Geokon 4580, Instruction Manual

Page: 15 / 25

9
4. DATA REDUCTION
4.1 Pressure Calculation
The basic units utilized by Geokon for measurement and reduction of data from vibrating wire
pressure transducers are the “digits” displayed on the GK-404 or GK-405 reading box.
Calculation of digits is based on the following equation:
Digits =
�
1
Period
�
2
×
10
-3
or Digits
=
Hz
2
1000
Equation 1 - Digits Calculation
For example, a transducer reading 9000 digits on channel B of the GK-404 or GK-405 readout
corresponds to a period of 333.3 µ s and a frequency of 3000 Hz. Digits are directly proportional
to wire tension and applied pressure.
To convert digits to pressure using a linear calibration coefficient the following equation applies:
(See Appendix C for use of second order polynomial)
P
uncorrected
= (R
1
– R
0
) × G × F
1
Equation 2 - Convert Digits to Pressure
Where:
R
0
represents the initial reading taken at installation (usually the zero reading).
R
1
represents the current reading.
G is the calibration factor required to convert from “digits” to the engineering units given on the
calibration report. (See Appendix D for a sample calibration report.)
F
1
is an optional multiplier to convert to any other required engineering units (see Table 1).
For example :
If;
The initial reading on channel B (R
0
) = 2509,
The current reading (R
1
) = 7023
The calibration factor (G) = -0.0001954 psi/digit.
Then;
Pressure = (7023 - 2509) × -0.0001954 = 0.882 psi