Operation Manual
VacuDAP 2002
2002BA01e.DOC / 22.07.2004
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of
22
When doing this, the following requirements should be met:
•
Adjust the field size of the useful beam at a suitable focal distance (e.g. X-ray table) to
approx. 10 cm x 10 cm.
•
Expose the X-ray film (without a supporting foil, where possible) to the radiation at this
focal distance (high contrast, optical density
≤
0.5).
•
Measure the dose (air kerma,
'
K
) in the centre of this field at an uncertainty of
≤
5%
(keep the influence of back scattering as low as possible).
•
Set the X-ray equipment to 70 kV; (20-100) mA.
•
Make the test with the VacuDAP 2002 measuring system completely installed.
If measurements are made both with and without an absorber (see
2.7,
Factory calibration
), the test and, where necessary, re-calibration
must be made separately for the two calibration factors.
Provided the above requirements are satisfied, the following test procedure can be applied:
1. Measure the room temperature
T
and the atmospheric pressure
p
.
2. Find the correction factor for the air density
)
,
(
p
T
f
k
=
ρ
(see data sheet).
3. Expose and process the X-ray film, and accurately measure the field edge lengths
2
1
;
l
l
.
4. Measure the dose
'
K
in the same plane as in the previous exposure of the film, and
simultaneously determine the dose area product
A
K
⋅
using the installed VacuDAP 2002
measuring system.
5. Calculate the reference value for the dose area product
'
'
A
K
⋅
from:
2
1
'
'
'
l
l
K
A
K
⋅
⋅
=
⋅
;
where
'
K
....
...dose (air kerma) in mGy
2
1
;
l
l
….edge length of exposed area in cm
6. Determine the deviation,
F
, of the indicated value
A
K
⋅
from the reference value
'
'
A
K
⋅
:
'
'
)
(
A
K
A
K
k
F
⋅
⋅
=
ρ
ρ
k
........correction factor (see data sheet)
If the deviation does not exceed ±10%, i.e.:
1
.
1
9
.
0
≤
≤
F
, a re-calibration is not necessary.
If the deviation is greater, calculate the new calibration factor,
CF_ABOVE
new
(or
CF_UNDER
new
) as
follows:
F
old
new
CF_ABOVE
CF_ABOVE
=
The old calibration factor
CF_ABOVE
old
(or
CF_UNDER
old
) can be read from the display, when the
display unit is in the parameter changing menue (
SETTINGS
, see 3.3.9,
Changing of parameters
) at
the appropriate step (
CALIB
,
CF_ABOVE
, see fig. 5,
Changing settings
). If necessary, the new
calibration factor can be entered there as well.
After the calibration factor has been changed, the calibration must be re-
checked.
