Scale factor determination of spring type gravimeters in the amplitude range of tides by a moving mass device

Abstract

This paper investigates the characteristics and the metrological limits of the calibration of spring type gravimeters by using a cylindrical test mass moved vertically around the gravimeter by a lifting device operated in the Mátyáshegy Observatory. The movement of the 3100 kg iron mass generates a sinusoid-like calibrating signal having a peak-to-peak amplitude of 1102 nm s −2 . The careful determination of the geometrical and physical parameters of the test mass combined with the analytical modeling of its gravitational effect and the related uncertainties provides an accuracy of 3 nm s −2 in absolute sense. The overall accuracy, however, is influenced by several other instrumental and environmental factors which are investigated in detail. The conclusions are based on more than 400 experiments with 5 LCR G instruments. As a unique case a Scintrex CG-5 instrument was also involved in the tests what is probably the very first moving mass calibration of this type of gravimeters.Two processing methods, Max-Min and Full-Fit, based on L2 norm adjustment of the observations were developed and applied to obtain instrumental scale factor and other related parameters.The results show that the observations corrected for the disturbing effects still contain a systematic constituent with amplitude of (10-20) nm s −2 regardless which LCR instrument was calibrated. It resembles the second time derivative of the calibrating signal that may indicate the non-uniform elastic response of the spring sensors to the rate of gravity change. Due to the problems mentioned above the overall dispersion of the resultant random and nonrandom residuals of the calibration observations provided by Full-Fit method are typically 10 nm s −2 . The a posteriori standard deviations of the individual scale factors provide, however, measurement accuracy of 2 nm s −2 .

Newtonian (moving mass) calibration of tilt and gravity meters and the investigation of some factors influencing its accuracy

“…Due to size constraints, only LaCoste and Romberg gravity meters (both G and D types) could be tested at that time. Just recently Koppán et al (2020) have tested successfully Scintrex CG-5 instruments too. It has to be mentioned that ring masses (as perturbing gravitational sources) have also been used for the laboratory determination of the universal gravitational constant G (e.g.…”

“…For G determination, only the mass and geometry of the ring mass have to be known, the value of G can be derived from the exact measurements of the trajectory perturbations of a free falling test mass. Koppán et al (2020) showed that the Mátyáshegy device is excellent for gravimeter testing at real sub microGal (1μGal 10 nm/s 2 ) level since the careful and complex analysis of the accuracy of the reference signal generated by the cylindrical mass provided a maximum uncertainty of ±3 nm/s 2 in absolute sense. This analysis, however, could not be a complete study.…”

“…The off-axis computations (Koppán et al 2020) of the gravitational effect ( g ( g x , g y, g z )) of the cylindrical ring of Mátyáshegy MMC device defined by parameters r 1 160 mm, r 2 385 mm and L 1030 mm (Fig. 6) showed that near to its inner mantle, a significant change of horizontal mass attraction g xy ( g x ) 2 + g y 2 can be observed during the vertical movement of the mass.…”

“…Following the notation of the paper (see Fig. 2a, Koppán et al 2020) the height of the mass is marked by l (0 mm ≤ l ≤ 1300 mm). The height l 0 mm refers to the start position of the lifting process, when the top face of the cylindrical ring is below the sensor.…”

“…When l 0 the cylindrical ring mass rests on the floor and the sensor of either the gravity or the tilt meter is above the upper horizontal plane of the cylinder by about 15 cm (Fig. 2a, Koppán et al 2020). A simple vertical shift can be applied to transform the vertical positions from one system to the other one (Fig.…”