Force Sensor Characterization Under Sinusoidal Excitations
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.
Realization of Sinusoidal Forces at CEM
This paper describes the procedure implemented at CEM for dynamic force calibration using sinusoidal excitations of force transducers. The method is based on a sinusoidal excitation of force transducers equipped with an additional top mass excited with an electrodynamic shaker system. The acceleration is measured by means of a laser vibrometer.
Laser interferometer and reciprocity calibration of accelerometers using the NIST Super Shaker
The development of the NIST Super Shaker permits calibration of accelerometers by two independent and absolute methods on the same shaker. Minimizing the uncertainty of reciprocity calibrations imposes stringent requirements for distortion and cross-axis motion. Laser interferometer calibrations require very low coupling between the shaker and the interferometer components. The design of the Super Shaker provides for very low distortion and cross-motion with very low mechanical coupling between the shaker and optical components. The shaker is equipped with dual coils and two retractable magnets to provide for reciprocity measurements without attaching a driving shaker. These features enhance the convenience with which the Super Shaker can be used to perform both reciprocity and laser interferometer calibrations. This paper describes the shaker and calibration system and gives a comparison of calibration results from the two methods.