Who invented relay

Some will say that it is a type of protection device, some say it is a transmission device and even some say it is a type of race relay race. But what does is it really mean? Merriam-Webster says: a relay is.

So from this definition we understand, a relay is a device with which you can operate high power devices at low voltage. Now that we know what a relay is, lets get to know when it was first used.

American scientist Joseph Henry is often claimed to have invented a relay in in order to improve his version of the electrical telegraph, developed earlier in It is claimed that English inventor Edward Davy "certainly invented the electric relay in his electric telegraph c.

A simple device, which is now called a relay, was included in the original telegraph patent of Samuel Morse. The mechanism described acted as a digital amplifier, repeating the telegraph signal, and thus allowing signals to be propagated as far as desired. So, all in all, the term relay has been around since the start of the nineteenth century.

A relay is made up of a few parts, which can be separated into an Electromagnet, a movable armature, contacts, yoke, and a frame. The figure below shows the construction of a relay. The electromagnetic relay essentially consists of a coil to which a voltage is applied, a core upon which the coil is wound, relay contacts, and a movable steel armature which is held against one of the contacts by means of the spring.

Before the voltage is applied to the coil the relay is said to be in its normal or de-energized position. Its action depends on the interaction of the magnetic field set up by the coil carrying the current and the movable steel armature. In the relay shown in Fig. When you apply voltage to the coil, the relay gets energized and the magnetic field set up around the coil makes the armature to be attracted toward it.

Contact 4 breaks with terminal 3 but makes with terminal 2, and any external controlled circuit connected between terminals 1 and 2 is now completed. The relay remains in the position till the coil remains energized. The schematic interpretation of this basic relay is illustrated in Fig. Terminals 2 and 3 are the fixed contacts, and terminal 1 is connected to the movable armature in some relays the armature remains isolated from all contacts.

The contacts of the basic relay act as single pole double throw SPDT switch. Although switch contacts are manually controlled, relay contacts are remotely controlled. Other than the Electromagnetic relay there are many other types of relays that work on different principles. Its classification is as follows:.

When two different materials are joined together it forms into a bimetallic strip. The armature is connected to one or more moving contacts and it is attached to the yoke with the help of a hinge. This armature is held in a place with the help of spring such that whenever the relay is in the de-energized condition the air gap is present in the magnetic circuit. In these conditions of the sets of a relay are made closed and the other one kept open.

When the electric current is passed through the solenoid it activates the armature by producing the magnetic field and the movable contacts that are moving consequently either makes or breaks the contact depending on the construction. In the case when the relay is de-energized then the contact is opened by the movement and the connection breaks and a vice versa situation occurs if the contacts were open.

The armature returns by a force when the current is switched off, this force is approximately half as that of the magnetic field in the relaxed position. Most of the relays are designed to operate quickly. In the cases when the coil s energized the resistor or a diode is placed across to it in order to dissipate the energy from the magnetic field that is collapsing at the deactivation else, it would be dangerous to the semiconductor circuit.

It was not used before the application of transistors are relay drivers but when the germanium transistors were getting destroyed due to this reason the diodes were used to dissipate the energy. Whereas the resistors are more durable than compared to that of the diodes and are also less efficient in order to eliminate the voltage spikes that are generated by the relays.

When the relay is driving the large reactive load then a similar problem of the surge currents occurs around the output contacts of the relay.

In this case, in order to absorb the surge, a snubber circuit is used, which is a combination of resistor and capacitor that are placed in series with the contacts.

If the coil is designed in order to energize with the alternating current, then a method is used to split the flux into the two out-of-phase components that are added together. This in turn increases the minimum pull during the armature in the AC cycle. This is done with the help of a small copper shading ring that is crimped around the portion of the core that creates the delay in the out-of-phase component.

The contact materials that are used for the relays vary depending on the application. Material that has a low contact resistance may be oxidized in the air or it may stick instead of cleanly parting while opening. The machine he had in mind would resemble a music box, with a barrel surrounded by a number of protruding pins. On one side of the barrel was a dial inscribed with the letters of the alphabet.

One such device would sit at each end of the telegraph. A wound spring could make each barrel turn, but most of the time a detent would hold them in place. When the telegraph key was depressed, it closed the circuit, activating electromagnets to release both detents, allowing both machines to turn.

Once the desired letter was showing on each dial the key was released and the detents dropped, stopping the motion of the barrels. Cooke realized that a similar mechanism could be used to solve another longstanding problem in telegraphy — how to notify the receiver that a message was incoming. A second circuit with another electromagnet and detent could be used to activate a mechanical alarm bell: close the circuit, pull up the detent, and the alarm rings.

In March of , Cooke began collaborating with Wheatstone on telegraphy, and around that time one or both of the partners conceived of the secondary circuit.

Rather than having an independent circuit for the alarm and the miles of wire that entailed , why not simply use the primary telegraphic circuit to also control the alarm circuit? By this time Cooke and Wheatstone were back to needle-based designs, and it was straightforward to attach a small piece of wire to the back of the needle so that, when its tip was pulled up by electromagnetism, its tail would close a second circuit.

This circuit would set off the alarm. After a decent interval allowing the receiver to rouse himself from his nap, disconnect the alarm, and prepare pencil and paper , the needle could then be used to signal a message in the usual fashion.

Twice on two continents in the span of two years for two different reasons, someone had realized that an electromagnet could be used as a switch to control another circuit.

But there was another way of thinking about the relationship between the two circuits. By the fall of Samuel Morse had confidence that his idea for an electric telegraph could be made to work. However, to prove to Congress that his telegraph could span the continent, he needed to do a great deal more than that.

It was clear that, however powerful the battery, at some point the circuit would become too long to provide a legible signal at the far end. But Morse realized that even with its potency greatly diminished by distance, an electromagnet could open and close another circuit powered by a separate battery, which could then send the signal on.

This process could be repeated as many times as necessary to span arbitrary distances. Hence the name relay for these intermediary magnets — like a relay horse, they take the electrical message from their fatigued partner and carry it forward with renewed vigor. He saw the relay not as a switch but as an amplifier, which could turn a weak signal into a strong one. Across the Atlantic and around the same time, Edward Davy, a London pharmacist, had the same notion.

Davy probably began tinkering with telegraphy sometime in As he wrote many years later: 7. But he sailed to Australia in to escape a failed marriage, leaving the field in Britain clear for his rivals. Their telegraph company bought up his idle patent several years later. We tend to pay a great deal of attention to systems in the history of technology, while rather neglecting their components. We chronicle the history of the telegraph, the telephone, the electric light, and bathe their creators or those who we deem retrospectively as such in the warm rays of our approbation.

Yet these systems are made possible only by the combination, recombination, or slight modification of existing elements which have quietly grown in the shade. The relay is just such an element. From its ancestral forms, it quickly evolved and diversified as telegraph networks began to grow in earnest in the s and 50s. It then found its way into electrical systems of all kinds over the following century. The earliest change was the use of a stiff metal armature, like that in the telegraph sounder, to close the circuit.

A spring pulled the armature away from the circuit when the electromagnet was off. Default-closed models were also devised, as complements to the original default-open design. They were very useful, though, for joining a low-current long-distance line to a high-current local circuit that could be used to power other machinery, like the Morse register. Dozens of U. The differential relay, which split the coil so that it the electromagnetic effect was canceled in one direction but reinforced in the other, enabled a form of duplex telegraphy: two signals passing in opposite directions over a single wire.

Thomas Edison used the polarized or polar relay to make his quadruplex, w hich could send 4 simultaneous signals over a single wire: two in each direction. Permanent magnets also allowed for the creation of latches , relays which would stay open or closed, whichever way they were last set.

In addition to their role in new telegraphic equipment, relays also became essential components of railway signaling systems. When electrical power networks began to appear at the end of the century, they found uses in those circuits, too — especially as fault-protection devices.

Yet even these networks, vast and complex as they may seem, did not demand of the relay more than it could give.