LORAD AFFINITY Series, Service Manual

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P/N 9-500-0255 5-7
Service Manual
Chapter 5: Maintenance—General
Troubleshooting
Auto-kV—SRL 2000 Bucky Operation
When this mode, along with the Molybdenum filter, is selected, the kV will be the
default kV selected in the exposure defaults screen. The starting kV may be changed
to 25 kV or 26 kV. When the Rhodium filter is selected, the kV defaults to 28 kV.
Upon exposure initiation, the AEC signal is sampled and the kV may be incremented
upward to a maximum value of 30 kV if the Molybdenum filter is selected, or 32 kV
if the Rhodium filter is selected. The exposure is terminated at a mAs value near one
of the selected mAs windows (125 mAs, 165 mAs, 200 mAs, or the AUTOmatic 200
mrad window). The final kV and post-mAs is displayed upon termination of the
exposure.
Auto-kV—HTC Bucky Operation
When this mode and the Molybdenum filter are selected, the kV defaults to a value
determined by the Compression Height Threshold setting. The kV defaults to 24 kV
for a compression height value less than the threshold, or to 25 kV for compression
height values above the threshold. When the Rhodium filter is selected, the kV
defaults to 28 kV. The exposure is terminated at a mAs value near the selected mAs
windows (125 mAs, 165 mAs, 200 mAs, or the AUTOmatic 200 mrad window),
selectable by the operator. The final kV and post mAs are displayed upon
termination of the exposure.
Auto-Filter
This mode provides full automatic operation of all technique factors. Upon exposure
initiation, the AEC signal is sampled to determine if the kV needs to be incremented
upward to provide an exposure within the 200 mAs window, or the 200 mrad
window. When determined by the AutoFILTER algorithm, the exposure is
momentarily interrupted and the Rhodium filter is moved into the beam in place of
the Molybdenum filter. After the kV or kV/filter has been selected by the algorithm,
the Auto-Time function completes the exposure. The final kV, post-mAs, and Filter
are displayed upon termination of the exposure.
3.1.8 Automatic Exposure Control
A three cell solid-state detector and pre-amplifier are located in the image receptor
support device. It is manually positioned to one of 7 positions by the technologist,
depending on the anatomy of the breast under examination. It is ideally placed
under the glandular, or most dense, area of the breast. The signal from the detector
represents the average attenuation of the area under the three cells and is sent to the
microprocessor. It is first converted into a digital signal and used as a variable in an
algorithm that predicts the time required to obtain a standard (calibrated) optical
density. This signal is also used in Auto-kV and Auto-Filter modes to determine the
kV and filter (Mo or Rh) for completing the exposure within a predetermined time
window.
There are two safety back-up-timers, firmware and hardware, utilized to terminate
the exposure should there be failure of system components or firmware corruption.