General Purpose Relays Overview

general purpose relay

Relays are such common devices that it would be nearly impossible to conceive of a day when somebody didn't interact with one in some regard. In apartment complexes where somebody "buzzes" someone in, it's likely that there is an electrically operated relay in use that opens and closes the door that the visitor passes through.

Relays are also utilized in alarm systems, safety circuits for household electricity and more. In fact, relays have been in use for well over 100 years, being used on telegraph systems in among their earliest applications. While these devices have become more advanced and capable of handling higher frequency operation as time has progressed, they remain, in many regards, quite similar to their original designs.

Relays are sometimes called relay switches. They are also known as contactors, depending upon the size and scale of the device in question. Relays are utilized in everything from the smallest consumer devices to the largest machinery in the most advanced industries in the world. Many electronic devices simply could not be manufactured without them and the amazing simplicity of their operation is one of the things that makes these electrical components distinctive, easy to understand and convenient solutions to many different problems.

While they may still be in widespread use, relays have been replaced in some applications. They had an important role in the early days of computing, but they have been largely replaced by more advanced solutions to the role that they originally played. Relays have also become advanced in other ways over the years, but their core functionality remains the same. When a circuit needs to be powered or de-powered without the user having to intervene and manually throw a switch, a relay is generally the best available solution and one for which there are many variations, allowing a great degree of customization.

What is a Relay?

In the simplest terms, a relay is a type of switch that is operated electrically. These devices employ various means of operating the switch, but an electromagnet is a very common solution to this.

Relays have many different uses and are very common electrical components. They are often utilized in situations where isolation is necessary or when a circuit needs to be controlled with a low-power signal. Among the first uses of the relay was in telegraph lines. The relay would be utilized to repeat a signal that came in from a given telegraph circuit and would retransmit that message to another circuit.

There are specialized types of relays that are utilized for very high power applications. These are generally referred to as contactors. There are also relays available that don't have any moving parts in them, which are referred to as solid-state relays. These utilize semiconductors rather than moving parts.

Relays are often utilized as protection devices, breaking a circuit in the event of an overcurrent condition or another potential disaster. There are newer versions of these types of relays, which lack the mechanical components, but which are still referred to as relays normally.

The function that a relay performs that is most useful to electronic designers and engineers is its most basic function; that of any electronically controlled switch. This makes it particularly useful in applications where the main advantage is really convenience. For instance, radio operators depend upon relays to provide the basic function of their equipment. When a radio operator is receiving a signal, that signal is routed through electronics that allow it to be interpreted and represented as sound from the loudspeaker. When the radio operator is transmitting, the utilize a different circuitry that has far higher power than the receiver circuitry. Using a relay, electrical current can be shunted off from the transmitting or receiving circuit as needed, allowing operation of the device.

What are General Purpose Relays?

general purpose relayGeneral-purpose relays are not specialized types of relays that can be used for multiple applications. They include many different designs. Solid-state designs, mechanical designs and other designs are all included among the various options available.

General-purpose relays are such basic electrical components that most designers and engineers will have a variety of them available in their building kits.

General-purpose relays can generally be understood to provide one of two functions. They either provide a function wherein the condition of the relay is temporarily changed upon the introduction of current into the circuit and where the condition of the circuit reverts back to its original condition after current is removed. Other relays change their position when current is added to the circuit and remain in the new position until current is introduced into the circuit again. These types of relays are referred to as non-latching and latching relays, respectively.

What Types of General Purpose Relays Exist?

There are several different types of general-purpose relays on the market. All of these have their own applications, but they are versatile enough that they can be used in a variety of different ways to create useful electronic devices.

One of the distinctive characteristics of relays as electrical components is that they can come in many different sizes. Some relays are exceptionally large devices, such as the contactors referenced before. Other relays are very small; so small that they can be surface mounted onto printed circuit boards where they provide their function.

High Frequency & RF Relays

High frequency and RF relays utilize radio signals to perform switching functions. These are passive electronic components that are utilized in testing equipment and in other applications. Solid-state versions of these relays are available.

RF relays are specifically utilized in radio applications. These types of relays are often employed on testing equipment and, of course, on radio broadcasting equipment. Radios have separate circuit systems in them that need to be activated when transmitting and receiving and radiofrequency relays provide the functionality that allows this to take place.

What are High Frequency Relays?

electromechanical relayFrequencies utilized in electronic devices are continually increasing. High-frequency relays provide a way to isolate circuits in a high-frequency environment. These are devices that are commonly used in radio applications and in other electronic applications.

How do High Frequency Relays function?

The simplest example of a high-frequency relay is in a radio. Because the transmitter and the receiver utilize vastly different amounts of power, the circuits need to be isolated. The high-frequency relay provides a way to insulate the receiving circuitry from the transmitting circuitry. This prevents issues related to damaging the electronics, and in some applications, it provides a way to limit crosstalk.

What are High Frequency Relays used for?

High-frequency relays can be utilized in any application where electronic signal is being produced at a very high frequency, obviously, and that generally means use in radio. In computers or other machinery were very high frequency signals are present and need to provide information that is used to switch circuitry, these types of relays may also be used.

A high-frequency relay can be thought of as a relay that is simply capable of changing its state at a very high rate of speed. This is particularly useful in a world where computers and other equipment is becoming much faster and more efficient and where electrical components have to keep pace with that.

What are Latching Relays?

latching relay is a relay that remains in the state it was last in when it was triggered. For example, if a relay is normally open but, due to an overcurrent condition, the relay needs to be closed, allowing current to be shunted off to a different circuit, that relay will remain closed until it is manually moved back to its original position.

Latching relays, like all relays, are really just switches. These are switches that remain in the position they were placed in last. These relays are also known by the terms "keep" and "state".

How Do Latching Relays Function?

mount latching relayA latching relay contains a solenoid. The solenoid operates a ratchet and cam mechanism, or it may work with a center spring and a permanent magnet. There are other types of latching relays with more specialized purposes. For example, a stepping relay is a relay that moves through a series of predetermined steps every time its state is changed and remains on the last step after power is removed.

Latching relays have an important role in the history of computing. Early on when computers were being designed, latching relays were actually used for memory. The state of the relay can correspond to the state of a bit, providing an easy way to store information in a computer system.

What Are Latching Relays Used For?

Latching relays have many different uses. One of the primary advantages of this type of a relay is the fact that, when power is removed, it remains in its last state. This makes it ideal for isolating and for safety applications.

A latching relay may be used in any application where the condition of the relay should not change unless current is introduced into the circuit. In addition to the aforementioned safety applications, this can be a feature that is utilized in many different designs, owing to the fact that the position of the relay is always predictable.

Latching relays are also used in industrial settings. These are frequently used as ways to protect equipment from electrical damage. They are also utilized in a type of circuit breaker called an earth leakage circuit breaker. These types of circuit breakers are able to monitor for voltages in the enclosures around electrical equipment. Once they detect a leakage, the relay is tripped and, because it is a safety relay, it will generally be a latching design that were remain off until it is reset by the user.

These types of relays are also found in the household. Many outlets, particularly in laboratories, have this type of relay installed on the socket, which prevents death from electric shock by instantly breaking a circuit when an overcurrent condition is detected. In order to restore the circuit to operating condition, the relay needs to be manually reset.

What are Non-Latching Relays?

Non-latching relays go back to their original state after they have been tripped. These are very simple devices. Due to their mechanical simplicity, non-latching relays are typically less expensive than latching relays.

How Do Non-Latching Relays Function?

In a non-latching relay, when a current is introduced, it passes through a coil that generates a magnetic field. That magnetic field operates an armature that closes or opens the electric circuit to which it is attached. Once the current is removed from the relay, the magnetic field is dissipated and the armature slides back into its original position.

Non-latching relays that are of the stepping variety move through a series of positions as current is introduced into the line. This made them very common solutions for telecom applications in the past, though digital technology has largely displaced them in this regard.

What Are Non-latching Relays Used For?

non latching relayNon-latching relays are often employed in situations where cost is more important than function. Because they cost considerably less than latching relays, they are often used as a way to save money on a project.

A non-latching relay is also utilized when the relay needs to be reset to its original position when power is removed from the circuit. This can be advantageous or disadvantageous.

In safety situations, an unplanned removal of power may result in the relay switching to the wrong condition. This is why latching relays are generally used in safety applications.

If the power loss is intentional, however, non-latching relays can provide very cost effective solutions to isolation, safety and other issues.

Non-latching relays can also be utilized in security applications. For instance, in an electric door lock, the relay may be opened up when current is put through the circuitry and, upon that current being removed, the door can revert to its normal, locked position. This prevents situations where security is compromised by an operator not closing the relay - locking the door - after someone has been allowed through.