Geokon 4422, Instruction Manual

Page: 15 / 21

9
4.2 Temperature Correction
Because Geokon’s Vibrating Wire Displacement Transducers have a small coefficient of thermal
expansion, in many cases correction may not be necessary. However, if maximum accuracy is
desired, or the temperature changes are extreme (>10 °C), a correction may be applied based on
the following equation:
Dcorrected = ((R
1
- R
0
)
×
G) + ((T
1
- T
0
)
×
K)
Equation 3 - Thermally Corrected Deformation Calculation
Where;
R
1
is the current reading.
R
0
is the initial reading.
G is the linear gage factor.
T
1
is the current temperature.
T
0
is the initial temperature.
K is the thermal coefficient (see Equation 4).
The temperature coefficient of the mass or member to which the Crackmeter is attached should
also be taken into account. By correcting the transducer for temperature changes the temperature
coefficient of the mass or member may be distinguished.
Tests have determined that the thermal coefficient, K, changes with the position of the transducer
shaft. Hence, the first step in the temperature correction process is to determine the proper
thermal coefficient based on the following equation:
K = ((R
1
×
M)
+
B)
×
G
Equation 4 - Thermal Coefficient Calculation
Where;
R
1
is the current reading.
M is the multiplier from Table 3.
B is the constant from Table 3.
G is the linear gage factor from the supplied calibration sheet (Figure 6).
Model: 4422
Multiplier (M): 0.000471
Constant (B): 0.3562
Table 3 - Thermal Coefficient Calculation Constants