CPI Indico 100 Series Service And Installation Manual page 176

3D
AEC Calibration
3D.10.0 AEC CALIBRATION (WALL BUCKY) Cont
Step
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
14.
15.
16.
Page 3D-42
USE OF ONE FILM SCREEN FOR BOTH SID'S USING PREVIOUSLY CALIBRATED
Set up the X-ray tube stand as shown in figure 3D-15.
Align the tube stand and wall bucky such that the central ray is centered relative to the
image receptor.
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.
Place the R probe at the film plane, i.e. behind the grid. If this cannot be done, then
attach the probe to the front of the bucky. Ensure that the R-probe is located directly
under the central ray. The R meter must be set to measure in the micro-R range.
Place 1.5 mm of copper (pure grade) in front of the collimator, ensuring that the radiation
is COMPLETELY blocked by the absorber.
Select the wall bucky image receptor.
Select the slowest film screen used for the wall bucky, then select the appropriate mA for
that film screen per table 3D-13 (example 320 mA for 100 speed film). Select 75 kV,
large focus, center field.
Make an exposure and note the dose and mAs.
Referring to table 3D-14, select the previously established dose required at the 75 kV
knee breakpoint for the film speed being calibrated.
Note that the dose values in the table are based on a specific R-probe placement
during table bucky calibration (either at the film plane, or alternately in front of the
bucky). If the probe placement for wall bucky calibration is not the same as it was
for table bucky calibration, use the estimated dose correction factor in this
subsection under GRID ABSORPTION.
Adjust the required gain potentiometer on the AEC board (see note below) while taking
exposures until the dose noted in the previous step is obtained.
•
CHANNEL 2 ON THE AEC BOARD IS TYPICALLY USED FOR THE WALL
BUCKY AEC CHAMBER. YOUR INSTALLATION MAY USE A DIFFERENT
CHANNEL ON THE AEC BOARD. DO NOT READJUST THE GAIN POT FOR
THE CHANNEL THAT WAS PREVIOUSLY CALIBRATED (FOR TABLE BUCKY).
•
REFER TO TABLE 3D-10 FOR THE AEC BOARD GAIN POTENTIOMETER
(GAIN POT) DESIGNATIONS FOR THE VARIOUS AEC BOARDS.
Load the test cassette with fresh film and install it in the image receptor. Using the same
technique, expose the film and develop it.
Measure the O.D. The desired value should have been previously recorded in a copy of
table 3D-1.
If the measured O.D. is not within 5% of the desired value, adjust the gain pot (as per
step 10) to increase or decrease the density, then repeat the previous two steps.
Change the SID to 40" (100 CM) and repeat steps 11 to 13. Adjust the gain pot if
necessary to achieve an acceptable compromise between both SID's.
Verify the O.D. at a range of different kV's.
USE OF TWO FILM SCREENS (ONE FOR EACH SID) USING ONE PREVIOUSLY
CALIBRATED FILM SCREEN AND ONE UNCALIBRATED FILM SCREEN
Select the wall bucky image receptor via the selector configured for the 40" (100 CM)
SID.
Repeat steps 1 to 13 at the 40" (100 CM) SID position using the appropriate previously
calibrated film screen.
Rev. D Millenia / Indico 100 Series Service Manual
Action
FILM SCREENS
CPI Canada Inc.
Ch # 740904-06