Relays are basically considered as an electrically operated switch. It is composed of electromagnetic, an armature, a spring and a set of electrical contacts which electromechanically or electronically open and close the circuits. It actually controls one electrical circuit by opening and closing contacts in another circuit.
What makes SSR different from an EMR?
Solid State Relay (SSR) is a non-contact switch made up of electronic solid state components. It enables the connection, disconnection and sparking circuits without contact based on electronically components including switching transistors, triacs and other semiconductive components. Electromechanical relays (EMR) are also widely used in industrial applications.
Differences between solid state relays (SSR) and electromagnetic relays (EMR):
EMR is a magnetic switch consisting of spindles, moving elements, contact system and also have mechanical motion inside.
In comparison, SSR is an electronic switching system consisting of thyristor, silicon controlled rectifier (SCR), high-power transistor and are without inside mechanical movement elements, optically separated between input and output.
EMR regulates the on-off state of circuits by electromagnetic force, based on the principle of electromagnetic induction.
Whereas SSR achieves isolation and relays switching on/off functions based on the electrical, magnetic and optical properties of semiconductor and electronic components.
Compared with SSR, EMR reacts very slowly, creates some noise and also has a short time span. SSR responds very quickly; it does not generate noise and has a long life span.
EMR operating environment is not quite as strong as SSR.
SSR has a strong operating environment and perfect for rust, humidity, dust, high altitudes, electromagnetic interference and other harsh environments.
EMR is a simple drive, have good isolation and tolerance for short-term overload, but high energy consumption while SSR produces no electrical spark and has no contact. They have fast speeds for high current control through a small control signal.
Electromechanical relays offer various advantages.
In many applications, SSRs have replaced EMRs, but it is still quite common in many industrial applications.
Nonetheless, in some applications, SSR also has some limitations which restrict its use.
An electromechanical relay uses a moving physical part to connect contacts within the relay’s output portion. This contact will be driven by electromagnetic forces from the low power input signal so that the circuit with the high-power signal is completed.
Solid State relays use semiconductors to work without the need for contact. SSR produces the optical semiconductor, usually with an optocoupler, which transmits and energizes the output signal with a low power electrical message. Once activated, the optical input signal acts as a switch allowing a high voltage signal to pass through the output portion of the SSR. There are many ways to do that, but the key element is the absence of moving parts, thus making it solid-state.
The following chart explains various terminologies used in EMR and SSR. A very handy guide.