Geokon 4911, Руководство по установке, Страница: 17 / 27

11
4. DATA REDUCTION
4.1 Strain Calculation
The basic units utilized by Geokon for measurement and reduction of data are “digits”.
Calculation of digits is based on the following equation:
Digits =
�
1
T
�
2
x 10
-3
or Digits
=
Hz
2
1000
Equation 1 - Digits Calculation
Where;
T is the period in seconds.
Hz is the frequency in cycles per second.
To convert digits to strain the following equation applies:
ε
apparent = (R
1
- R
0
) × C
Equation 2 - Apparent Strain
Where;
R
0
is the initial reading in digits, usually obtained at installation or at the commencement of a
test.
R
1
is the current reading in digits.
C is the calibration factor from the supplied calibration report. (For an example of a typical strain
meter calibration report see Figure 10 in Appendix D.)
For example: Assuming an initial reading (R
0
) of 8000 digits, a current reading (R
1
) of 7700, and
a calibration factor (C) of 0.343 microstrains per digit; the strain calculation would be as follows:
ε
apparent = (7700 - 8000)
× 0.343 = - 102.9 µε (compression)
4.2 Temperature Correction
The assumption with strain meters embedded in concrete is that the strain in the meter is equal
to the strain in the concrete . However, when the temperature changes the concrete expands and
contracts at a rate slightly less than the rate of the steel of the vibrating wire. The coefficients of
this expansion are shown in the table below.
Steel (K
steel
):
12.2 ppm/°C 6.7 ppm/°F
Concrete (K
concrete
):
≈ 10 ppm/°C ≈ 5.5 ppm/°F
Difference (K): 2.2 ppm/°C 1.2 ppm/°F
Table 1 - Thermal Coefficients