Operating Manual

The “density-thickness (preliminary) charts” as described, provide the data needed to

prepare the final exposure chart. In order to eliminate any inaccuracies, an intermediate

chart (based on the preliminary charts) is prepared for density 2, using the data already

recorded in the first charts.

This is how the “thickness-tube voltage chart” of figure 3-9 is arrived at. Points relating to

the same series of exposures are then joined in a smooth line producing the intermediate

curves for 8 mA.min and 200 mA.min. In this way deviations in the results of any of the

radiographs can be compensated for.

Preliminary charts

Before producing an exposure chart it is useful to first draw up preliminary charts, the

so-called “density-thickness chart” for the voltage range of the specific X-ray set and a

“kV- thickness chart”.

The two preliminary charts are produced on the basis of the following data:

1. X-ray set: tube voltage 60-200 kV, tube current 5-10 mA

2. Filter: none

3. Source-to-film distance: 80 cm

4. Material: steel

5. Intensifying screens: none

6. Type of film: D7

7. Density: 2.0

8. Development: automatic, 8 minutes at 28°C in G135 developer

Exposures

Using a tube current of say 8 mA and an exposure time of 1 minute (i.e. 8 mA.min) radio-

graphs of the step wedge are made at voltages of, for example 75, 90, 105, 120, 135, 150,

165, 180 and 195 kV. Only a narrow strip of the film is used for each exposure. The same

process is repeated at, say 10 mA with an exposure of 20 minutes (i.e. 200 mA.min).

Measuring the density

After development of the radiographs, the density of all steps is measured by a densitome-

ter, see section 9.2.

Drawing up the preliminary charts

The densities measured are plotted graphically against the material thickness for

which they were obtained. A smoothly curved line then joins the points relating to one

particular voltage. The result is two preliminary charts (figure 2-9), made at 8 mA.min and

200 mA.min.

Fig. 2-9. Density-thickness preliminary charts

Fig. 3-9. Thickness versus tube-voltage preliminary chart

density=2