9
4. DATA REDUCTION
4.1 Deformation Calculation
The basic units utilized by Geokon for measurement and reduction of data from Vibrating Wire
Deformation Meters are "digits". The units displayed by all Readout Boxes in position "B" are
digits. Calculation of digits is based on the following equation:
Digits =
�
1
Period
�
2
x 10
-3
or Digits
=
Hz
2
1000
Equation 1 - Digits Calculation
To convert digits to deformation the following equation applies;
Deformation
=
(Current Reading - Initial Reading)
×
Calibration Factor
×
Conversion Factor
Or
D = (R
1
- R
0
)
×
G
×
F
Equation 2 - Deformation Calculation
Where;
D is the Deformation in millimeters or inches.
R
1
is the Current Reading.
R
0
is the Initial Reading usually obtained at installation.
G is the Calibration Factor, usually in terms of millimeters or inches per digit.
F is an engineering units conversion factor (optional), see Table 1.
From
→
To
↓
Inches
Feet
Millimeters
Centimeter
s
Meters
Inches
1
12
0.03937
0.3937
39.37
Feet
0.0833
1
0.003281
0.03281
3.281
Millimeters
25.4
304.8
1
10
1000
Centimeters
2.54
30.48
0.10
1
100
Meters
0.0254
0.3048
0.001
0.01
1
Table 1 - Engineering Units Conversion Multipliers
For example, the Initial Reading (R
0
) at installation of a strandmeter is 4783 digits. The Current
Reading (R
1
) is 5228. The Calibration Factor is 0.0006194 mm/digit. The deformation change is
D = (5228
−
4783)
×
0.0006194 = +0.2756 mm
Note that increasing readings (digits) indicate increasing extension.
A typical Calibration Sheet for a three-millimeter range strand meter is shown on the next page.