Kibble Balance Resistance Segmentation for Mass Measurement
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Solution Overview
Problem
Kibble scales face challenges in calibration and measurement uncertainty due to their design, which is not traceable to natural constants, and struggle to accurately determine mass across a wide range of weights, especially with lower masses, due to difficulties in determining the geometric factor and relative measurement uncertainty increasing with smaller masses.
Innovation Solution
The kibble scale employs a resistance element with multiple partial resistance elements and adjustable coil configurations to compensate for weight forces electromagnetically, allowing for precise determination of current strength and voltage drops across the resistance element, enabling accurate mass measurement across a range from 1 mg to 1 kg with reduced measurement uncertainty.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single resistance element with fixed resistance is used, then the device complexity is reduced, but the measurement precision across different mass ranges deteriorates due to increasing relative measurement uncertainty with smaller masses
Solution Approach 1:
The resistance element is divided into multiple partial resistance elements (first, second, third partial resistance elements) that can be selectively connected in different circuit arrangements. This segmentation allows the total resistance to be adjusted according to the expected mass range, optimizing the voltage drop across the resistance element for each measurement range and reducing relative measurement uncertainty across the entire 1 mg to 1 kg range.
2Measurement precision
If the geometric factor B*L is determined metrologically, then the measurement precision improves, but the device complexity and difficulty of detection increase
Solution Approach 1:
The kibble balance operates in a feedback-controlled manner where the current I K is regulated to compensate for the weight force F G. The voltage drop U across the resistance element is measured and used to determine the current, while the induced voltage U ind in the coil during dynamic operation provides additional measurement data. This feedback system allows the geometric factor to be determined through electrical measurements rather than direct geometric measurement, reducing the difficulty of detection.
Solution Approach 2:
Instead of determining the geometric factor B*L through direct mechanical or geometric measurement of the coil and magnetic field, the patent uses electrical measurements (voltage drop U and induced voltage U ind) to indirectly determine the product B*L. This substitution of mechanical measurement with electrical measurement reduces the difficulty of detection and improves measurement precision.
3Measurement precision
If multiple partial resistance elements are used with different circuit arrangements, then the measurement precision across mass ranges improves, but the device complexity increases
Solution Approach 1:
The resistance element configuration is made dynamic and adjustable rather than fixed. The switching arrangement allows selective connection of partial resistance elements based on the expected mass of the weight being measured. This dynamic reconfiguration optimizes the voltage drop for each mass range, maintaining high measurement precision across the entire range from 1 mg to 1 kg while managing device complexity through controlled adjustability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution allows for precise mass determination with a maximum relative measurement uncertainty of 10^-3 or less across the entire 1 mg to 1 kg range, maintaining consistent measurement accuracy and reducing the need for frequent voltmeter range switching, while using a compact permanent magnet and varying lever ratios to achieve precise compensation.
Implementation Method 1
when the coil is energized with a current I K , a weight force F G exerted on the load receptor by the weighing piece in static operating mode is caused by an electromagnetic force acting on the coil force F em can be compensated
Implementation Method 2
determine an in voltage U ind induced in the coil when the coil is moved through the magnetic field at a speed v in dynamic operating mode
Data Source
Figure 1
AI summary
The invention relates to a Kibble balance (2) that can be operated in a static operating mode and a dynamic operating mode, comprising (a) a load cell (8) for receiving a load (10), (b) a currentable coil (4), (c) a permanent magnet (6) that generates a magnetic field, and (d) a resistance element (24), (e) wherein the currentable coil (4) is mounted in the magnetic field such that by energizing the coil (4) with a current IK, a weight force FG exerted by the load (10) on the load cell (8) in the static operating mode can be compensated by an electromagnetic force FE acting on the coil (4), and (f) wherein the Kibble balance (2) is configured (i) to determine a voltage drop U across the resistance element (24) when the coil (4) is energized with the current IK in the static operating mode, and (ii) to determine a voltage Uind induced in the coil (4),when the coil is moved through the magnetic field at a speed v in dynamic operating mode. According to the invention, the resistance element (24) has at least two partial resistance elements, wherein the at least two partial resistance elements can be placed in at least a first switching arrangement and in a second switching arrangement, wherein a resulting total resistance of the resistance element (24) in the first switching arrangement differs from the resulting total resistance of the resistance element (24) in the second switching arrangement.