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22
4. DATA REDUCTION
4.1 Pressure Calculation
The basic units utilized by Geokon for measurement and reduction of data from Vibrating Wire
Earth Pressure Cells are "digits". Geokon Readouts display "digits" in the Earth Pressure Cell
reading position. Calculation of digits is based on the following equation:
To convert digits to pressure the following equation applies:
Pressure = (Current Reading - Initial Reading) × Calibration Factor
The Initial Reading (R
Calibration Factor (G, usually in terms of psi or kPa per digit) comes from the supplied
Calibration Sheet (a typical calibration sheet is shown in Figure 18). To convert the output to
other engineering units, multiply the Calibration Factor by the conversion multiplier listed in
Table 2.
From →
To
↓
psi
"H
psi
1
.036127 .43275
27.730
"H
O
2
'H
O
2.3108
.08333
2
mm H
0
704.32
25.399 304.788
2
m H
0
.70432 .025399 .304788
2
"HG
2.036
.073552 .882624 .0028959
mm HG
51.706
1.8683 22.4196
atm
.06805 .0024583 .0294996 .0000968
mbar
68.947
2.4908 29.8896
bar
.068947 .0024908 .0298896 .0000981 .098068 .033863 .001333 1.0132
kPa
6.8947
.24908 2.98896 .0098068
MPa
.006895 .000249 .002988 .00000981 .009807 .003386 .000133 .101320
Digits = �
Digits=
Equation 2 - Digits Calculation
P = (R
Equation 3 - Convert Digits to Pressure
) is normally obtained during installation (usually the zero reading). The
0
O
'H
O
mm H
0
m H
2
2
2
.0014223
1.4223
1
12
.039372
39.372
1
.003281
3.281
1
1000
.001
2.8959
.073558
73.558
.0968
.098068
98.068
9.8068
Table 2 - Engineering Units Multiplication Factors
�
2
1
-3
x 10
Period
Or
2
Hz
1000
Or
) × G
- R
1
0
0
"HG
mm HG
atm
2
.49116 .019337 14.696 .014503 14.5039 .14503
13.596
.53525
406.78
1.133
.044604 33.8983 .033456 33.4558
345.32
13.595
10332
1
.34532 .013595 10.332 .010197 10.197
1
.03937
29.920 .029529 29.529
25.4
1
760
.03342 .0013158
1
33.863
1.3332
1013.2
3.3863
.13332 101.320
mbar
bar
kPa
145.03
.40147
401.47
4.0147
4016.1
.3346
10.197
10197
101.97
101970
.10197
101.97
.2953
.75008
750.08
7.5008
7500.8
.0009869 .98692 .009869
1
1000
10
.001
1
.01
.1
100
1
.0001
.1
.001
MPa
334.6
295.3
9.869
10000
10
1000
1
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