Evaluation - CPI CMP 200 Series Service Manual

CPI Canada Inc
5.0 H.V.L. EVALUATION
1. Be sure the X-ray source assembly (X-ray tube and beam limiting device) is fully assembled and
functional.
2. Use the test setup as per figure 1.
3. Set the generator as follows: 3 point generators, 80 kV, 200 mA, 50 ms, large focus. For 2 point
generators use 80 kV, 200 mA if this can be set, and 10 mAs.
4. Take a series of three exposures and record the dose K (kerma) values in mGy in table 10.
Calculate and record the average of the three exposures.
5. Place 2 mm of Al on top of the lead diaphragm (total of 2 mm added), repeat the exposure and
record the K value in table 10.
6. Place an additional 1 mm of Al on top of the lead diaphragm (total of 3 mm added), repeat the
exposure; and record the K value in table 10.
7. Place an additional 3 mm of Al on top of the lead diaphragm (total of 6 mm added), repeat the
exposure; and record the K value in table 10.
8. The relative transmission for the average of the three K values where no Al was added is
assigned a value of 1.00. Using that base, assign relative transmission values to the remaining K
values. For example, if the average K value was 2.15 and has a relative transmission factor of
1.00, then 1.41 mGy will have a relative transmission of 1.41 / 2.15 = 0.66.
9. Plot the relative transmission values in figure 1. This should produce a straight line on the graph
since the X-axis is logarithmic.
10. Interpolate to determine the HVL. The Al thickness at a relative transmission of 0.5 will be the
required HVL value.
11. Repeat steps 4 to 10: 3 point generators, 100 kV, 200 mA, 50 ms, large focus. For 2 point
generators use 100 kV, 200 mA if this can be set, and 10 mAs. Use table 11 to record the values
and figure 2 to plot the results
12. Table 12 and figure 3 show example HVL determination.
Use and disclosure is subject to the restrictions on the title page of this CPI document.
X-Ray Generator Service Manual Supplement
Reproducibility, Linearity, & HVL Testing
740917-00 Rev. C Page 9