Solid State Relay Working Principle

The inputs and the output of the relay are attached to the specified terminals.

Solid state relay working principle. To activate contacts it is necessary to have an activator. Its role in the solid state relay is performed by a semiconductor or solid state device. When the input signal is activated the internal zero crossing detector circuit triggers the triac to turn on as the ac load voltage crosses zero. The principle of operation of a solid state relay is the closing or opening of contacts which transmit the voltage directly to the relay.

When a specific control signal is provided to the input terminals of the solid state relay the on and off function on the output terminal is performed accordingly and after. Since the 4 20ma or 0 10vdc control input of the analog relay can be varied the output operates in accordance with the phase control principle. It can achieve switching on and off with no contact and no spark due to the switching characteristics of electrical element i e. The transfer function is linearized and reproducible.

The load current is maintained by the triac s latching effect after the input signal is deactivated until the triac is turned off when the load voltage crosses zero. A solid state relay is an electronic switching device that switches on or off when an external voltage is applied across its control terminals. Ssrs consist of a sensor which responds to an appropriate input a solid state electronic switching device which switches power to the load circuitry and a coupling mechanism to enable the control signal to activate this switch without mechanical parts. Ssrs solid state relays have no movable contacts.

Ssrs are not very different in operation from mechanical relays that have movable contacts. A solid state relay is a non contact switch fully composed of solid state electrical element which can drive high current load with a small control signal. Ssrs however employ semiconductor switching elements such as thyristors triacs diodes and transistors furthermore ssrs employ optical semiconductors called photocouplers to isolate input and output signals. It consists of one input and output terminals.

The relay is equipped with a built in synchronization circuit in order to achieve phase angle control. The output is proportional to the input signal. One is the ac solid state relay and the other is the dc solid state relay. The working of the solid state relays can be understood by categorizing the solid state relays into two categories.