Improved standard for the calibration of vibration pickups

Abstract

As part of a continuing program on the development of primary vibration standards, an electrodynamic standard was modified so that it is free of transverse motion throughout almost all of its frequency range. The rectilinear sinusoidal motion produced by the standard is achieved by suspending the moving parts of the standard from the frame by tensioned wires. The standard consists of an electrodynamic vibration exciter equipped with a velocity-sensing coil which is calibrated by the reciprocity method. In the vibration-pickup calibration service recently established at the National Bureau of Standards, the standard is used at frequencies from 10 to 2000 cps at accelerations up to 10 g. The errors of the motion applied to the pickups do not exceed 1% up to 900 cps and 2% between 900 and 2000 cps. Government and industrial research laboratories use selected electrodynamic velocity, variable resistance and piezoelectric acceleration vibration pickups calibrated on the standard as secondary vibration standards. If properly used these secondary standards can be used to calibrate other pickups by measuring the ratio of their outputs.