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Previous discharge circuit
Delay circuit
Control circuitof krypton
tube
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Fig. 25. Circuit diagram of one stage of LCA 30-flash generator.
fires and triggers the krypton-tube discharge circuit. In this case, the high voltage is only 15 kv. As the krypton tube breakdown voltage is only 2.5 kv it is mounted in series with an auxiliary spark-gap S, which is triggered in the usual manner by means of a control electrode and a pulse transformer. Firing of the tube is assisted by a few turns of wire wound round the glass envelope.
Figure 26 shows this 30-flash generator. On the front can be seen the orientable plastic holder for the 30 krypton tubes. The power supply is housed at the bottom of the cabinet. Each of the 30 discharge and delay circuits may be quickly removed and replaced individually; they are all interchangeable. But the actual constructional unit of the instrument is a group of six such circuits, so that instruments may be delivered with any number of flashes equal to a
multiple of six, up to 30. Two 30-flash instruments have been made to date at an approximate cost of $6000 each, one for our own laboratory, the other for another DEFA establishment. A 24-flash unit has just been delivered to the Swedish armament research organization. A slightly different 18-flash unit was delivered last year to the research laboratories of the French Coal Industry Organization.
Figure 27 shows a typical schlieren exposure produced by the 18-picture instrument.
This method of analysis of high-speed phenomena has the advantage of yielding high-definition images, irrespective of the picture rate, as there is no moving part in the optical system. The small number of pictures is largely compensated for by the fact that it is possible to start the sequence precisely at the beginning of the interesting phase of the
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May 1953 Journal of the SMPTE Vol. 60