Fluke Biomedical 10100AT - Manual (Page 73)

Appendix
Calibration and Verification
C
C-5
PTB traceable: PTB traceable reference chambers are accurate to within ± 1.5% at each beam quality.
Matching between the reference and unknown chamber is accurate to ± 1%. Thus, PTB traceable
calibrations are accurate to within ± 2.5%.
Calibration Verification
NIST traceable: For NIST traceable calibrations, a chamber will be reported to be outside of its
calibration accuracy specification when a new calibration value differs from the old calibration value by
more than ± 4%. This includes the ± 2% accuracy specification plus ± 1% for the verification reference
plus ± 1% for the verification match.
PTB traceable: For PTB traceable calibrations, a chamber will be reported to be outside of its
calibration accuracy specification when a new calibration value differs from the old calibration value by
more than ± 5%. This includes the ± 2.5% accuracy specification plus ± 1.5% for the verification
reference plus ± 1% for the verification match.
C.6 Energy Correction Factors
C.6.1 Diagnostic - Unattenuated Beam (In front of the phantom)
The energy correction factors for the 96035B are determined for the unattenuated diagnostic beam using
the PTB defined DV series of beam qualities given below in Table C-1.
Table C-1. Specifications for PTB Defined Unattenuated Beam Qualities
PTB Denomination kVp
Added Filtration
in mm Al
First HVL
in mm Al
First HVL
in mm Cu
DV30 30 2.5 1.05 0.031
DV40 40 2.5 1.42 0.045
DV50 50 2.5 1.82 0.059
DV70 70 2.5 2.45 0.081
DV90 90 2.5 3.10 0.112
DV100 100 2.5 3.60 0.126
DV120 120 2.5 4.30 0.165
DV150 150 2.5 5.40 0.231
Typical energy correction factor curves are obtained by dividing the calibration factor at each beam
quality by the calibration factor at a reference point and plotting the result versus first HVL. L100 is
chosen as the reference point for chambers receiving the standard calibration while DV70 is chosen for
chambers receiving the PTB calibration option.
The energy correction factors are multiplicative, such that multiplying the measured ion chamber output at
any beam quality by the appropriate value from the curve will correct readings not made at the calibration
factor beam quality.
The typical correction factor curves for the unattenuated beam are shown below normalized to L100 in
Figure C-3 and DV70 in Figure C-4. All 96035B ion chambers must have an actual correction factor
within ± 1.5% of the value shown in the curves at any point.
The numerical value shown beside each point is the kVp value of that point in the DV series of beam
qualities. Users making measurements in an unattenuated beam may use these values to easily obtain
the appropriate correction factor. For a more precise correction factor value, the user may calculate the
actual first HVL and locate the proper correction value on the curve.