3D
AEC Calibration
CPI Canada Inc.
Page 3D-26
Rev. D Millenia / Indico 100 Series Service Manual Ch # 740904-06
3D.5.0 AEC CALIBRATION (TABLE BUCKY) Cont
FILM SPEED
FILM PLANE DOSE @ 75 kV
100 1025
±
25 uR
200 550
±
25 uR
400 260
±
12 uR
800 135
±
12 uR
Table 3D-12: Estimated knee dose vs film speed @ 75 kV
These are TYPICAL dose inputs to the film cassette plane at an SID of 40
″″″″
(100mm), using a grid with
a 12:1 ratio.
NOTE: To convert from
µµµµ
R to
µµµµ
Gy divide the value in
µµµµ
R by 100. This will give the value in
µµµµ
Gy (for example
100
µµµµ
R = 1
µµµµ
Gy.
Step
Action
21.
Load a 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.
22.
Measure the optical density. The desired value should have been previously recorded in
a copy of table 3D-1.
23.
If the measured O.D. is not within 5% of the desired value, adjust the gain pot (as per
step 20) to increase or decrease the density, then repeat the previous two steps.
24.
Once the desired film density is achieved, record the mAs, dose, calibration number and
O.D. in a copy of table 3D-14.
FOR EACH BREAKPOINT IN THE REMAINDER OF THIS SECTION, START WITH THE
SUGGESTED DOSE AS PER TABLE 3D-13. AFTER THAT DOSE IS ACHIEVED, A FILM MUST
BE EXPOSED AND THE O.D. VERIFIED. FURTHER DOSE ITERATIONS MAY BE REQUIRED TO
ACHIEVE THE DESIRED OPTICAL DENSITY.
DO NOT READJUST THE AEC BOARD GAIN POT AFTER THE 75KV KNEE
BREAKPOINT IS CALIBRATED.
DOSE/DENSITY ADJUSTMENTS WILL ONLY BE DONE BY
ADJUSTING THE CALIBRATION VALUES FOR THE OTHER KV BREAKPOINTS.
55 KV BREAKPOINT CALIBRATION:
25.
Replace the 1.5 mm copper absorber previously installed with a 0.5 mm copper sheet.
As before, ensure that the absorber fully blocks the X-ray field.
26.
Select the 55 kV breakpoint.
27.
Make an exposure and note the dose. Use mA values as per table 3D-13.
28.
Adjust the 55 kV calibration numbers using the + or - buttons such that the actual dose
is equal to the target dose at 55 kV for the selected film speed per table 3D-13.
DO NOT READJUST THE AEC BOARD GAIN POT.