The Frankfurt calibration system for relative gravimeters

Artificial accelerations are used for the absolute calibration of relative gravimeters. Such accelerations are generated by the Frankfurt calibration system. The system consists of three stepper-motor-driven spindle blocks which can be mounted on any arbitrary body: here in the experiment a platform where spring gravimeters can be placed. The vertical motions of stepper-motor-driven spindle blocks are controlled by glass gauges. In a digital feedback loop, imperfections of the screw can be compensated. The driving functions for the stepper motors are sinusoidal waves with periods between 200s and 2400s. With the stroke of the system (+/-10 mm) artificial accelerations up to +/-1000.10(-8) m.s(-2) can be generated. During the experiment twelve gravimeters were investigated. The calibration factors as well as the frequency transfer functions of the instruments were determined with accuracies of better than 10(-3). The results coincide well with the calibration factors derived from the gravity calibration line in Sevres for the same instruments.