The Electronic Switch

Abstract

In some investigations it is required to indicate not merely the dependence of one magnitude on time (or some other magnitude) but also to observe the trend of two or even more processes simultaneously. If these are cyclic processes, a multi-ray oscilloscope is not essential; a single-ray oscilloscope can be employed. If, for example, photographic records are desired, it is merely necessary to switch in the various processes in succession and to take a photograph of each. It is then an essential condition that, when the dependence on time of the processes is being shown, the time deflection in all photographs is always rigidly locked in phase with some reference value. Fig. 9-1, which will be discussed in more detail later, shows this circuit. To facilitate observation it is essential to switch from one signal to the other so rapidly that discontinuities of the patterns are not perceptible or, at least, not obtrusive. The impression of continuity can be much improved by using oscilloscope tubes of very long persistence. Tubes with N (P2) and P (P7) screens such as DN 10-78, DP 10-78 or DN 13-79 are particularly suitable. As the stimulation light of the P-tubes is blue-white, but the afterglow is yellow, the light fluctuations at low switching frequencies can be reduced by means of an orange-yellow filter. Thus it is possible to display two processes simultaneously by means of a simple switching relay. Rotary switches have also been used, particularly if the waveforms of several magnitudes are to be displayed at the same time. An important example is the display of several characteristic curves intended to show the dependence of one magnitude on another and also the influence of a parameter [1].