11
4.2 Strain Calculation
The gage length of the standard strand meter is 203.2 mm, (eight inches). The strain in
microstrains
μ
is given by the equations:
Where D is in mm:
μ = (D/203.2) x 10
6
microstrain
Equation 3 - Strand Calculation in Millimeters
Where D is in inches:
μ = (D/8) x 10
6
microstrain
Equation 4 - Strand Calculation in Inches
4.3 Temperature Correction
The Model 4410 Vibrating Wire Strandmeters have a small coefficient of thermal expansion;
therefore, in many cases correction is not necessary. However, if maximum accuracy is desired
or the temperature changes are large corrections may be applied. The temperature coefficient of
the strand to which the Strandmeter is attached should also be taken into account. By correcting
the transducer readings for temperature, changes the temperature effect on the strand can be
isolated and quantified.
The following equation applies:
Dcorrected = ((R
1
- R
0
)
×
G) + ((T
1
- T
0
)
×
K)
Equation 5 - Thermally Corrected Deformation Calculation
Where;
R
1
is the Current Reading.
R
0
is the Initial Reading.
G is the Calibration Factor.
T
1
is the Current Temperature.
T
0
is the Initial Temperature.
K is the Thermal Coefficient for the Transducer, (see Equation 6).
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 determination of
the proper Thermal Coefficient based on the following equation: