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Solid State Relay Modules
July 2021

Why Solid State Relays are used?

Solid State Relays (SSRs) by their nature are electronic switching devices which contain no moving parts. This lack of mechanical or physical movement for switching is a key advantage over Electromechanical Switching relays. Following are the key advantages of solid state relay modules.

1 -  High operating frequency
2 -  Contact chattering free operations.
3 -  Extended life.

One of the major advantages of having no moving parts is that SSRs offer very fast response times with no contact bounce and no mechanical noise. Command signal application to a control circuit and output circuit turn on is usually in microseconds.

How do Solid State Relays work?

Solid State Relay Blog Drawing


A quick look at the circuit diagram shows how a typical Solid State Relay module contains two terminals each at input and output. Generally, Solid State Relays employ Opto coupler based switching which ensures isolation between input & output.

DC-AC Type configuration.
In this configuration, the input is always DC and Output is AC. The input circuitry is operated on DC circuit whereas the switching load is AC type. At the input side, there is a polarity, however, there is no need to check for the polarity if DIAC based circuitry is employed for switching.

DC-DC type configuration.
In this configuration, the input as well output current is DC, both having a polarity requirement. If voltage other than DC is applied, the relay may be damaged. The DC input is applied to the optocoupler. At output, DC type switching is used for loads.

AC-AC type configuration.
Optocouplers are always operated by DC voltage not by AC voltage. Therefore in this type of relay, the supply is first rectified to DC and then applied to opto for switching. On the output side, the AC load is connected.

AC-DC configuration.
In this configuration, a rectifier circuit is used at the input. At the output, a DC switching circuitry is used to switch the load.

Applications of the Solid State Relays

Today, SSRs find applications in virtually every industry because of their high responsiveness low turn on power consumption. Generally they are used in similar spaces as electro-mechanically relay modules for switching, protection and switching applications.

Solid State Relays find applications in:
1 -  Load Switching
2 -  Protection of DI/DO
3 -  Isolation between Input and Output

Industrial segments where Solid State Relays are used include:

1 -  DCS applications
2 -  Solenoid valve switching
3 -  High inductive load components such as motors
4 -  High frequency switching such as printers
5 -  Controlling lights, fans and such devices
6 -  Communication lines

Choosing Connectwell Solid State Relays

For new industrial applications or to upgrade to a more modern standard, Connectwell solid state relay modules offer highly responsive performances with greater precision in power to load application and removal. Choosing Solid State Relays over Electromechanical relays offers advantages of high frequency switching, high inductive load switching and zero cross over switching.

Explore the wide range of Connectwell Solid State Relay modules or contact us to have your specific input output configuration needs addressed.

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