrated in situ according to the Kibble balance principle. Additionally, a position and orientation measurement system is integrated, consisting of three two-dimensional position sensors that can detect the position and orientation of the flotor in 6 DoF. The article describes the basic functionality as well as the most important technical functional elements and key design features. These features aim to optimise the metrological properties of probing force and position measurement in order to achieve the lowest possible measurement uncertainty. Furthermore, the structure of the peripheral electronics system for the controlling of the coordinate measuring head is described. So far, the conceptual and structural design has been implemented, two prototypes have been manufactured and put into operation. At the time of publication, initial metrological investigations are being carried out.

The presented paper describes the measurement of anelastic effects of electric discharge machined titanium load cells. The load cells were manufactured with a new design, which allows an interferometric measurement of the anelastic effects with a good signal to noise ratio. FEM simulations are used to calculate the arising stresses. An improved data evaluation reduces the influence of drift effects, which allows a better comparison of load cell specimens with different materials and hinge thicknesses. The observed effects, including their sensitivity towards material thickness and load, are compared to the effects of a common aluminum alloy.

The Planck-Balance is a compact Kibble balance, designed for the realization of the unit of mass at values much smaller than 1 kg across multiple orders of magnitude. Recent advancements enable the Planck-Balance at PTB to measure mass with uncertainties equivalent to calibration accuracy classes E1 (up to 5 g), E2 (up to 50 g), and F1 (up to 100 g), while operating in air. Type B uncertainties limit the relative combined standard uncertainty for a mass of 100 g to the minimum achievable value of 4.5 · 1E−7. A measurement campaign was conducted using six mass standards (1 mg, 10 mg, 100 mg, 1 g, 10 g, and 100 g), yielding results consistent with the values specified in their E1 calibration certificates. The presented results demonstrate the feasibility of metrologically traceable small mass measurements without reliance on mass standards. Unique design features of the Planck-Balance will be discussed, including a rigidly mounted coil that minimizes geometrical alignment requirements, and an oscillatory velocity mode that achieves a high signal-to-noise ratio, even with a movement range of less than 0.2 mm. This approach could offer an alternative to calibration and dissemination using mass comparators.

The adaptation of developed metrology-grade ac current source (MCS) to the velocity mode of measurements of the Planck-Balance 2 as a means for generating ac mechanical oscillations is presented. The universality in operating with the MCS unit especially practical for the Planck-Balance setup for frequencies of 0.1 Hz–20 Hz (including but not limited to the negligence of a broader range of 0.01 Hz up to several hundred Hz) and for amplitudes of up to 10 mA with 16 (offset with 14)-bit effective resolution is demonstrated. MCS allows generating complex ac waveform signals as waveform synthesizers by adding to the original signal an extra five independent harmonic components, each of which with an adjustable resolution of 10 ns for phase and 16-bit for amplitude. Additionally, the MCS is supported by an external clock at 10 MHz frequency which serves also as a common reference time base for the comparison between the direct output signal of MCS, or of the induced voltage in the coil of the Planck-Balance resulting due to the applied current by MCS, with the ac quantum voltage standard at the required accuracy levels.

This article presents a fiber interferometric sensor (FIS) for measuring the velocity amplitude of an oscillatory vibrating object, with a focus on velocity mode measurement in applications using the Kibble balance principle. The sensor uses the range-resolved interferometry method to measure the displacement of the moving object and employs a multi-harmonic sine-fit algorithm to estimate the displacement amplitude and frequency, thereby determining the velocity amplitude. This article provides a comprehensive explanation of the experimental setup and the measurement techniques employed, as well as a detailed analysis of the uncertainty budget, with the performance validation of the FIS benchmarked against a commercial interferometer within a Kibble balance setup. The velocity amplitude of a coil of the Kibble balance, oscillating with an approx. amplitude of 20 μm and a frequency of 0.25 Hz, was measured using the sensor and found to be 31.282 31 μm s⁻¹ with a relative deviation of −1.9 ppm compared to a commercial interferometer. The high performance of the FIS, especially with regard to non-linearity errors, and the small size of the measuring head enable universality of integration into a wide variety of measurement systems, also including the use as general-purpose vibration and displacement sensor.

The paper presents crucial design considerations for the actuators in a table-top Kibble balance, especially its influence on the uncertainty contribution by the voltage measurements. The resulting contribution is exemplary shown for the PB2 version of the Planck-Balance and constraints are discussed that limit the possibilities to optimize the geometric factor of the measurement actuator.

Design and operational performance of table-top measurement apparatus is presented towards direct Planck constant traceable high accuracy and high precision small forces and optical power measurements within the SI unit system. Electromagnetic force compensation weighing balances, highly reflective mirrors and high-energy pulsed laser unit (static average power 20 W) are tailored together with a specially developed opto-electro-mechanical measurement infrastructure for cross-mapping the scale-systems of two different precision small force measurement methods. One of these methods obtains the force measurements by a state-of-the-art classical kinematic system employing the partial use of Kibble balance principle in the range of 10 nN to 4000 nN to be compared with forces generated due to quantum-mechanical effect namely the transfer of the momentum of photons from a macroscopic object. Detailed overview of the adapted measurement methodology, the static and the limits of dynamic measurement, the metrological traceability routes of the measurement parameters, quantities and their measurement uncertainties, parametric estimation of up (down)-scaling perspectives of the measurements are presented with respect to the state-of-the-art measurement principles and standard procedures within the newly redefined International System of Units (SI).

Article Frontmatter was published on December 1, 2021 in the journal tm - Technisches Messen (volume 88, issue 12).