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Application of Relays

A relay is able to control an output circuit of higher power than the input circuit, it can be considered to be, in a broad sense, a form of an electrical amplifier. It is one kind of useful electrical component. Different types of relays can be used in various field.

Relays can control a high-voltage circuit with a low-voltage signal, so it is uesed for some types of modems or audio amplifiers.

Relays can control a high-current circuit with a low-current signal, so it is uesed for the starter solenoid of an automobile.

Protection relays can detect and isolate faults on transmission and distribution lines by opening and closing circuit breakers. It isolate the controlling circuit from the controlled circuit when the two are at different potentials. For example when controlling a mains-powered device from a low-voltage switch. The latter is often applied to control office lighting as the low voltage wires are easily installed in partitions, which may be often moved as needs change. They may also be controlled by room occupancy detectors in an effort to conserve energy.

Relays have logic functions. For example, the boolean AND function is realised by connecting normally open relay contacts in series, the OR function by connecting normally open contacts in parallel. The change-over or Form C contacts perform the XOR (exclusive or) function. Similar functions for NAND and NOR are accomplished using normally closed contacts. The Ladder programming language is often used for designing relay logic networks. It is used as logical elements in early digital computing. Because relays are much more resistant than semiconductors to nuclear radiation, they are also widely used in safety-critical logic, such as the control panels of radioactive waste-handling machinery.

Relays have time delay functions. Relays can be modified to delay opening or delay closing a set of contacts. Between the armature and moving blade assembly use a copper disk, resulting a very short, about a fraction of a second delay . Current flowing in the disk maintains magnetic field for a short time, lengthening release time. If for a slightly longer, aboat up to a minute delay, a dashpot, which is a piston filled with fluid that is allowed to escape slowly, is used. The time period can be varied by increasing or decreasing the flow rate. For longer time periods, a mechanical clockwork timer is installed.

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