Effect of Nonaxial Motion on Accelerometer Calibration

Abstract

It is usual to monitor harmonic distortion, noise, and hum in the pickup signal during calibration but this is not enough to ensure suitable motion for accurate calibration. This paper describes calibration of all accelerometer on two shakers which were monitored for nonaxial motion. The nonaxial motion was detected by comparing the signals from three small pickups cemented equidistantly around the periphery of the shake table and the signal from the pickup being calibrated which was mounted at the center of the shake table. Each of the four pickups provided the signal for the vertical axis of a Lissajous figure. All of the Lissajous figures had a common horizontal signal which came from the oscillator driving the shaker through a calibrated phase shifter. A special eight channel electronic switch was used to put all of the Lissajous figures on the same CRO. During axial pistonlike motion all of the figures behaved similarly. During nonaxial motion the relative sizes and inclinations differed. The phase shifter provided a means for measuring differences in the phase of the motion at the pickup locations. Valid calibration points fell on a smooth curve. Points taken when the monitoring system showed nonaxial motion for a given shaker at a particular frequency fell off the curve while the calibration point taken at the same frequency with the other shaker which showed good motion fell on the curve.