HF Series Generators
Calibration
CA-1036R2
49
2.8 ABC CALIBRATION
The purpose of the ABC System is to maintain an optimum constant Image
Tube Output Brightness by controlling the X-ray kV during Fluoro exams,
regardless of changes in the patient opacity viewed on the TV monitor.
The closed-loop ABC System can monitor the Image Tube Output Brightness
through two ways: Photomultiplier Tube or TV Camera.
2.8.1 ABC SYSTEM WITH PHOTOMULTIPLIER TUBE
This operation requires the AEC Control Board A3012--x6/x7/x9
(Digital version).
On this system the Photomultiplier current signal, which is proportional to the
Image Tube Output Brightness, is used as brightness signal “PT Input”forthe
ABC circuitry of the Generator. (Refer to Illustration 2-5).
This analogic signal is converted to a voltage signal in the Photomultiplier
Amplifier Board and sent to a peak-detector in the AEC Control Board. The peak
signal obtained is then held through a “Sample and Hold” circuitry after a
synchronism pulse. The peak signal held is adapted to obtain finally the “ABC
IN” signal which is so the Photomultiplier signal-peak held between
synchronism pulses. This signal is then compared to a window reference.
Brightness error at the comparator output is sent as “kV Up” and “kV Down”to
the Generator where is used to drive the Fluoro kV c ontrol. The closed-loop
operation requires more or less brightness thru “kV Up” and “kV Down” demand
signals respectively. Patient Entrance Dose is automatically varied so that
optimum constant Image Tube Output Brightness is maintained.
Note .
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