Del Medical EPEX Omniflex IV, Service Manual

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EPEX/Omniflex IV System Service Manual
4-42 Adjustments and Calibration
Adjusting Automatic Exposure Control (AEC)
Introduction
This topic covers interfacing and calibration of the AEC.
AEC Limitations: Minimum Response Time
The X-ray Generator (including the AEC pickup chamber) has a minimum
response time from the start of the exposure command until there is a kV
value sufficient to start producing X-rays. There is a further delay before
the start of current flows from the AEC device. Likewise, there is a
minimum response time from when the AEC stop command is issued until
the kV has actually decreased to the point that X-rays are no longer
produced. The following illustration depicts this graphically.
Figure 4-8.
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 DirectRay Detector 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
and so on. 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, AEC techniques
should have minimum exposure times greater than 5 ms.