PTW NORMI 13, Руководство пользователя

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NORMI 13 (T42023)
Operating Manual - Constancy Test
D703.131.00/03 en 23
3.4.3 Optical Density
For both, automatic exposure control and man-
ual exposure setting, the measured optical den-
sity shall not deviate more than ±30% from the
reference value.
3.4.4 Luminance
For both, automatic exposure control and man-
ual exposure setting, the maximum deviation ΔL
of the measured luminance shall not exceed
+100% / -50%.
3.4.5 Pixel Value
Perform three ROI measurements for determining
the permitted deviations from the reference value:
– at the reference step (field in the middle, mea-
sured behind 1 mm of copper) P
reference
– at the adjoining step (measured behind
0.65 mm of copper) P
dose+step
– at the adjoining step (measured behind
1.4 mm of copper) P
dose+step
Calculate the maximum (P
+1
) and the minimum
(P
-1
) deviation from the reference value according
to the following formula:
– P
+1
= P
reference
+ factor × (P
dose+step
-P
reference
)
– P
-1
= P
reference
+ factor × (P
dose+step
-P
reference
)
The factor used in the calculation depends on the
voltage, it is 0.45 for 70 kV and 0.7 for 100 kV (see
Table 1 ).
70 kV 100 kV
Limit of the pixel value towards a
lower dose: P
-1
P
1
+ 0.45 × (P
1.4
- P
1
) P
1
+ 0.7× (P
1.4
- P
1
)
Limit of the pixel value towards a
higher dose: P
+1
P
1
+ 0.45 × (P
0.65
- P
1
) P
1
+ 0.7× (P
0.65
- P
1
)
P
1
= pixel value behind the 1-mm Cu step (reference value)
P
0.65
= pixel value behind the 0.65-mm Cu step
P
1.4
= pixel value behind the 1.4-mm Cu step
Table 1: Formulas for calculation of the permitted deviations