3.0 Precalibration Notes; 4.0 Absorber Equivalents - CPI Indico 100 Series Service And Installation Manual

3D
AEC Calibration
3D.3.0 PRECALIBRATION NOTES:
This section contains information that must be understood and confirmed prior to and/or during AEC
calibration.
CAUTION: THE PROCEDURES IN THESE SECTIONS REQUIRE X-RAY EXPOSURES. TAKE ALL
SAFETY PRECAUTIONS TO PROTECT PERSONNEL FROM X-RADIATION.
SHOULD AN IMPROPER TECHNIQUE BE SELECTED, OR AN AEC FAULT OCCUR CAUSING NO AEC
FEEDBACK SIGNAL TO THE GENERATOR, THE EXPOSURE WILL TERMINATE IF THE RAMP
VOLTAGE FAILS TO REACH 4% OF THE EXPECTED RAMP VOLTAGE WHEN THE EXPOSURE TIME
REACHES 20% OF THE SELECTED B.U.T. (B.U.T. = BACK UP TIME).
•
When using PMTs or photo diodes for AEC from the output of an image intensifier, there is normally
no need to iterate all the kV break points. It is usually sufficient to use the 75 kV breakpoint
calibration value for that film screen at all kV breakpoints. If doing this, the calibration values should
be confirmed using the acquired digital images at all kV breakpoints.
•
During calibration, all AEC exposures should be done using mA values such that the exposures are
in the 30 to 100 ms range UNLESS STATED OTHERWISE.
•
During AEC calibration, always ensure that the central ray is centered relative to the image receptor.
•
Prior to placing the absorbers, ensure that the collimator is opened sufficiently to cover ALL fields on
the AEC pickup device.
•
Ensure that the absorber is positioned such as to fully cover the X-ray field. The absorber must
extend a minimum of 3/8" (10 mm) beyond the X-ray field.
•
All components/assemblies used during AEC calibration must be those which will be used during
procedures, and must be positioned as they will be in actual use of the X-ray room.
•
The generator must be known to be calibrated before proceeding.
•
During AEC calibration, if exposure times do not change if the mA is varied, it may be that the input
signal level to the AEC board may be too high. If this is experienced, check the ramp voltage at the
output of the first gain stage (the first operational amplifier output) on the AEC board for the subject
AEC channel. This voltage must never exceed 10 V. If this voltage does exceed 10 V, reduce the
input signal level as required.
3D.4.0 ABSORBER EQUIVALENTS
The following calibration procedure details the use of copper absorbers. Water or aluminum may be used as
an absorber instead of copper if required. Table 3E-1 in chapter 3E (ABS calibration) lists water and
aluminum equivalents of selected copper thickness.
Page 3D-22 Rev. D Millenia / Indico 100 Series Service Manual
CPI Canada Inc.
Ch # 740904-06