Technical realization of the basic logical functions by electronic means
When considering the different logical systems in use at present, one is first of all struck by the large number and in particular by the great variety of technical variants. Apart from the electrical logical systems, there is a whole range of non-electrical ones, which operate pneumatically or hydraulically.1, 2 The electrical systems can be further subdivided into those with mechanical contacts (relays, remote control switches, mechanical switches, etc.) and those with contactless switches (vacuum tubes, cold cathode tubes, semiconductor devices). Each type of system has its special advantages and disadvantages. For example, relay circuits do not allow high switching rates, but they do have the very considerable advantage that they are completely insensitive to parasitic voltages. Hydraulic or pneumatic logical units are particularly suitable for use in atmospheres where there is a risk of explosion.
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