Fluke Biomedical 07-492 - Manual (Page 12)

Nuclear Associates 07-492
Operators Manual
3-2
Figure 3-1. Detector Positioning
3.4 Determining mAs Requirements
The mAs minimum requirements as a function of distance and kVp are indicated in Figure 3-2. When the
mA has been determined from the chart as discussed in this section, the mAs should be calculated using
an exposure time of 50 ms (1/20 second) or greater.
The curves in Figure 3-2 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 4, Theory of Operation, for a detailed discussion.)
Use the following guidelines to determine the required mAs from the graph in Figure 3-2:
1. Locate the kVp to be measured on the horizontal axis.
2. From the kVp point on the axis, move vertically to the selected FDD curve.
3. From the kVp position on the appropriate FDD curve, move horizontally to the vertical axis and the
read the required mAs.
4. If necessary, interpolate between distances using the inverse square law.
The curves in Figure 3-2 are derived from single-phase measurements. Three phase machines will
generally require 70% of the mAs determined from the curves.
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 the determined kVp fails to produce a result, double the time (or decrease the FDD by 30%) and try
again.