SSRs use electronic circuits to transfer a signal. 

1. The input device (switch) is turned ON.

2. Current flows to the input circuits, the photocoupler operates, and an electric signal is transferred to the trigger circuit in the output circuits.

3. The switching element in the output circuit turns ON.

4. When the switching element turns ON, load current flows and the lamp turns ON
 

5. The input device (switch) is turned OFF.

6. When the photocoupler turns OFF, the trigger circuit in the output circuits turns OFF, which turns OFF the switching element.

7. When the switching element turns OFF, the lamp turns OFF.

• SSRs are relays that use semiconductor switching elements. They use optical semiconductors called photocouplers to isolate input and output signals.
• The photocouplers change electric signals into optical signals and relay the signals through space, thus fully isolating the input and output sections while relaying the signals at high speed.
• SSRs consist of electronic components with no mechanical contacts. Therefore, SSRs have a variety of features that mechanical relays do not incorporate.
• The greatest feature of SSRs is that SSRs do not use switching contacts that will physically wear out

ON/OFF Control

• ON/OFF control is a form of control in which a heater is turned ON and OFF by turning an SSR ON and OFF in response to voltage output signals from a temperature controller. The same kind of control is also possible with an electromagnetic relay, but an SSR must be used to control the heater if it is turned ON and OFF at intervals of a few seconds over a period of several years.
• Low-cost, noiseless operation without maintenance is possible.

Phase Control (Single Phase)

• With phase control, the output is changed every half-cycle in response to the current output signals in the range 4 to 20 mA from a temperature controller. Using this form of control, high-precision temperature control is possible, and is used widely with semiconductor equipment.
• Precise temperature control is possible.
• The heater’s service life is increased.

Optimum Cycle Control

• The basic principle used for optimum cycle control is zero cross-control, which determines the ON/OFF status of each half cycle. A waveform that accurately matches the average output time is output.
• The accuracy of the zero cross function is the same as for conventional zero-cross control. With conventional zero cross control, however, the output remains ON continuously for a specific period of time, whereas with optimum cycle control, the ON/OFF status is determined each cycle to improve output accuracy.
• Many heaters can be controlled using communications.
• Noise-less operation with high-speed response is possible

Cycle Control

• With cycle control (with the G32A-EA), the output voltage is turned ON/OFF at a fixed interval of 0.2s. Control is performed in response to current output from a temperature controller in the range of 4 to 20 mA.
• Noiseless operation with high-speed response is possible.

Precautions for Cycle Control

• With cycle control, an inrush current flows five times every second (because the control cycle is 0.2 s).

• With a transformer load, the following problems may occur due to the large inrush current (approximately 10 times the rated current), and controlling the power at the transformer's primary side may not be possible.

  (1)The SSR may be destroyed if there is not sufficient leeway in the SSR rating.

  (2)The breaker on the load circuit may be tripped.