Wire spring relay
Encyclopedia
A wire spring relay is a type of relay
Relay
A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal , or where several circuits must be controlled...

, primarily manufactured by the Western Electric Company for use by the Bell System
Bell System
The Bell System was the American Bell Telephone Company and then, subsequently, AT&T led system which provided telephone services to much of the United States and Canada from 1877 to 1984, at various times as a monopoly. In 1984, the company was broken up into separate companies, by a U.S...

 in electromechanical telephone exchange
Telephone exchange
In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...

s. It was licenced for use around the world, and was commonplace in Japan. A wire-spring relay has springs made from drawn wires of phosphor bronze, rather than cut from flat sheet metal as in the earlier flat spring relay, and has greater reliability than other types of relays. Wire spring relays were the most suitable relays for logic and computing functions. They were used extensively in marker
Marker (telecommunications)
A marker is a type of special purpose control system that was used in electromechanical telephone central office switches. Central office switches are the large devices that telephone companies use to make the connections that support telephone calls...

s, which were special purpose computers used to route calls in crossbar switch
Crossbar switch
In electronics, a crossbar switch is a switch connecting multiple inputs to multiple outputs in a matrix manner....

 central offices.

Physical Description

A wire spring relay has two major parts, the electromagnet
Electromagnet
An electromagnet is a type of magnet in which the magnetic field is produced by the flow of electric current. The magnetic field disappears when the current is turned off...

 and the contacts. The electromagnet can have an resistance
Electrical resistance
The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...

 of between 15 and 200 ohm
Ohm
The ohm is the SI unit of electrical resistance, named after German physicist Georg Simon Ohm.- Definition :The ohm is defined as a resistance between two points of a conductor when a constant potential difference of 1 volt, applied to these points, produces in the conductor a current of 1 ampere,...

s, and is often designed to operate satisfactorily at a common telephony
Telephony
In telecommunications, telephony encompasses the general use of equipment to provide communication over distances, specifically by connecting telephones to each other....

 voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

, such as 24 or 48 volts.

The electromagnet can also be modified, by the insertion of metallic slugs (lumps) to create a brief delay before pulling in the contacts, or hold the contacts in place briefly after power is removed.

A wire spring relay typically has many contacts, each plated with precious metals such as palladium
Palladium
Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired...

. Each contact is either a fixed contact, which does not move, or is a moving contact, and is made from a short piece of wire. The majority of the wire spring relays manufactured in the 1960s had twelve fixed contacts. Each fixed contact, in the shape of a square box, is mounted on the end of a thick wire stem. A "make" contact, a "break" contact, or both can be provided for each fixed contact. A moving contact consists of two wires projecting out of the base of the relay, bent slightly inwards in order to exert pressure against the armature.

The moving contacts are held away from the fixed contacts by a wooden pattern called a "card". By changing the depth of the cuts on this form, the contacts can be made to make or break earlier or later than others. This can be used to transfer electrical control or power from one source to another by having a "make" contact operate before the corresponding "break" contact does.

Rough adjustments can be made to the fixed contacts as a whole by inserting a screwdriver blade into a slot in the front support structure and twisting as appropriate. This usually suffices to cause the contacts to make and break when they should. In some cases a special tool, known as a "spring bender" to adjust the bend of the springs may be applied to adjust individual fixed or moving contacts.

Use as Logic

Wire spring relays could be interconnected to create the typical combinational
Combinational logic
In digital circuit theory, combinational logic is a type of digital logic which is implemented by boolean circuits, where the output is a pure function of the present input only. This is in contrast to sequential logic, in which the output depends not only on the present input but also on the...

 circuits that were later used in silicon design.

The contacts of one or more relays can be used to drive the coil of another relay. To make an OR gate
OR gate
The OR gate is a digital logic gate that implements logical disjunction - it behaves according to the truth table to the right. A HIGH output results if one or both the inputs to the gate are HIGH . If neither input is HIGH, a LOW output results...

 for example, the contacts of several input relays may be placed in parallel circuits and used to drive the electromagnet of a third relay. This, along with series circuits and more complicated schemes such as multiply wound electromagnets, allows the creation of AND gates, OR gates and Inverters (using the normally closed contact on a relay). Using these simple circuits in combination with De Morgan's Laws, any combinational
Combinational logic
In digital circuit theory, combinational logic is a type of digital logic which is implemented by boolean circuits, where the output is a pure function of the present input only. This is in contrast to sequential logic, in which the output depends not only on the present input but also on the...

 function can be created using relays.

When output wires are fed back as inputs, the result is a feedback loop or sequential circuit that has the potential to consider its own history. Such circuits are often suitable as memories.

Use as Memory

Memory circuits in the form of latches can also be created by having a relay contact complete the circuit of its own coil when operated. The relay will then latch and store the state to which it was driven. With this capability, relays were used to create special purpose computers for telephone switches in the 1930s. These designs were converted, starting in the 1950s, to wire spring relays, making them faster and more reliable. The majority of Wire Spring Relays were used in 5XB switches.

Reed relay
Reed relay
A reed relay is a type of relay that uses an electromagnet to control one or more reed switches. The contacts are of magnetic material and the electromagnet acts directly on them without requiring an armature to move them...

s are better suited to data storage. They were used in conjunction with wire spring relays, for example to store digits for sending to other crossbar switch
Crossbar switch
In electronics, a crossbar switch is a switch connecting multiple inputs to multiple outputs in a matrix manner....

ing offices. In a multi-frequency
Multi-frequency
In telephony, multi-frequency signaling is an outdated, in-band signaling technique. Numbers were represented in a two-out-of-five code for transmission from a multi-frequency sender, to be received by a multi-frequency receiver in a distant telephone exchange...

 sender (the part of a switch which sends routing information about outgoing calls over trunk lines), for example, wire spring relays direct the dialed digits one at a time from reed relay packs to frequency generators, under sequential control of logic implemented with wire spring relays. At the other end, similar relays steered the incoming digits from the tone decoder to a reed relay memory.

Systems

Wire spring relays were also incorporated into the signaling channel units of carrier system
Carrier system
In telecommunication, a carrier system is a multichannel telecommunications system in which a number of individual channels are multiplexed for transmission...

s.

For the Stored Program Control exchange
Stored Program Control exchange
Stored Program Control exchange is the technical name used for telephone exchanges controlled by a computer program stored in the memory of the system. Early exchanges such as Strowger, panel, rotary, and crossbar switches were electromechanical and had no software control...

s of the early 1970s, many relays were made with steel cores that remained magnetized after current ceased to flow in the winding. This "magnetic latching" feature, different from the use of slugs to delay relay operation, was used in the arrays of reed relay
Reed relay
A reed relay is a type of relay that uses an electromagnet to control one or more reed switches. The contacts are of magnetic material and the electromagnet acts directly on them without requiring an armature to move them...

s that switched connection paths in the early models of Electronic Switching System
Electronic switching system
In telecommunications, an electronic switching system is:* A telephone exchange based on the principles of time-division multiplexing of digitized analog signals. An electronic switching system digitizes analog signals from subscriber loops, and interconnects them by assigning the digitized...

s. A miniature wire spring relay was also produced, starting in approximately 1974 as part of the 1A redesign of the 1ESS switch
1ESS switch
The Number One Electronic Switching System, the first large-scale Stored Program Control telephone exchange or Electronic Switching System in the Bell System, was introduced in Succasunna, New Jersey, in May 1965. The switching fabric was composed of reed matrixes controlled by wire spring relays...

.

Manufacturing of wire spring relays greatly declined in the late 20th century due to the introduction of digital electronic switching system
Electronic switching system
In telecommunications, an electronic switching system is:* A telephone exchange based on the principles of time-division multiplexing of digitized analog signals. An electronic switching system digitizes analog signals from subscriber loops, and interconnects them by assigning the digitized...

s that used them in very small numbers.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK