Electrodynamic reciprocity method for vibration standards

Abstract

In a previous paper, a reciprocity calibration formula different from the Levy–Bouche’s is derived [L.-F. Ge, Proceedings of the XIII IMEKO World Congress, 2606–2610 (1994)]; the latter has been regarded as a standard method [ISO 5347-0, 1987; ISO/DIS 5347-20, 1990]. The new formula is S=(RT/jω)1/2 (V/ms−2), where T is the mean of the transfer admittance ratio, Tn=Mn/(Yn−Yo) and R is the voltage ratio for the typical three-transducer-two-experiment procedure, in which an electrodynamic transducer serves as reciprocal one. This method is suited to the low- and mid-frequency ranges, and most accurate at 100–1000 Hz. This paper reveals that a coefficient of variation, i.e., ratio of standard deviation of Tn to its mean value, can be viewed as a reciprocity index of such an electrodynamic calibration system including two transducers and a solid mass medium. An index smaller than 0.5% indicates that the system is better reciprocal, and can be calibrated more accurately. At frequencies higher than about 3000 Hz, nonlinear problems, such as stress wave effect and resonance, become pronounced, and should be considered; a better way would be to apply other more available methods, such as the laser interferometry and piezoelectric reciprocity method.