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CPI Canada Inc.
AEC Calibration
3D
Millenia / Indico 100 Series Service Manual Ch # 740904-06 Rev. D
Page 3D-3
3D.1.2 AEC
Limitations:
Minimum
Response
Time
The X-ray generator (including the AEC pickup chamber) has a minimum response time from start of the
exposure command to a kV value sufficient to start X-rays. There is a further delay to the start of current flow
from the AEC device. Likewise, there is a minimum response time from when the AEC stop command is
issued to when the kV has actually decreased to the point that X-rays are no longer produced. Figure 3D-1
depicts this graphically.
Figure 3D-1: Relative timing of AEC ramp vs exposure command and kVp
•
1 to 2 is the time from the exposure start command to kVp start.
Time = 1 to 3 ms.
•
2 to 3 is the reaction time of the solid state/ion chamber to start a current flow.
Time = 1 to 3 ms.
•
3 to 4 is the required exposure time.
•
4 is the AEC stop command from the generator AEC circuits.
•
4 to 5 is the generator shut down time including cable discharge time etc.
Time = 1.5 to 3.0 ms.
•
1 to 6 is the total time the exposure switch is activated.
•
FOR AEC BOARDS WITH SHORT AEC TIME COMPENSATION (FIGURE 3D-9 AND 3D-11) AEC
TECHNIQUES SHOULD HAVE MINIMUM EXPOSURE TIMES GREATER THAN 5 MS. FOR ALL
OTHER AEC BOARDS MINIMUM EXPOSURE TIMES SHOULD BE GREATER THAN 15 MS.