Chapter 4 Theory of Operation
Revision W HF Series X-ray Generators - Service Manual
4-18 Quantum Medical Imaging
The board is divided into three major functions described in the following
paragraphs:
• +300 VDC power supply
• AEC Control Circuit
• Tomography Interface Circuit
+300 VDC Power Supply
The universal board has an adjustable +300 VDC power supply for ion cham-
bers that require +300 VDC for the detector operation (e.g., Siemens ion
chamber). The power supply is a DC-to-DC converter that converts +50 VDC
(input through A11J1) to +300 VDC. The power supply is regulated with
closed-loop circuitry. A11R10 adjusts the power supply output on connector
A11TB1. The power supply has a thermal fuse (A11F1) and current limit pro-
tection against short circuits (A11U1).
AEC Control Circuitry
The AEC control circuitry can accept one out of two ion chamber inputs
(either wall or table) based on selection from the OCP. (In the future, four
inputs will be available.) The ion chambers input connectors are 9-pin D-type
connectors, configured as follows:
• A11J10 - Table ion chamber, selected from the OCP as TABLE receptor.
• A11J8 - Wall #1 ion chamber, selected from the OCP as WALL receptor.
• A11J12 - Currently not available for use.
• A11J13 - Currently not available for use.
Different types of ion chamber can be connected to each input. Each ion
chamber is configured independently using the Ion Chamber Configuration
menu to set the characteristics of the ion chamber. These settings enable the
AEC Control circuitry on the Universal Board to generate the appropriate sig-
nal. The information is sent via serial communication from the OCP Control
Board to the Logic board, then to the Universal AEC Board. The selected ion
chamber outputs a signal that is processed by the AEC Control circuit and is
sent to the KVP Control Board. The KVP Control Board compares the pro-
cessed signal with a reference voltage. When the processed signal is equal to
the reference voltage, the exposure is terminated.
The AEC Control circuitry requires adjustment using potentiometers. The
potentiometers are adjusted during AEC calibration based on the ion chamber
type and film/screen combination. The circuits are divided into two sections:
one for a level type ion chamber, and one for a slope type ion chamber.
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