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CHAPTER 2

Why the Levitation Mass Method Is Needed

No dynamic calibration method for force transducers

For static (time-invariant) forces, calibration systems based on deadweights and the like are well established. But no method had been established for calibrating force transducers against forces that vary with time. When a varying force is measured with a force transducer, two major problems arise.

  1. The uncertainty of the measured value cannot be determined properly.
  2. The distortion of the time axis cannot be determined. How much the output lags behind, and distorts, the actual force is unknown.

"A higher resonance frequency is better" has no logical basis

At present, the resonance frequency is practically the only parameter available for evaluating a transducer's dynamic characteristics. It is widely believed that transducers with higher resonance frequencies measure dynamic forces with smaller uncertainty. But this belief has no logical basis. Dynamic calibration methods using known reference varying forces are urgently needed.

The LMM's answer

The LMM provides a reference force based on the definition of force, the inertial force of a mass, with an arbitrary time waveform. It is free from both problems above.

The same problem for small forces

Demand for evaluating small forces in the range of about 1 mN to 1 N is growing in many industrial and research fields. Yet no method had been established for measuring micro-newton-level forces even statically, and most small forces to be generated or measured vary with time. The LMM applies here too (Chapter 7).

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The Levitation Mass Method: precision force measurement by the definition of force | Yusaku Fujii (Gunma University)