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4. DATA REDUCTION
4.1 Displacement Calculation
The basic units utilized by Geokon for measurement and reduction of data from Model 3900
Embedment Strain Gauges are mV/V
If a GK-502 readout box is in use mV/V can be displayed directly.
The displacement D is given by the equation:
Where;
D is the displacement in the units given on the calibration report provided with the instrument.
R
is the initial GK-502 reading in mV/V.
0
R
is the current GK-502 reading in mV/V.
1
C is the calibration factor in millimeters/mV/V, or inches/mV/V as supplied on the Cal Sheet.
(See Appendix C. for a sample calibration report.)
If a regulated power supply and a millivoltmeter are used, then calculate the mV/V by dividing
the displayed millivolt output by the voltage input measured at the sensor using the remote signal
leads, (Green and Green' Black).
4.2 Strain Calculation
To calculate the strain ε, divide the measured displacement D by the gauge length L.
The standard length for L is 203 mm (Eight inches)
Example: Using a GK-502, R
Strain ε = ((-0.5563-(-0.8640) x 0.05193/8 = +2000 microstrain (tension)
Note that an increasing reading denotes a tensile strain.
D = ((R
- R
1
Equation 1 - Displacement
= -0.8640 and R
= -0.5563, C = 0.05193 inches/mV/V.
0
1
) × C
0
3
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