Apparatus for Testing Gravimeter Based on Sinusoidal Modulation of Gravitational Signal

The apparatus based on the sinusoidal modulation of gravitational signal has been built to test the gravimeter. The combination of attracted mass is moved up and down by the guide rails with a large load-carrying capacity. The maximum acceleration produced by the apparatus reaches
$220.0~\pm ~0.3$
nm/s2. A feedback control is carried out to modulate the moving distance of the attracted mass with an uncertainty of 0.03 mm. As a result, the acceleration is modulated in a sinusoidal wave with a frequency of 0.83 mHz, which is away from the frequencies of tidal signals and environmental disturbances. The CG6 gravimeter is verified by this apparatus. After considering the effects of the temperature, the atmosphere, the gravitational tide, etc, the uncertainty of the verifying is evaluated to be 0.5 nm/s2. The maximum difference in acceleration between the measured result of the CG6 gravimeter and the theoretical value produced by the apparatus is
$1.2~\pm ~10.9$
nm/s2. It means that they agree well with each other within the error range. The uncertainty is mainly introduced by the random fluctuation of the CG6 gravimeter itself. This work provides a sinusoidal modulation method for verifying the gravimeters, which can greatly reduce the environmental influences, such as the effects of the gravity tide and the time drifting. The modulation frequency of the acceleration produced by the apparatus can be adjusted according to the testing requirement, which is helpful to study the response characteristics of the gravimeter at different frequencies.