Permalink : http://hdl.handle.net/2115/84679

JaLCDOI : 10.14943/gbhu.85.11

We calibrated five LaCoste & Romberg relative gravimeters (serial numbers: G031, G534, G605, G680 and G791) belonging to Kyoto and Hokkaido Universities in December 2021, in order to standardize readout sensitivity of these gravimeters. The readout sensitivity can be calibrated by adjusting the offset angle for long level and turning the SENS screw on the upper surface of each gravimeter. When a galvanometer is connected to the readout socket on the right surface of each gravimeter, the resistance value of a low-pass filter circuit in the galvanometer also contributes to determining the current output sensitivity. As at October-November 2021, the current and voltage sensitivity values of the five gravimeters had been scattered in the range of 0.0526-0.0873 μA/μGal and 0.464-3.560 V/mGal, respectively. We therefore reduced the individual differences of the sensitivity values during the calibration in December 2021, and the current/voltage sensitivity values were standardized to be 0.0631-0.0664 μA/μGal and 2.689-2.953 V/mGal, respectively. Because the sensitivity variation to long level tilt was set to be as small as 2 μGal/sec, it is expected that any of the gravimeters can obtain stable gravity data during both continuous and campaign gravity measurements. We will use these gravimeters with the present status of readout sensitivity, to verify long-term stabilities associated with readout sensitivity and instrumental drift, and response characteristics to environmental disturbances such as microseism and teleseismic waves.