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16
6.3 Readout Box Positions D & E
Reading for Models 4200 (Channel D) and 4202 (Channel E) are displayed on the readout box
directly in microstrain based on the theoretical equation:
Where;
f is the frequency in digits.
G is the theoretical gage factor, equal to 3.304 for the 4200 gage and 0.3910 for the 4202 gage.
In practice, the method of wire clamping shortens the vibrating wire slightly, causing it to over
register the strain. This effect is removed by applying the batch gage factor supplied with each
gage. With the batch gage factor applied the apparent change in strain shown on the readout box
is equal to:
Where;
R
is the initial reading
0
R
is the current reading from the readout box, taken in position D or E. (Note: when (R
1
positive, the strain is tensile.)
B is the batch gage factor suppled with each gage.
6.4 Strain Resolution
When using the GK-403 Readout on channel setting "D" (4200/4200HT) or "E" (4202) the strain
resolution is ±0.1 microstrains throughout the range of the gage. For Models 4210, 4212 and
4214, (channel B), the resolution is 0.1 times the supplied gage factor. However, for some gages
the reading may fluctuate by one digit, so this resolution may not be useful.
6.5 Temperature Corrections
Temperature variations of considerable magnitude are not uncommon, particularly during
concrete curing; therefore, it is always advisable to measure temperatures along with the
measurement of strain. Temperature induced expansions and contractions can give rise to real
changes in the stress of the concrete if the concrete is restrained in any way. These stresses are
superimposed on any other load related stresses.
µε
= G (Δf
× 10
2
theory
Equation 2 - Theoretical Strain
µε
− R
= (R
apparent
1
Equation 3 – Apparent Strain
−3
)
)B
0
− R
) is
1
0
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