OPERATION MANUAL - Scintrex

Example: —Because of the positive drift rate of the CG-5 gravity sensor, the uncorrectedgravity readings at the fixed locations gradually increase in value. The lineardrift of the CG-5 sensor is caused by an unavoidable creep of the quartzspring, whose length under tension increases, on the average, by 0.5 ppm/day at the operating temperature of 60°C. A typical sensor with the drift rateof 0.5 mGal/day will reach the high end of the measurement range, at thelatitude of 60 degrees, in about 20 years. If used at lower latitudes, as mostgravimeters are, the typical CG-5 service life will be even longer.You may estimate the remaining service life of your meter in the followingway:1. Calculate the value SU max for your meter.2. Obtain the gravity reading at your location.3. If you are planning to use your meter at higher latitudes than your presentlatitude, evaluate from Table 1 the gravity difference between your presentlatitude and the highest latitude at which you will be using your meter. Addthis difference to the reading obtained in Step 2. to obtain the value SU m .4. The remaining service life expressed in days is calculated by dividing thedifference (SU max - SU m ) by the value of the linear drift rate of your CG-5.1. You have calculated for your meter from Equation (B.2)on page B-6:SUmax = 8800 mGal2. The drift rate of your meter is: 0.51 mGal/day.Theory3. Assuming that you are at latitude of 50°.4. You have measured SU = 5012 mGal.5. Assuming that you will be using your meter up to latitudes of 60°.6. Giving SU m = (5012 + 847) mGal, (see Step 3.).7. Then the number of remaining service days is: (8800 - 5012 - 847)/0.51 =5767.g=g e × [ 1+b×sin 2 2θ]– [ b1 × sin 2 2θ]gravity at latitude θ (B.3)B-7CG-5 Manual - part # 867700 Revision 2