LORAD AFFINITY Series, Service Manual

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P/N 9-500-0255 4-19
Service Manual
Chapter 4: Calibrations and Performance Checks
Automatic Exposure Control System Calibration
2. Set unit to Calibration Screen #3, set the HTC C-THK threshold for 1.0 cm.
3. Set unit to Calibration Screen #2.
4. Install the 18 x 24 cm Bucky onto the IRSD and insert a loaded cassette. Always use the
same cassette and Bucky for all calibration steps.
5. Set the unit for an Auto-Time exposure at 25 kV, Large focus, Mo filter. Set the Film data
field to the screen-film combination loaded in the cassette.
6. Place 3.0 cm of BR-12 or PMMA acrylic on the Bucky, centered laterally, and extending
approximately 1.0 cm over the chest wall edge.
7. Place the AEC detector in the position closest to the chest wall. Take an exposure,
develop the film, then measure the optical density (OD).
Note… Always measure the Optical Density with the lower edge of the film flush
with the front edge of the Densitometer and centered side-to-side
(approximately 5.0 cm into film plane).
8. Make Gain adjustments to calibrate the Optical Density to the value requested by the
customer. Increase the Gain value if the density is too high. To maintain mAs require-
ments (40 - 80 mAs), it may be necessary to increase or decrease the amount of BR-12 or
PMMA used.
9. Make another exposure, develop the film, then measure the Optical Density.
10. Repeat Steps 8 and 9 as necessary, to obtain the mean OD requirement (±0.15 OD).
11. Replace the 3.0 cm absorber with the 6.0 cm absorber. Using the same techniques as in
Steps 8 and 9, make an exposure, develop the film, then measure the Optical Density.
12. Make Offset adjustments to calibrate the Optical Density to the value requested by the
customer. Increase the Offset value if the density is too high. To maintain mAs require-
ments (240 - 350 mAs), it may be necessary to increase or decrease the amount of BR-12
or PMMA used.
13. Make another exposure, develop the film, then measure the Optical Density.
14. Repeat Steps 12 and 13 as necessary, to obtain the mean OD requirement (±0.15 OD).
15. Replace the 6.0 cm absorber with the 3.0 cm absorber, make an exposure, develop the
film, then measure the Optical Density. Ensure the Optical Density reading is within
±0.15 OD of the exposure at 6.0 cm. If necessary, repeat the entire procedure to bring
both the 3.0 cm and the 6.0 cm exposures within the specified requirements.
16. Change the Gain, Offset and M-Density (if required) values for each of the remaining
large focal kV stations to the Gain, Offset, and M-Density values obtained in this proce-
dure.
5.4 kV Tracking—Large Focal Spot (Mo)
This procedure ensures that the automatic exposure control system will produce proper OD
films at intermediate kV levels, large focus, with 5.0 cm of attenuation.
1. Place calibration phantom material (typically 4.0 or 5.0 cm) on the loaded Bucky device
- centered laterally - positioned 1.0 cm over the chest wall edge.
2. Set the unit for an Auto-Time exposure, Large focal, Mo filter. Note that while in Calibra-
tion Screen #2, the exposure mode is automatically set to Auto-Time.
3. Make exposures at 25 kV, 27 kV, 28 kV, 29 kV and 30 kV. Check the optical density
tracking each film.