LORAD AFFINITY Series, Руководство по обслуживанию

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4-20 P/N 9-500-0255
Service Manual
Chapter 4: Calibrations and Performance Checks
Automatic Exposure Control System Calibration
4. If necessary, adjust Gain and Offset at each kV station to maintain OD within ±0.15
O.D. of the Mean Value (Initial Calibration - Large Focus).
Note… When calibrating with high-speed contrast film, each kV station will need
verification and input of the Gain, Offset, and AEC Density.
5.5 Initial Calibration—Large Focal Spot (Rh)
This procedure will make Gain and Offset adjustments to the automatic exposure control
system for large focal spot exposures. Exposures used to adjust the Offset must be taken
between 240 mAs and 350 mAs, and exposures used to adjust the Gain must be taken
between 40 and 80 mAs. Always take sample exposures, then adjust the amount of
attenuation to achieve the proper mAs before making Gain or Offset adjustments.
1. Go to Step 3 for units with no HTC Bucky, units with HTC Bucky, go to Step 2.
Note… For large focal spot calibration with an HTC Bucky, the unit must be in 100
mA mode. Ensure the HTC Threshold is low enough to remain in this mode.
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 28 kV, Large focal spot, Rh filter. Set the Film
data field to the screen-film combination loaded in the cassette.
6. Place 3.5 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. Decrease 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 3.5 cm absorber with the 7.0 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. Decrease 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 7.0 cm absorber with the 3.5 cm absorber, make an exposure, develop the
film, then measure the Optical Density. Ensure the Optical Density reading is within