An Introduction to Dynamic Force Metrology

The ability to measure rapidly time-varying quantities is a continued and growing interest in the metrological community, which has been driven, in part, by the need to accurately measure dynamic mechanical quantities (e.g., pressure, force, acceleration). Within the mechanical domain, force indicating instruments are different from most other types of sensors, as the force sensor must also transmit the quantity being measured. Consequently, the force measurement instrument becomes part of the engineering structure or measurement system. While this integration of sensor-system typically does not pose many design or metrological challenges for static or stationary forces, the implications for dynamic measurements are often profound. For example, high-performance force transducers can be statically calibrated with less than 10 parts-per-million uncertainty (k=1); however, the dynamic sensitivity has been shown to deviate by several orders of magnitude from the static sensitivity for certain rates of dynamic forces. We describe some of the physical challenges in making accurate dynamic force measurements, as well as commonly used dynamic force calibration techniques. The introductory dynamic force concepts covered here serve as a foundation for designing engineering systems with the intent of measuring time-varying forces.