LORAD AFFINITY Series, Service Manual

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P/N 9-500-0255 4-21
Service Manual
Chapter 4: Calibrations and Performance Checks
Automatic Exposure Control System Calibration
±0.15 OD of the exposure at 7.0 cm. If necessary, repeat the entire procedure to bring
both the 3.5 cm and the 7.0 cm exposures within the specified requirements.
16. Change the Gain, Offset and M-Density (if required) values for each of the remaining
large focus kV stations to the Gain, Offset, and M-Density values obtained in this proce-
dure.
5.6 kV Tracking—Large Focal Spot (Rh)
This procedure ensures that the automatic exposure control system will produce proper OD
films at intermediate kV levels, large focal spot, with 5.0 cm of attenuation.
1. Place calibration phantom material (typically 5.0 to 6.0 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, Rh filter. Note that while in Calibra-
tion Screen #2, the exposure mode is automatically set to Auto-Time.
3. Make exposures at 29 kV, 30 kV, 31 kV, and 32 kV. Check the optical density tracking
each film.
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.
5.7 Starting AEC Values—Large Focal Spot
This procedure inputs recommended starting AEC values for 20 - 24 kV, and for 31 - 39 kV
for the Large focus.
1. Input the values for Gain, Offset and AEC Density used at 25 kV into the corresponding
fields for 20 through 24 kV.
2. Input the values for Gain, Offset and AEC Density used at 30 kV into the corresponding
fields for 31 through 35 kV.
3. Select the Rhodium (Rh) filter. Input the values for Gain, Offset, and AEC Density used at
32 kV for each corresponding value at 33 through 39 kV.
4. Re-select the Molybdenum filter.
5.8 Performance Test—Large Focal Spot (Mo)
This procedure ensures that the AEC system consistently produces films at the required
optical density (+0.15 OD) using the Mo filter.
1. Make an exposure using the phantom thicknesses and kV combinations shown in the
worksheet at the end of this procedure (refer to Table 4-6: AEC Performance Work-
sheet—Large 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.
Note… Do not readjust Gain or Offset at 26 kV (initial calibration).