Geokon 4422, Instruction Manual

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8
4. DATA REDUCTION
4.1 Displacement Calculation
The basic unit utilized by Geokon for measurement and reduction of data from Vibrating Wire
Displacement Transducers is "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 use Equation 2.
Duncorrected = (R
1
- R
0
)
×
G
×
F
Equation 2 - Deformation Calculation
Where;
R
1
is the current reading.
R
0
is the initial reading, usually obtained during installation (see Section 2.3).
G is the gage factor, usually millimeters or inches per digit.
(See the example calibration sheet shown in Figure 6.)
F is an optional engineering units conversion factor, see Table 2.
From
→
To
↓
Inches
Feet
Millimeters
Centimeters
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 2 - Engineering Units Conversion Factors
For example, if the initial reading (R
0
) is 4000 digits, the current reading (R
1
) is 5000, and the
gage factor is 0.001077 mm/digit, then the deformation change is calculated as follows:
Duncorrected = (5000
−
4000)
×
0.001077 = +1.077 mm
(Note that increasing readings (digits) indicate that the crack is widening.)
To use the Polynomial Gage factors given on the Calibration Sheet: Use the value of R
0
and
Gage Factors A and B, with the displacement (D) set to zero, to calculate the new value of C.
Next, substitute the new value of R
1
, and use A, B, and the new value of C, to calculate D.