OPERATION MANUAL - Scintrex

If, after many years of service, your CG-5 has drifted out of range, then thespring position may be reset by a routine procedure at the Scintrex plant.Processing of the Gravity SignalWhile reading this section, please also refer to the Signal Flow diagram onpage B-3.The input to the gravity analog to digital converter (ADCL) is switchedbetween V fb , the gravity transducer output and V cal , the stable calibrationvoltage.** When the instrument is in the SETUP mode (after the SETUP key ispressed once), the calibration voltage is connected to ADCL. In this mode,the value of V cal can be viewed on the display under the heading G R AV.** In the READ mode, (after the MEASURE CLR key is pressed) the input toADC 1 is held at Vcal for one second (during P A U S E) then switched toVfb for x one-second samples. It is then switched back to Vcal for onesample then to Vfb for x samples and so on until the reading is terminated.The value of x is entered under the Autograv setup at the CAL AFTERprompt. The output of ADC 1 is termed SC when Vcal is applied and SFwhen the V fb is applied.Uncorrected sample —The calibration voltage and other calibration factors are then applied to thegravity signal by the function f cal in order to give an uncorrected sampleTheorySU=( ) GCAL1⎛-------SF ⎞ SF=⎝SC⎠+ GCAL2⎛-------⎞ 2⎝SC⎠f calSC,SF(B.4)SF is divided by the most recent value of SC to correct for any drift in thescale factor of ADC1. The factors GCAL1 and GCAL2 are the instrumentcalibration factors which are entered via the keypad. They take into account asmall quadratic non-linearity inherent in the ADC and in the conversion fromelectrostatic feedback voltage to force.B-9CG-5 Manual - part # 867700 Revision 2