Geokon 6350, Installation Manual, Page: 21 / 26

15
4. DATA REDUCTION
4.1 Tilt Calculation
Tilts are measured in digits on Position B of either the GK-404 or GK-405 Readout Box. The
relationship between these digits and the change of the angle of inclination (tilt) is given by the
equation:
∆θ
= (R
1
−
R
0
) G degrees
Equation 1 - Digits Calculation
Where;
R
1
is the current reading in digits.
R
0
is the initial reading in digits.
G is the Calibration Factor in degrees/digit.
The linear equation works very well for tilt angles of less than two degrees. More than this and
the linearity errors increase. The error incurred by using the linear equation is shown on the
calibration chart.
For better accuracy at larger inclinations, use the polynomial equation:
θ
= R
2
A + RB + C
Equation 2 - Polynomial Equation
Where;
A, B and C are the coefficients supplied on the calibration report. Calculate
θ
for R = R
1
and R =
R
0
then subtract to find the difference
∆θ
for (R
1
– R
0
).
4.2 Temperature Correction
The Model 6350 Tiltmeter has a very slight temperature sensitivity on the order of – 0.5 digit per
°C rise, i.e. the reading falls by 0.5 digits for every 1 °C rise of temperature. The temperature
correction is:
+K (T
1
-T
0
) degrees
Equation 3 - Temperature Correction
Where K = 0.5G.
Normally, corrections are not applied for this small effect because the structure being monitored
usually is affected to a much greater degree. An important point to note, also, is that sudden
changes in temperature will cause both the structure and the Tiltmeter to undergo transitory
physical changes, which will show up in the readings. The gage temperature should always be
recorded for comparison, and efforts should be made to obtain readings when the instrument and
structure are at thermal equilibrium. The best time for this tends to be in the late evening or early
morning hours.