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7
FILTRATION CORRECTION (kVp Measurement)
The Model 810 Meter is calibrated for tungsten tube x-rays with 1.5 mm of Al
filtering. When the x-ray has different filtration, refer to the table below and make
the appropriate correction to the kVp reading.
At 50 mA
Added
Filtration
60 kVp
80 kVp
100 kVp
120 kVp
0.31 mm Al
-0.2
-0.5
-0.5
-0.5
1 mm Al
-1.1
-1.5
-2.6
-3.0
At 100 mA
Added
Filtration
60 kVp
80 kVp
100 kVp
120 kVp
0.31 mm Al
-0.2
-0.6
-0.8
-1.7
1 mm Al
-0.9
-1.7
-1.7
-3.4
For example, if your x-ray has 2.5 mm Al, that is equivalent to 1.0 mm of added
filtration. A reading at approximately 60 kVp, 50 mA will be 1.1 kV high. Subtract
1.1 kVp to get the correct reading.
The values can also be interpolated. For example, when taking a reading at 70
kVp, 100mA with 0.3 mm additional filtration (1.8 mm total), use a correction
factor mid way between -0.2 and -0.6, which is -0.4. Therefore, when taking a
measurement at about 70 kVp, 100 mA with 1.8 mm of Al filtration, subtract 0.4
kVp.
For values below about 50 kVp, the correction factor is minimal and can be
ignored.
CONNECTIONS
No external connections are made to the instrument.