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dependent changes and thermal response times may be investigated
both in transient handling and during slow handling and stabilized
running sequences. The capabilities of the imaging system must
be matched to the information rate required.
In a radiographic exercise on a development engine it may not
be possible ‘a priori' to determine or specify the exact point in
time when the event may occur within the engine that it is desired
to record, analyse and measure.
For this reason, a real time X-ray television or fluoroscopic
system has been developed (Fig. 5) for use at high energies and
provides a continual surveillance of events within the engine at
T.V. framing rates. This permits a qualitative evaluation of the
engine movements and allows a determination of the point in time
at which the event occurs and also the rate of change of com-
ponent movement. An understanding may thus be achieved of the
mechanism producing the change - for instance thermal or pressure
changes. The images are recorded on a video tape recorder for
subsequent evaluation and analysis and may, if desired, be trans-
ferred to ciné film using teleciné equipment for magnified frame
by frame analysis.
Once the time of occurrence of the event has been determined,
then a film radiograph is exposed to record the event for quan-
titative analysis. Examples of the films used in our programmes
are shown in Fig. 6, and vary from the slow high resolution films
used for steady state radiographs through the medium speed films
to cover the 0.5 to 5 seconds exposure range to the high speed
film capable of exposures within durations of 0.05 to 1.0 sec.
Examples of radiographs produced from our programme are
shown on the light boxes.
The images on the radiographs show a fiducial datum bar which
is arranged adjacent to the cassette and is made of a radio-
opaque material. This is present on the static and all the dynamic
radiographs and permits the differential movements to be determined
in X and Y axes.
For analysis the radiograph is placed on an X-Y co-ordinate table
and using a magnifier and graticule eyepiece, the position of the
component edge is read by the photogrammetrist and punched into the
computer. The radiographs are individually analysed by a single
photogrammetrist who may make multiple readings. They are then
further analysed by other photogrammetrists who punch their
readings into the computer. These are then automatically analysed
and a statistical distribution obtained. Errors or 'rogue' readings
are highlighted and subjected to further examination.
Using this method, despite the apparent subjectivity it pro-
vides reliable data with a typical 95$ confidence interval of
0, 10-0, 15 mm.
However, many problems require greater accuracy or a less
subjective approach and these difficult radiographs are analysed
on a custom made microdensitometer to provide a very accurate
density profile across the area of interest. Suitable algorithms