Geokon 6300, Instruction Manual, Page: 17 / 24

11
4. DATA REDUCTION
4.1 Inclination Calculation
Inclinations are measured in digits on Position B on the Geokon readout. The output of the VW
tilt sensor is proportional to the sine of the angle of tilt. For small angles θ and sin θ are the same,
so the relationship between output digits and the amount of tilting, (change of the angle of
inclination), ∆θ , is given by the equation:
∆θ = ∆ sin θ = (R
1
− R
0
) G degrees tilt
Equation 1 - Calculation of Tilt (Linear)
Where;
R
1
is the current reading in digits
R
o
is the initial reading in digits
G is the Linear Gauge Factor in degrees tilt/digit given on the calibration report supplied with the
sensor. (A sample calibration report is shown in Appendix E.)
The linear equation works very well for inclinations of less than four degrees. More than this and
the linearity errors start to increase beyond 0.5% FS. The error incurred by using the linear
equation is shown on the calibration chart.
For better accuracy at larger inclinations use the polynomial equation: This uses a second order
curve to approximate the sine curve.
θ = R 2 A + RB + C degrees tilt
Equation 2 - Calculation of Tilt (Polynomial)
Where A, B and C are the coefficients supplied on the calibration report. Calculate θ
1
by
substituting R = R
1
in the formula and then calculate θ
0
by substituting R = R
0
then subtract to
find the difference ∆θ = ( θ
1
- θ
0
).
4.2 Temperature Correction
The Model 6350 Tiltmeter has a slight temperature sensitivity on the order of -0.5 digit per °C
rise, i.e. the reading falls by 0.5 digits for every one °C rise of temperature. The temperature
correction is:
+0.5G(T
1
-T
0
) degrees tilt
Equation 3 - Temperature Correction
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 that will show up in the readings. The gauge 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.