MODEL 4420 VIBRATING WIRE CRACKMETER
| MODEL 4420HT – HIGH TEMPERATURE VERSION |
19
APPENDIX C.
MODEL 4420HT – HIGH TEMPERATURE
VERSION
Model 4420HT is a high-temperature crackmeter, rated to 200 °C. This model is
supplied with 316 stainless steel U-joints on the ends, as opposed to the rod end
bearings installed on standard crackmeters. Due to the U-joint configuration, the
overall instrument assembly length is 35 mm (1.375") longer, which you must
add when determining anchor spacing distance using in Table 1.
The epoxied diameter is slightly larger with the HT version due to added
waterproofing and strain relief for the Teflon cable. This results in a space of
about 14.5 mm (0.569") between the U-joint and the outer diameter of the
epoxy. The standard spacer supplied with anchors as shown in Figure 5 and
Figure 6 is about 12.7 mm (.500"); therefore, interference between the epoxied
area and the mounted surface may occur. To ensure this doesn’t happen, either
rotate the assembly 180 degrees on its axis, or use the larger supplied spacers.
4420HT crackmeters are supplied with a high temperature thermistor that has a
range of -55 to +300 °C, and an accuracy of ±0.5 °C. To convert ohms to
temperature, use Equation 7 or Table 8 below.
Thermistor Type: US Sensor 103JL1A
Resistance to Temperature Equation:
EQUATION 7:
Model 4420HT 10KΩ Thermistor Resistance
Where:
T
= Temperature in °C
LnR
= Natural Log of Thermistor Resistance
A
= 1.127670 x 10
-3
B
= 2.344442 x 10
-4
C
= 8.476921 x 10
-8
D
= 1.175122 x 10
-11
Note:
Coefficients optimized for a curve
J
Thermistor over the temperature
range of 0 °C to +250 °C.
T =
1
– 273.15
A+B(LnR)+C(LnR)
3
+D(LnR)
5