MODEL 4420 VIBRATING WIRE CRACKMETER
| DATA REDUCTION |
13
5.
DATA REDUCTION
5.1
DISPLACEMENT CALCULATION
The basic units utilized by
GEOKON
for measurement and reduction of data from
vibrating wire crackmeters are digits. Calculation of digits is based on the
following equation:
EQUATION 1:
Digits Calculation
To convert digits to displacement the following equation applies:
D
uncorrected
=
(R
1
–
R
0
) x G x F
EQUATION 2:
Displacement Calculation
Where:
R
1
is the current reading.
R
0
is the initial reading, usually obtained at installation.
G
is the gauge factor, usually millimeters or inches per digit (see Figure 12).
F
is an optional engineering units conversion factor (see the table below).
TABLE 4:
Engineering Units Conversion Multipliers
For example, the initial reading
R
0
, at installation of a crackmeter is 2500 digits.
The current reading,
R
1
, is 6000. The gauge factor is 0.006223 mm/digit. The
displacement change is:
D
uncorrected
=
(6000
–
2500) x 0.006223 x +21.78
EQUATION 3:
Displacement Change
Note that increasing readings (digits) indicate increasing extension.
To use the polynomial gauge factors given on the calibration sheet, use the
value of
R
0
and Gauge Factors
A
and
B
with
D
set to zero to calculate the new
value of
C
. Then substitute the new value of
R
1
and use
A
,
B
, and the new value
of
C
to calculate the displacement
D
.
From
To
4:
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