CPI CMP 200 Series Service Manual page 226

CPI Canada Inc.
3D.6.0 AEC CALIBRATION (WALL BUCKY) Cont
NOTE: BREAKPOINT CALIBRATIONS MAY PREVIOUSLY HAVE BEEN DONE FOR ALL THREE FILM SCREEN COMBINATIONS DURING
TABLE BUCKY AEC CALIBRATION. IF SO, THE REMAINING IMAGE RECEPTORS MUST USE THE CALIBRATION CURVES
PREVIOUSLY ESTABLISHED FOR THOSE FILM SCREENS.
IF A SPARE FILM SCREEN COMBINATION IS AVAILABLE FOR WALL BUCKY USE, IT IS SUGGESTED THAT TWO RECEPTOR
SELECTOR BUTTONS ON THE CONSOLE BE ASSIGNED TO SELECT THE WALL BUCKY. THE FIRST WALL BUCKY SELECTOR
SHOULD BE USED FOR 40 IN. (100 CM) SID'S WITH THE APPROPRIATE PREVIOUSLY CALIBRATED FILM SCREEN. THE SECOND
WALL BUCKY SELECTOR SHOULD THEN BE USED WITH THE SPARE FILM SCREEN AT 72 IN. (180 CM) SID'S.
THIS METHOD WILL ALLOW THE GRID TO BE OPTIMIZED FOR EACH SID, AS A SEPARATE DEDICATED FILM SCREEN WITH ITS
OWN CALIBRATION CURVE CAN BE ASSIGNED TO THE 72 IN. (180CM) SID.
Use these steps to perform the wall Bucky AEC calibration.
Step
Steps 1 to 15 apply only if using one receptor select button for both SID's, using previously calibrated film screens.
1. Set up the X-ray tube stand as shown in figure 3D-8.
2. Align the tube stand and wall Bucky such that the central ray is centered relative to the image receptor.
3. Open up the collimator to expose all three fields of the AEC pickup. Ensure that the central ray remains centered relative to the
image receptor.
4. Place the absorber (with thickness selected for 75 kV per table 3D-8) in the X-ray field, ensuring that the radiation is
COMPLETELY blocked by the absorber.
5. Select the wall Bucky image receptor.
6. Select the slowest film screen used for the wall Bucky, then select the appropriate mA for that film screen per table 3D-8 (example
320 mA for 100 speed film). Select 75 kV, large focus, center field.
7. Make an exposure and note the mAs.
8. Referring to table 3D-9, note the previously established mAs at the 75 kV breakpoint for the film speed being calibrated.
9. Adjust the gain potentiometer on the AEC board for the channel that is connected to the wall Bucky while taking exposures until the
mAs noted in the previous step is obtained.
DO NOT READJUST THE GAIN POT FOR ANY PREVIOUSLY CALIBRATED CHANNELS.
10. Load the test cassette with fresh film and install it in the image receptor. Using the same technique as in the previous step, expose
the film and develop it.
11. Measure the O.D. The desired value should have been previously recorded in a copy of table 3D-11.
Use and disclosure is subject to the restrictions on the title page of this CPI document.
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CMP 200 Service Manual Ch # 901476-05 Rev. A
Action
3D
AEC Calibration
Page 3D-33