Signal relays are electrically operated switches that are used to control the flow of electricity in an electrical system or circuit. Today, we’ll discuss how they work and how they can be used in your projects.
The most simple signal relays are electromagnetic switches. When current is supplied to the electromagnet, it pulls the switch open or closed. The first relays were used in the 19th century. The most famous example is when Samuel Morse utilized them to send communications across long distances. Using the now famous Morse Code, he could send signals tapped out on a switch in one location to control a relay at the other.
These relays were also used in early computing devices. In fact, the first time an actual bug was found in a computer system occurred when a moth stuck in a relay prevented it from working correctly. Now, of course, there are no electromagnetic relays in the computers we use. In fact, electromagnetic relays, in general, have given way to solid-state counterparts.
Applications of Signal Relays
Signal relays have a wide range of uses in electronic and electrical systems that need to control electrical flow. Some of the ways in which devices use them include:
- Switching signals between different circuits or components
- Amplifying weak signals
- Isolating one circuit from another to prevent interference or damage
- Controlling the operation of motors, lights, or other high-power devices
- Selecting different inputs or outputs in a multi-channel system
- Safely switching high-voltage or high-current circuits
- Providing a fail-safe mechanism in case of power loss or component failure.
You’ll find these applications of relays put to use in a number of industries. Some of the most common places you’ll find relays include industrial control systems, telecommunications, automotive electronics, and medical equipment. They work well in situations that require precise control, low power consumption, and high reliability.
The application of relays can be separated into two categories: power relays and signal relays. Power relays, typically capable of handling high voltages and currents, can help control the flow of power in a circuit. Signal relays, on the other hand, control the flow of some signal that the circuit is operating on.
Types of Signal Relays
Three major signal relays are available: electromagnetic, reed, and solid-state. The exact function of the relay depends on the type. Each type of relay also comes with a set of advantages and disadvantages. Below, we’ll describe each of the types and some of the strengths and weaknesses of each. In a later section, we’ll go into more detail on how to pick the right one for your needs.
1. Electromagnetic Relays
These are the most basic forms of a relay. A coil of wire, similar to the electromagnets you may have seen in science class as a kid, provides the core functionality. The switch itself is a metal armature controlled by the magnet. Turning the magnet on or off moves the armature, opening or closing the circuit. Electromagnetic relays are inexpensive and can be designed to handle large currents and high voltages. However, the reliance on the metal armature makes it slow compared to other options.
2. Reed Relays
This type of relay forgoes the coil of wire and armature and uses a reed switch instead. In these relays, the switch itself is the electromagnet. Two thin electromagnetic reeds are activated to pull themselves closed or open. Switching in this way always causes reed relays to be significantly faster than electromagnetic relays and less prone to wear and tear.
But they have the downside of being able to handle less current than their more mechanical counterparts. The mechanical contacts can also wear out, reducing the reliability of the relay. They typically only work well with low-power applications and are more prone to electromagnetic interference.
3. Solid-State Relays
This type of relay relies on transistors and other solid-state technology to perform the switching. As a purely solid-state device, there is no electromechanical switching at all in these devices. As such, they are immune to the effects of mechanical wear and tear. The lack of mechanical actuation also means solid-state relays can operate as fast as the electric signals can change.
However, solid-state relays have some downsides, as well. They are the most expensive of the options, have high output resistance, and are not suitable for switching very low signals, like those found in audio applications.
How to Select Signal Relays for Your Design
When shopping for a signal relay, you’ll find that it comes in a large variety of options. Understanding these options and how they impact your design is an important part of picking the right relay for your needs. Below are some of the important considerations you should take into account when choosing a relay for your electrical circuits.
- Voltage Rating: Each relay is rated to operate under different voltages. The relay you choose must match the voltage of the circuit it will be used in.
- Current Rating: In addition to voltage rating, the relay should be able to handle the circuit’s current. Be sure to choose a relay with a current rating that is safe for the load you’re switching.
- Switching Time: The switching time of the relay is important if the application requires precise timing. Choose a relay with a switching time that meets the requirements of your application.
- Coil Voltage: The coil voltage is the voltage required to energize the relay and activate the contacts. Choose a relay with a coil voltage that matches the voltage of your circuit’s power supply.
- Operating Temperature: Make sure to choose a relay that can operate reliably in the temperature range of your application. Consider both the ambient temperature and the temperature generated by the load being switched.
- Contact Configuration: Relays come in various contact configurations, such as normally open (NO), normally closed (NC), and changeover (CO). The one you choose should match the default state your application requires.
- Size and Mounting: Consider the relay’s physical size and mounting options, as well as any space constraints in your application.
Find Your Signal Relays With PartStack
Although they’re one of the earliest electrical devices, signal relays retain an important role across a large number of industries. This article has just scratched the surface of what you can learn about the topic. But we hope it has provided enough information to show you how these devices can aid in your project designs.
Find reliable and efficient signal relays from brands like Omron, TE Connectivity, Siemens, and more on PartStack Marketplace. Compare prices, read reviews, and buy with confidence.
