P/N 9-500-0255 4-25
Service Manual
Chapter 4: Calibrations and Performance Checks
Automatic Exposure Control System Calibration
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).
4. 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 (6 - 14 mAs), it may be necessary to increase or decrease the amount of BR-12 or
PMMA used.
5. Make another exposure, develop the film, then measure the Optical Density.
6. Repeat Steps 4 and 5 as necessary, to obtain the mean OD requirement (±0.15 OD).
7. Replace the 2.5 cm absorber with the 6.0 cm absorber. Using the same techniques as in
Steps 5 and 6, make an exposure, develop the film, then measure the Optical Density.
8. 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 (65 - 130 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 6.0 cm absorber with the 2.5 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 2.5 cm and the 6.0 cm exposures within the specified requirements.
12. Change the Gain, Offset and M-Density (if required) values for each of the remaining
small focal spot kV stations to the Gain, Offset, and M-Density values obtained in this
procedure.
5.13 Starting AEC Values - Small Focal Spot
This procedure inputs recommended starting AEC values for 22 through 24 kV, and for 31
through 39 kV for the Small focus.
1. Input the values for Gain, Offset and AEC Density used at 25 kV into the corresponding
fields for 20 through 24 kV for Mo.
2. Input the values for Gain, Offset and AEC Density used at 30 kV into the corresponding
fields for 31 through 35 kV for Mo.
3. Select the Rhodium (Rh) filter. Input the values for Gain, Offset, and M-Density used at
32 kV into the corresponding fields for 33 through 39 kV for Rh.
4. Re-select the Molybdenum filter.
5.14 Performance Test - Small Spot (Mo)
This procedure ensures that the AEC system consistently produces films at the required
optical density (within 0.15 OD) using the Mo filter.
1. Make a small focal spot exposure using the phantom thicknesses and kV combinations
shown in the worksheet at the end of this procedure (refer to Table 4-8: AEC Perfor-
mance Worksheet—Small Focal Spot, Mo Filter). In the space provided, record the mAs
and optical density values.
2. Verify that the maximum optical density deviation on each film does not exceed ±0.15
OD. If it does, repeat the Gain and Offset adjustments for the kV’s that are out of toler-
ance.
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