Remote Health Monitoring for Asset Management

array was mounted horizontally in the laboratory with the infrared lamp directed at the array
from a distance of approximately 18 inches for a typical test.
Figure 5.4. Schematic diagram of laboratory test set-up.
To establish the response time of the sensor array, the lamp was placed adjacent to sensor 2,
approximately 10 inches from the end of the sensor array as shown in Figure 5.4, location 1. The
output of the sensor array was monitored at 1-minute intervals. Figure 5.5 shows the initial
temperature along the sensor array and the array output for various time periods following the
application of heat. As shown in the figure, the array begins to respond at the 7-minute mark of
the test, when sensor 1 changes its output by 0.5 ºC, the minimum resolution interval for the
digital sensors. The figure shows the output of the array at time intervals ranging from 7 minutes
after test initiation up to 4 hrs after test initiation. Sensor 1 reached maximum ~4 hours after the
test initiation, and maintained that temperature.
Figure 5.6 shows the performance of sensors 1, 6, 11 and 30 during the test. As shown in the
figure, when the test is initiated (the heating lamp is turned on) the sensor responds to the
external heat application and measures the heating of the sensor array up to a maximum
temperature of 33.0 ºC approximately 4 hrs later. The temperature distribution along the length
of the pile measured by the remaining sensors in the array was expected to show a thermal
gradient as the distance from the heat source to the individual sensor increased. Figure 5.6
shows that a sensor located 87 inches from the heat source (sensor 30) showed no reaction to the
application of heat at the end of the pile, while sensor 6 (15 in. from the heat source) and sensor
11 (30 in. from the heat source) responded to the application of heat in an expected manner,
increasing less rapidly over the course of the testing.
30