Fluke Biomedical 07-479 - Manual (Page 10)

Victoreen 07-479
Operators Manual
3-2
3.3 Determining mAs Requirements
The values in Table 3-1 are intended to guide the user in selecting the mAs required for a particular kVp
measurement. Any mAs beyond the user-designated amount will not be included in the measurement.
(Refer to Section 2 - Theory of Operation for a detailed discussion.)
The values in Table 3-1 are derived from single-
phase measurements. Three phase machines will
generally require 70% of the mAs determined from
the table.
mAs requirements may vary considerably depending on the following conditions:
1. Detector sensitivity
2. Tube filtration
3. Radiation Waveform
4. FDD
5. mAs errors in the x-ray machine
If this technique fails to produce a result, double the time (or decrease the FDD by 30%) and try again.
Table 3-1. mAs Requirements
20 cm 100 cm
kVp
Min mAs Max mA Min mAs Max mA
45 8.42 109.92 209.94 2520.54
50 2.70 50.48 67.46 1261.42
60 0.452 6.318 11.30 157.96
70 0.226 2.342 5.66 58.58
80 0.0852 1.149 2.12 28.98
90 0.062 0.5688 1.55 14.2
Typically, the largest apparent variation in mAs requirements will be due to a kVp error. If doubling the
mAs fails to produce a result, increase the kVp setting (or decrease the FDD) until a result is achieved.
3.4 Initial and Periodic Operation Checks
Generally it is not easy to verify the accuracy of the kVp meter in normal field usage. If care is taken,
either of the methods outlined in the following sections can be used to verify performance of the meter.
Both methods discussed require a careful collection of installation data and periodic measurement of that
data.
Voltage Divider Method
Use the following procedure to perform initial and periodic operation checks of the kVp meter if an x-ray
voltage divider is available:
1. Choose two x-ray systems suited for the test, preferably two different systems, i.e. three phase vs
one phase, falling load vs not, etc. Choosing two dissimilar x-ray machines for the check reduces
the possibility of systematic errors.
NOTE