Designing Model and Optimization of the Permanent Magnet for Joule Balance NIM-2

The design of the permanent magnet system for the new Quantum Electro-Mechanical Metrology Suite (QEMMS) is described. The QEMMS, developed at the National Institute of Standards and Technology (NIST), consists of a Kibble balance, a programmable Josephson voltage standard, and a quantum Hall resistance standard. It will be used to measure masses up to 100 g with relative uncertainties below 2 × 10 −8 . The magnet system is based on the design of the NIST-4 magnet system with significant changes to adopt to a smaller Kibble balance and to overcome known practical limitations. Analytical models are provided to describe the coil-current effect and model the forces required to split the magnet in two parts to install the coil. Both models are compared to simulation results obtained with finite element analysis and measurement results. Other aspects, such as the coil design and flatness of Bl profile are considered.

Section: Profile Of the Magnetic Fieldmentioning

confidence: 99%

Magnet System for the Quantum Electromechanical Metrology Suite

Marangoni¹,

Haddad²,

Seifert³

et al. 2020

“…The air gap is always centered around the same coil radius r c = 150 mm. As shown in [11], the magnetic flux density in the air gap, B r is approximately determined by…”

Section: Profile Flatness Dependence On the Fringe Fieldmentioning

confidence: 99%

“…At present, all ongoing Kibble balance experiments in the world have chosen permanent magnetic circuits to generate the necessary field required for the measurement [5]- [15]. A typical symmetrical design, which originated at the International Bureau of Weights and Measures (BIPM) [10], and has since been chosen widely by researchers at National Metrology Institutes (NMIs) [7], [11], [13], [15], is shown in Fig. 1.…”

Section: Introductionmentioning

confidence: 99%

A Simple Improvement for Permanent Magnet Systems for Kibble Balances: More Flat Field at Almost No Cost

Schlamminger

Wang

2020

Self Cite

Permanent magnets together with yokes to concentrate the magnetic flux into a cylindrical airgap are widely employed in Kibble balances. These experiments require a uniform magnetic flux density along a vertical path, typically a substantial fraction of the length of the air-gap. Fringe fields that are present at both ends of the air-gap limit the region where the flux density does not change more than a certain relative fraction (here: 5 × 10 −4 ) of the flux density in the center of the magnet system. By simply adding an iron ring with a rectangular cross-section to the inner yoke at each end of the air gap, the effects of the fringe fields can be counteracted, and, hence, the length of the region, where the flux density remains within a given tolerance band is increased. Compared to the alternative, employing a taller magnet, the proposed method yields a magnet system with an extended region of a uniform field without significantly increasing the mass of the magnet system. Potential applications include compact and table-top Kibble balances. We investigate possible adverse effects on the performance of the magnet system caused by the additional rings: magnetic field strength, coil-current effect, and a dependence of the radial field on the radial position in the field. No substantial disadvantage was found. Instead, the method presented here outperformed previously suggested methods to improve the radial dependence of the radial field, e.g., shorter outer yoke. In summary, adding rings to the inner yoke improves the uniformity of the field without a detrimental effect to function, cost, and form factor of the magnet system.

“…Nowadays, the yokebased permanent magnet system has been widely accepted and is a dominant component in most Kibble balances. Among many different magnet realizations, the BIPM-type design is used predominantly [5], [9], [11], [18]- [20]. The advantages of using a permanent magnet system include a high efficiency for generating a strong and uniform magnetic field, good robustness for long-term operation, and low maintenance cost.…”

Section: Introductionmentioning

confidence: 99%

Magnetic Uncertainties for Compact Kibble Balances: An Investigation

Schlamminger

2022

Self Cite

The Kibble balance has become one of the major instruments for realizing the mass unit, the kilogram, in the revised international system of units (SI). Researchers at about a dozen national metrology institutes are actively working with Kibble balances that are capable of weighing masses with nominal values from 10 g to 1 kg. In the future, the design of smaller Kibble balances will play a more significant role. Smaller Kibble balances require smaller magnet systems, and here we investigate the scaling of systematic uncertainties with the size of the magnet system. We describe the size dependence of three magnetic effects: the coil-inductance effect, the yoke nonlinear effect, and the thermal effect. The analysis shows that the relative systematic effects become increasingly larger with smaller sizes. For small magnets the thermal effects become dominant and, hence, a good thermal design is imperative.