Laboratory method of detecting and measuring circular errors in LaCoste and Romberg model-D gravity meters

Abstract

SUMMARY We have developed in the laboratories of the Geological Survey of Canada an automatic technique to search for periodic errors in LaCoste and Romberg model-D gravity meters. This computer-controlled method samples the output of an instrument at every 20 pGal (1 pGal= 10 nm s-*) and analyses the results as they are gathered. The technique was first developed and tried out on one instrument, D-28, and later applied to three other instruments. Results have been encouraging as analysis revealed the presence of periodic errors in every instrument. The amplitudes of the signals detected ranged from 0.1 pGal for short periods to more than 2 pGal for the long period of 3.25 mGal. In addition to the expected periods, other short periods have been found to have important amplitudes. Further tests have also shown that the sampling interval can be increased to speed up calibration. In view of the increasing use of feedback systems with LaCoste and Romberg instruments, periodic errors will still have to be accurately measured in an efficient manner as the range of feedback systems does not exceed some of the longer periods found in the dial system which seems to be the main cause of the periodic errors.