FOVsD is the camera's field of view in the direction of scanning and speed is the
average speed. This calculation assumes that the surface temperature cooling profile at
every point is linear, which is not the case. The results are reported in this format for
ease of comparison between FRP systems.
Controlling the speed of the cart during each scan was difficult. Figure 4-8 shows
the resulting ATbackground along the leading and trailing edge of each thermal image vs.
position for Girder 3 and Girder 6. The leading edge curve represents ATbackground
measured just after an area enters the thermal image. The trailing edge curve represents
ATbackground measured just before the same area leaves the image. The average time
between these two curves can be calculated as t' in equation 4. The significant
fluctuation observed in each curve demonstrates the sensitivity of ATbackground to cart
speed. In areas where the cart was pushed slowly, there was an increase in ATbackground
while areas in which the cart was moved more quickly experienced a decrease in
ATbackground. The standard deviation of ATbackground along the leading edge for Girder 3, 4,
5, and 6 was 1.4, 2.4, 1.5, and 1.90C, respectively.
16 T 18 -- Leading Edge
14- Leading Edge 16 --
a 12- 14-
o 12
10
0 8 0
STrailg 6 6 Trailing Edge
S4 Tiling Edge 4--
2 2
0I I 0 I I
0 200 400 600 0 200 400 600
Position (cm) Position (cm)
A B
Figure 4-8. Background temperature increase vs. position along length of girder. A)
Girder 6. B) Girder 3