QDR
4500 Technical Manual
4-28
DO NOT ADJUST THE A/D GAIN UNLESS ABSOLUTELY NECESSARY. Any
adjustment of this potentiometer affects the QC highs and lows.
If an adjustment is required, proceed as follows:
The object is to have all the detectors fall within the 4.5V and 8.5V range, so first adjust the
average signal level to approximately 6.25V, then check to see if all the detectors are now
within the 4.5V and 8.5V range. If they are, the adjustment is complete. If they are not,
adjust the gain (in the required direction) until all the detectors are within the 4.5V and 8.5V
range.
BEAM FLATTENING
WARNING:
X-rays are being generated during this procedure. Keep hands, head and other
body parts out of beam.
This procedure flattens the X-ray beam for each scan mode.
Note:
All covers, table mat, etc., normally in the X-ray path, must be on the Scanner before
running beam flattening.
1.
From DOS type BIGFLAT. This move the table and arm to the correct position and
turns on the laser.
2.
Place the phantom on end (vertical) with the laser 1.5” in from the left end and centered
(some phantoms will have a target hole, if not, use a ruler).
3.
Press <Esc> <Esc>.
4.
Go to survey program SUSQ located in the MENU directory.
5.
Set Pulse 1.
6.
Set Gains 2, 1.
7.
Set Mode 3.
8.
Set Aperture to 7 (this step for QDR 4500A and SL only).
9.
Bring up graphic display. CTRL PGDN
10.
Turn on X-rays and observe the screen.
11.
Check that phantom covers the whole beam. This is critical. If phantom does not cover
the whole beam, move it until it does. Keep the phantom as straight as possible.
12.
Turn off X-rays. Exit to the DOS prompt.
13.
From the DOS prompt type BIGFLAT. A scan that moves the beam off the phantom
then onto the “tissue” part of the phantom, is performed for each mode. This takes about
30 minutes.
14.
When flattening is complete, run a QC scan and ignore it.
15.
Using the phantom, run an AP/Lateral pair.
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