Free-mass reciprocity calibration

A simple method for reciprocity calibration of accelerometers and velocity sensors is presented. The useful frequency range is from about 1 Hz to a kilohertz or more and the method is capable of subpercent accuracy. Calibrations with excitation levels from 1 to 300 mm/s² (0.1 mg to 0.03 g) were produced in prototype fixtures. The device to be calibrated and two geophones are used in the calibration fixture. Since the geophones are both reciprocal, a direct test of reciprocity can be done prior to the calibration to evaluate the apparatus. In contrast to standard techniques, the method requires only one relatively inexpensive mechanical setup.