Switching and counting

Abstract

Electrical or electronic switching is the act of controlling the passage of electrical power, or of signals carrying intelligence, from one subunit to another. There are many forms of switching, one or more of which can be applied to any switching device or circuit. These forms include remote or direct switching, manual or automatic switching, high speed or slow speed switching. The simplest and best known switch is the kind that is used for controlling mains electricity not only in low power domestic circuits but also in electronic systems such as oscillators, oscilloscopes, radios, televisions etc. This switch, which controls one supply line (the live wire) is a manually operated, slow speed, direct switch and is a mechanical device in which contacts move. For circuits in which voltage and current levels are higher and therefore offer a greater risk to the operator, remote switching is used. In remote switches a low power circuit controls a high power circuit, the low power circuit being operated either automatically or manually. Electromagnetic relays are an example of slow speed remote switches, the slowness being due to the presence of moving parts; thyratrons and thyristors are examples of remote switches operating at higher speeds due to the absence of moving parts. Very high speeds are achieved using specially constructed solid state devices made in integrated-circuit form. High speed switching and counting techniques are used in computing and in a variety of processes (such as industrial control) where the frequent and rapid measurement and monitoring of variable quantities is necessary.