Accelerometer Calibration Technique

A technique has been developed for the dynamic calibration of accelerometers or other vibration measuring instruments. It is believed that the technique is more convenient than the reciprocity method for making rapid calibrations over a fairly large frequency range. For each calibration frequency the accelerometer is attached to a free-free bar driven electromagnetically at a known sinusoidal amplitude. The accelerometer output is compared in magnitude and phase with the amplitude of the bar. This is done by means of strain gauges on the bar which are calibrated periodically by direct optical measurement of bar amplitude. The importance of various design factors is discussed and also the accuracy of the technique with relation to amplitude and frequency. The error in the phase measurements is about 2 degrees and the double amplitude can be measured to about 0.003 mm. The error in measuring a 200-g accelerometer at 1000 c.p.s. is about 3 percent.