Abstract
The aim in the current work is the development of a method to characterize force sensors under sinusoidal excitations using a primary standard as the source of traceability. During this work the influence factors have been studied and a method to minimise their contributions, as well as the corrections to be performed under dynamic conditions have been established. These results will allow the realization of an adequate characterization of force sensors under sinusoidal excitations, which will be essential for its further proper use under dynamic conditions. The traceability of the sensor characterization is based in the direct definition of force as mass multiplied by acceleration. To do so, the sensor is loaded with different calibrated loads and is maintained under different sinusoidal accelerations by means of a vibration shaker system that is able to generate accelerations up to 100 m/s2 with frequencies from 5 Hz up to 2400 Hz. The acceleration is measured by means of a laser vibrometer with traceability to the units of time and length. A multiple channel data acquisition system is also required to simultaneously acquire the electrical output signals of the involved instrument in real time.
Highlights
Static calibration of force sensors has a well-established procedure, which is fully described in ISO 376 [1], many applications of force transducers are in dynamic conditions
Examples are impact testing for security in vehicles, modal testing for structures and materials to check their seismic behavior or robotized systems used in many applications. As it will be described through this article, important effects and corrections have to be taken into consideration for the proper use of a force sensor under dynamic conditions; as a consequence, it is clear that an adequate dynamic characterization of the force sensor is essential
In order to address these needs, some National Metrology Institutes are currently working in the development of traceable methods to characterise force sensors under dynamic conditions, which are being realized by means of shock and sinusoidal forces
Summary
Static calibration of force sensors has a well-established procedure, which is fully described in ISO 376 [1], many applications of force transducers are in dynamic conditions. Examples are impact testing for security in vehicles, modal testing for structures and materials to check their seismic behavior or robotized systems used in many applications As it will be described through this article, important effects and corrections have to be taken into consideration for the proper use of a force sensor under dynamic conditions; as a consequence, it is clear that an adequate dynamic characterization of the force sensor is essential. Being a fully dynamic measurement it requires a multichannel data acquisition system in real time It will acquire electrical output signals from the laser vibrometer, sensor under calibration, and other auxiliary accelerometers. In calibrations under dynamic conditions the sensitivity uncertainty will be larger than the sensitivity uncertainty under static conditions This difference is such that any possible dependency on the force can be considered negligible if compared with the standard uncertainty, which can be obtained in the determination of the dynamic sensitivity. This work will focus on the dependency of the sensitivity on the excitation frequency and the possible dependency on the force will be considered negligible
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