11
Equation 3 - 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 (see calibration sheet).
Consider the following example using a Model J2-25 mm Crackmeter;
R
0
= 4773 digits
R
1
= 4589 digits
T
0
= 20.3° C
T
1
= 32.9° C
G= 0.00555 mm/digit
K = (((4589
0.000301) + 0.911)
0.00555 ) = 0.0127
D
corrected
= ((R
1
- R
0
)
C) + (((T
1
- T
0
)
K)
D
corrected
= ((4589 - 4773)
0.00555) + ((32.9 - 20.3)
0.0127)
D
corrected
= (-184
0.00555) + 0.160
D
corrected
= -1.021 + 0.160
D
corrected
= -0.861 mm
As can be seen from the above example, the corrections for temperature change are very small and
can usually be ignored.
4.3. Environmental Factors
Since the purpose of the crackmeter installation is to monitor site conditions, factors which may
affect these conditions should always be observed and recorded. Seemingly minor effects may have
a real influence on the behavior of the structure being monitored and may give an early indication
of potential problems. Some of these factors include, but are not limited to: blasting, rainfall, tidal
levels, excavation and fill levels and sequences, traffic, temperature and barometric changes,
changes in personnel, nearby construction activities, seasonal changes, etc.
5. TROUBLESHOOTING
Maintenance and troubleshooting of CGEO Vibrating Wire Crackmeters is confined to periodic
checks of cable connections and maintenance of terminals. The transducers themselves are sealed
and cannot be opened for inspection. However, note the following problems and possible solutions
should difficulties arise. Consult the factory for additional troubleshooting help.
Symptom: Crackmeter Readings are Unstable
Is the readout box position set correctly? If using a datalogger to record readings automatically
are the swept frequency excitation settings correct?
