OPERATION MANUAL - Scintrex

Compensation and Correctionssample of the reading.The reason for two modes of operation is that the tilt sensors have a relativelyfast response (typically a few seconds) up to within approximately 5 arcsecof the final value and then it takes up to a minute to come to within onearcsec of the final value.If the Autograv is on a solid base and it does not move during the reading,then the OFF mode will give the most accurate result as the tilt sensors willhave more time to settle before a compensation is applied.If the instrument is on a soft base and moves during a reading, then it ispreferable to select the continuous correction mode.It should be noted that over a period of several hours, some tilt changes mayarise from movement of the elastomer in the shock isolators (used to protectthe sensor from severe shocks). This not relevant for the Reading mode. Inthe Base Station mode, however, these changes are corrected by the tiltcorrection function, regardless of whether or not the tilt correction function isenabled or disabled.Temperature Compensation (TEC)The fused quartz mainspring is the most temperature sensitive component inthe gravity meter with a coefficient of approximately - 130 mGal/°K (springbecomes stronger as the temperature increases). This spring is protected fromambient temperature changes by a two stage thermostat which maintains thespring temperature Ts constant to within 0.5mK under normal operatingconditions.The changes in Ts are measured using a temperature sensor in good thermalcontact with the mainspring. The output of the temperature bridge isconverted to a digital signal, TEMP shown in the figure on page B-3 and thisis converted to the temperature compensation signal.TheoryTEC = TEMPCO x TEMP(B.21)TEMPCO is the instrument temperature coefficient in mGal/mK. It ismeasured during the production of each instrument and is entered through thekeypad. A new value of TEC is computed and applied after the last samplehas been taken.B-19CG-5 Manual - part # 867700 Revision 2