OPERATION MANUAL - Scintrex

material and fasten it down with a flexible binding material (e.g. seat belt orrubber-based cord).• The CG-5 is an extremely sensitive and precise scientific instrument. It iscapable of measuring gravity changes that would result in a 10 -10 metreschange in the proof mass vertical position. Note that the hydrogren atom hasa diameter of the same size. However, it is inherently robust and wellcapable of providing accurate relative gravity values under relatively rough(but normal) field handling.In a controlled shock test, one meter was dropped from various heights to ahard floor. The drops from 40mm, resulting in a 20g peak deceleration atthe sensor location, resulted in level shifts of less than 0.01 mGal. Theshock isolators and the stops limiting the proof mass movement reduce theeffect of shocks on the sensor. Nevertheless, the meter does have limits, sothat careful handling during measurement generally yields better results.• To obtain the highest accuracy after unavoidable rough transport, allow theAutograv to settle for a few minutes after being leveled on its tripod beforestarting a reading. If rough handling has occurred, there may be a slight (butnoticeable) drift for only a few minutes after leveling.• Whereas the CG-5 may be placed in any orientation (tilted on its side)without damage, it is preferable to keep it upright in storage or duringshipment. When at rest, it should be kept leveled (see above) for best results.If for some unavoidable reason, these precautions have not been followed,then allow time for the CG-5 readings to stabilize at the first station. Byobserving the sequential readings (e.g. 60 or 120 seconds averaging), youcan tell if the unit is stable by evaluating their convergence.Minimizing Motion NoiseMotion of the base of support of the meter may induce noise and readingerrors. Such motion may be caused (and minimized) by:Poor ground conditions - Soft ground, tree root movement and settling ofthe tripod. These are improved by the Tilt Correction (continuous or not). Formore information, see Appendix B, “Theory of Operation”.Microseismic noise - This is due to the motion of the continental crust as aneffective wave guide for seismic surface waves of (usually) a 4 to 8 secondperiod. These effects may be caused by long-period ocean wave strikingcoast lines. They are most severe in islands in the seas (e.g. Ireland) but mayOperations4-3CG-5 Manual - part # 867700 Revision 2