Quantum ODYSSEY HF Series, Service Manual

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Chapter 4 Theory of Operation
Revision W HF Series X-ray Generators - Service Manual
4-8
Quantum Medical Imaging
Cathode Amplifiers are compared with the KV PROGRAM (from voltage at Com-
parators U1C, U2C) and are also sent to the Logic Circuit via Parallel to Serial A/D
U13. Comparator U1C's output varies the output frequency of Pulse-Width Modu-
lator U3, depending on the desired kVp voltage. The output of Pulse-Width Mod-
ulator U3 is sent to the anode IGBT Driver Board (part of Power Module
Assembly). This board drives the IGBT's, which in turn drive the H.V. Trans-
former, thus producing the high voltage for the x-ray tube. The cathode Amplifi-
ers (U2A, U2B), Comparators (U1C U2C) and Pulse-Width Modulator U4 work in a
similar manner. In lower-power systems, Pulse-Width Modulator U4 is not used,
and the outputs of Amplifiers U1B and U2B are summed together to control U4.
Comparators (U6A, U6B), Amplifiers (U1D, U2D) and Comparator U6C monitor
the high voltage to check for an over-voltage condition. A watchdog timer (Re-
triggerable One-Shot U7A) must be triggered every 50 msec. by the TRIGGER
input from the Logic Circuit (via Address Decoder U15) in order for an x-ray to
occur. If this pulse stream were missing, it would signal a failure condition thus
terminating the x-ray and the ERROR signal is output through D-Flip-Flop U12A
and Logic Inverter U21A to the Logic Circuit. The 7 TRIGGER signal from the
Logic Circuit (generated at the beginning of exposure cycle) is applied to 7-Sec-
ond One-Shot U7B, which produces a seven-second positive-going pulse. If the
exposure is not terminated within seven seconds, D-Flip-Flop U12A and Logic
Inverter U21A generate the ERROR signal.
Amplifiers (U10A, U10B), Amplifiers (U10C, U10D) and Driver Q3 monitor the x-
ray tube current via an mA sense resistor in the High Voltage Tank and compare
this value to the mA Program and Filament Program values (received from the
Logic Circuit via Serial to Parallel D/A U16. The FIL CURRENT output from this
circuit is a voltage that is sent to the Filament Control Regulator Circuit to vary
the filament voltage based on the selected x-ray tube current.
Address Decoder U15, Parallel to Serial A/D U13, and Serial to Parallel D/A U16
enable communication between the Logic Circuit and the KVP & Filament Control
Circuit. Parallel to Serial A/D U13 converts analog signals from the KVP & Fila-
ment Control Circuit to digital signals for input to the Logic Circuit. Serial to Par-
allel D/A U16 converts digital signals from the Logic Circuit to analog signals for
use by the KVP & Filament Control Circuit.
LINE MONITOR CIRCUIT (NON-SE SINGLE-PHASE AND THREE-PHASE SYSTEMS)
The Line Monitor Circuit consists of three circuits: an input line monitor circuit, a
circuit that bleeds off the high voltage from the IGBT capacitor banks and an
auto-shutoff circuit that turns off the generator after 1 hour of inactivity. The
auto-shutoff circuit also allows the microprocessor to turn off the generator in the
event a fault occurs in the system. The operation of the Line Monitor Circuit is as
follows:
Input Line Monitor Circuit
The Input Line Monitor Circuit monitors the incoming line voltage to ensure it
is at the correct voltage level required for taking an exposure. This circuit is
configurable for either single-phase systems (anode capacitor bank only) or