Fluke Biomedical 35080M - Manual (Page 46)

Low Range Filter Pack Option (38237)
Filtration Effect Correction
8
8-3
8.5 Filtration Effect Correction
The Low Range Filter Pack (38237) is calibrated at 2.5 mm Al total filtration. Measurements made at
other filtration values require a correction to the measured reading. Corrections for filtration are made
using the correction curve shown in Figure 8-1. Corrections are made by subtracting the total filtration of
the X-ray machine being measured from 2.5 mm Al, multiplying the result by the value read off the chart
for the measured kVp, and adding this result to the measured kVp.
Example
A reading of 49 kVp is obtained from a Model 35080M kVp Divider using a Low Range Filter Pack
(38237). The X-ray system has 3.3 mm Al total filtration. The filtration effect curve of Figure 8-1
indicates a filtration effect of 0.5 kVp per mm Al at 49 kVp. The difference in filtration, 2.5 - 3.3 = -0.8
mm Al, is multiplied by the correction value to yield -0.8 x 0.5 = -0.4 kVp. This number is then added to
the apparent reading to obtain the actual kVp, which is 49 kVp + (-0.4 kVp) = 48.6 kVp.
Figure 8-1. Low Range Filter Pack (38237) Filtration Effect Correction Curve
8.6 Linearity Correction
Corrections for the linearity of the Low Range Filter Pack (38237) can be made by taking the
measured output of the Model 35080M kVp Divider and adding the value in kVp shown on the
curve in Figure 8-2. For best accuracy, a filtration correction should be made prior to the linearity
correction. If the difference in total filtration from the calibration standard of 2.5 mm Al is small,
however, linearity corrections alone may be sufficient.
Example
The Model 35080M kVp Divider with a Low Range Filter Pack (38237) has a reading of 45 kVp. From
the chart, a kVp Correction value of -0.2 kVp is obtained. Assuming filtration corrections are not
required for this X-ray system, the actual kVp is 45 + (-0.2) = 44.8 kVp.
Low Range Filter Pack (38237)
Filtration Effect
-0.5
0
0.5
1
1.5
2
2.5
3
30 40 50 60 70 80 90 100
Model 35080B kVp Reading
kV
p P
e
r mm A
l