Why Choose Solid State Relays for Your Process Control System?

by | Jul 8, 2016 | Instrumentation

Relays are an important part of most industrial control systems. Any time power must be sent or turned off to a device, a relay can take care of the switching automatically. This prevents the need for manual switching which is not only time consuming, but almost impossible with most modern industrial and manufacturing processes today. In most cases, you can go with mechanical or solid state relays (like ones from Carlo Gavazzi distributors). So which is the best choice for your business and why? Let’s enter the world of relays to find out.

What is a Relay?

A relay works like participants in a relay race, as they hand off an item from one person to another. Relays can take power intended for a motor, heater or other system components and stop the power from getting there or relay it on. For a long time, the only kind of relay was a mechanical device.

How Mechanical Relays Work

A mechanical relay works on the principle of electromagnetism. They have two sets of metal contacts. One set is attached to a coil of wire and the contacts are normally open (apart from each other). When current is applied to the coils, it turns the first contact into a magnet and the two contacts are attracted together. If a wire is connected to each contact, this will complete a circuit. When current is removed from the coil of wire, there is no longer a magnetic attraction and the two contacts come apart, opening the circuit.

Solid State Relays

If you go to a controller source like Carlo Gavazzi distributors, you’ll find some excellent solid state relays. These relays work differently than the mechanical types. A solid state unit achieves the same purpose of a mechanical relay (switching) but there are no metal contacts or moving parts. SSR’s have three main components:

Sensor – receives the control signal

Switching device – solid state mechanism which switches power off electronically using semiconductors
Coupling – activates switching without the need for contacts

SSR Benefits

There are several important benefits of using solid state relays:

  • No electromagnetic interference
  • Silent operation – standard relays make a clicking sound each time a switch occurs.
  • Smaller profile – SSRs are smaller than mechanical relays and can save space.
  • Durability – much less sensitive to factors like humidity and vibration and in an industrial environment this is a huge advantage.


When SSRs fail they usually short out. However, mechanical ones usually fail in the “open” position. SSRs also generate higher resistance when closed and less resistance when open. When shopping for control components, Carlo Gavazzi distributors can show you the best solid state relay applications for your business.

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