1.3 Aec Limitations: Maximum Exposure Times - CPI Indico 100 Series Service And Installation Manual

3D
AEC Calibration
3D.1.3 AEC Limitations: Maximum Exposure Times
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.
RLF (reciprocity law failure) compensation is provided to compensate for longer AEC exposure
times. An offset may be added to each AEC calibration set (each film screen combination) to increase the
AEC ON time as exposure time increases. RLF compensation is applied to the following range of times:
•
50 ms to 500 ms
•
500 ms to 1000 ms
•
1000 ms and above.
Care must be exercised when using table buckys with low kV values because most table tops and grids
absorb considerable radiation in the range of 60 - 65 kVp. This will adversely affect AEC operation.
Figure 3D-2 shows the effect of kVp, optical density, and radiation. Note particularly the nonlinear change in
density at 85-90 kVp.
Page 3D-4
Figure 3D-2: kVp vs optical density vs dose
Rev. D Millenia / Indico 100 Series Service Manual
CPI Canada Inc.
Ch # 740904-06