MODEL 4420 VIBRATING WIRE CRACKMETER
| DATA REDUCTION |
15
Where:
R
1
is the current reading
M
is the multiplier, from Table 5
B
G
is the linear gauge factor from the supplied calibration sheet.
TABLE 5:
Thermal Coefficient Calculation Constants
Consider the following example using a Model 4420-200 mm crackmeter:
R
0
= 4773 digits
R
1
= 4589 digits
T
0
= 20.3 °C
T
1
= 32.9 °C
G
= 0.04730 mm/digit
K
= (((4589 x 0.000396) – 0.4428) x 0.04730) = 0.065011
D
corrected
= ((
R
1
–
R
0
) x
G
) + ((
T
1
–
T
0
) x
K
)
D
corrected
= ((4589 – 4773) x 0.04730) + ((32.9 – 20.3) x 0.065011)
D
corrected
= (–184 x 0.04730) + 0.819
D
corrected
= –8.7032 + 0.819
D
corrected
= –7.8842 mm
The temperature coefficient of the mass or member to which the crackmeter is
attached should also be taken into account. Use the temperature coefficient of
the mass or member, combined with the changes in temperature from initial to
current readings, to determine thermal effects of the mass or member.
5.3
ENVIRONMENTAL FACTORS
Because the purpose of using a crackmeter 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.
Model:
5:
Multiplier (M):
Constant (B):
4420-3 mm (0.125")
0.000520
3.567
4420-12 mm (0.5")
0.000375
1.08
4420-25 mm (1")
0.000369
0.572
4420-50 mm (2")
0.000376
0.328
4420-100 mm (4")
0.000398
0.0864
4420-150 mm (6")
0.000384
-0.3482
4420-200 mm (8")
0.000396
-0.4428
4420-300 mm (12")
0.000424
-0.6778