CPI CMP 200 Series Service Manual page 228

CPI Canada Inc.
3D.8.0 AEC OVERVIEW AND BACKGROUND INFORMATION
AEC exposures should normally be kept well under one second. When X-ray techniques are used that result
in longer exposures, the film density will not be correct due to failure of reciprocity of the film.
Care must be exercised when using low kV values with table Buckys because most tabletops and grids
absorb considerable radiation in the range of 60 – 65 kV. This will adversely affect AEC operation.
3D.8.1 Film/Screen Response vs. kV
Film screen response to kV is not linear. Therefore, compensation must be provided in order to maintain
constant film density as kV is changed for different anatomical studies. By selecting and calibrating various
kV breakpoints, the overall system response will be compensated such as to yield a constant film density.
Up to eight breakpoints per film screen combination are available. The eight breakpoints are spread
over three kV ranges as shown below:
•
Low kV:
•
Knee kV:
•
High kV:
Refer to figure 3D-9.
Use and disclosure is subject to the restrictions on the title page of this CPI document.
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CMP 200 Service Manual
50, 55, 65 kV.
75 kV.
85, 95, 110, 130 kV.
Figure 3D-9: kV vs. relative density
Ch # 901476-05 Rev. A
3D
AEC Calibration
Page 3D-35