Relays are a fundamental building block of modern electronic circuits. It’s no exaggeration to say that without them, the world as it is would cease to function.
Put simply, a relay is a form of electrically operated switch. It allows a small electrical signal to control a much larger one. This can be very useful in a whole range of designs, not least because of the relay’s ability to isolate large alternating currents from the mechanical switch being activated by a human being.
But relaysvary considerably in their uses, and their types. Knowing which is right for your application often means understanding the options.
Electromechanical Relays (EMRs)
An electromechanical relay does rely on physical moving parts, but it’s a little more sophisticated than a simple switch. Often, you’ll find a spring, which is designed to pull the contacts away from one another, and an electromagnet, which is there to pull them together. When a current is passed through the latter, the switch closes.
Solid-State Relays (SSRs)
What if you need your relay to perform many, many switches every second? In this case, a mechanical component would be too slow, and vulnerable to rapid wear and tear. This is where solid-state relays can be so effective. Widely used in automation systems, they can switch very quickly.
Thermal Relays
In some cases, you might want a relay that will switch when the environment reaches a certain state. Most commonly, circuits might need to be broken when the temperature reaches a given threshold, in order to prevent damage to more sensitive components. This is where a thermal relay is ideal. It’s often used to safeguard motors, and acts to protect not just systems, but the people using them.
Reed Relays
Finally, it’s worth mentioning the so-called ‘reed’ relay. This is a little bit like the traditional electromechanical relay, except that there’s no armature moving the contacts. Instead, the contacts themselves are made of magnetic material. They’re protected against corrosion, traditionally using a glass tube.
These relays have been around since the 1930s. Their appeal has endured largely because they are so simple, and so rarely ever need to be replaced. While these devices are no longer used in telecommunications, where they once predominated, they are still found in other applications, where their low leakage current and extreme reliability really matter.
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