OPERATION MANUAL - Scintrex

The formula given in Equation (B.8) is the one used in the CG-5. However,during periods of high seismicity (caused by microseismic noise), thestandard deviation of the mean is better estimated byERR=------------SDDUR(B.9)if the SEISMIC FILTER is disabled, andSDERR=--------------------( DUR) n(B.10)where n= 1 to 2, if the SEISMIC FILTER is selected.** Displayed reading —Sampling of the gravity signal stops when either DUR reaches the presetREAD TIME or when the MEASURE CLR key is pressed. Up to threefurther corrections: the tilt correction (TIC), the temperature correction(TEC) and the earth tide correction (ETC) are then added to RU to give thereading R which is then displayed.R = RU + TIC + ETC - TEC(B.11)Seismic FilterScintrex firmware versions introduced a new way of gravity signalprocessing, called the SEISMIC FILTER. It is an optional filter. Whendisabled, the gravity signal processing is a. continuous averaging of 1 secondgravity signal samples, whereby all the samples are equally weighted.Sampling of the gravity signal is interleaved with 1 second calibrations. Therepetition rate of calibrations is controlled by CALIBRATE AFTERparameter (usually 12).This signal processing works fine when the seismicity is low - SD (standarddeviation of 1 second gravity signal samples) is less than about 0.05 mGal. Itoffers optimal filtering of the noise from the analogue to digital converter,which is prevalent noise at these low levels of ambient seismic noise. In theScintrex gravity lab, the SD seldom exceeds 0 1 mGal level. Most of the timethis high seismicity is caused by wave action (microseisms) in the AtlanticTheoryB-11CG-5 Manual - part # 867700 Revision 2