Composition and Operation Principle
3-3
d) Principle of Tube Current Loop Control
In the exposure process, signals sampled by the current sampling circuit are sent to the
SYS board, by which a comparison is carried out between feedback signals and internal
reference signals. After the operation, a proper filament heating current reference value is
added to the filament heating module, which sends the corresponding current to the X-ray
tube filament based on the reference value, resulting in a stable tube current.
e) Principle of Capacity Limit kV, mA and mAs Chain Protection
The capacity limits kV, mA and mAs chain protection is controlled by the operation of a
microprocessor. The current exposure parameters are tested by the main unit in real-time,
so as to limit the exposure parameters over capacity range. For example, when kV goes
up to a certain value, the maximum output upper limits of mA and mAs are limited and
lowered automatically.
f) Principle of Imaging Time Control
The imaging time control circuit is controlled by a microprocessor. In the process of
exposure, the tube current is integrated by the microprocessor, and the exposure stops
when the integral value reaches the preset mAs. Meanwhile, to interrupt manually, just
release the hand switch before the exposure time ends.
g) Principle of General Imaging Control
In the state of imaging, choose parameters such as kV and mAs on the panel according to
the shooting conditions. When using the hand switch, press Level 1 of the hand switch, or
use the remote control to press "A" and "B" keys, the SYS board CPU detects the
message and sends a command, and the filament heating circuit will quickly heat up the
cathode filament of the X-ray tube. When using the hand switch, press Level 2 of hand
switch, or do nothing with the remote control, the SYS board sends the exposure
command, the PWM (pulse width modulation) circuit of the PWM drive module will
generate modulating signals to drive the inverter of the generator to operate. The inverter
drives the high voltage transform device to generate high voltage to load to the X-ray tube
that is to generate X-ray and achieve the imaging function. If the hand switch is released
during the exposure, the exposure imaging will stop immediately.
h) Principle of Failure Detection
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