What Are The Differences Between Solid State Relays And Electromechanical Relays (ssr Vs Emr)?

By Author: huimultd
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The Relay is an electronic control device that acts as an Electric Switch in almost all electrical and electronic equipment. When the input value reaches the set value, the output value will produce a step change in the output circuit, so the relays are typically used to control large output currents with low input currents. And the relays are also used for automatic adjustment (such as temperature control system), circuit protection and circuit switch.

According to the structure, the relays can be divided into mechanical relays (such as electromagnetic relay, electromechanical relay or EMR) and non-contact relays (solid state relay or SSR).

How mechanical relays work

The working principle of the mechanical relay is the principle of electromagnetic induction. The structure of mechanical relay is very classic and has hardly changed since its invention, and consists of two parts: the coil and the contact.

Solid-state relay diagram
Click here to know more information about the solid state relays

With the development of science and technology, the demand for relays (small size, long service ...
... life, high stability, high performance, and high compatibility) is increasing, so the semiconductor components are used as the switching components in the relay. There are no mechanical contact and coil in such relays, which is different with the traditional mechanical relays.

§2. Why choose Solid State Relays

ADVANTAGES

Electromagnetic Relay

Solid State Relay

AC and DC compatible Anti-vibration, anti-shock
Can provide multiple sets of contacts; normally open and normally closed contacts are both available Anti-corrosion and moisture proof
Cheap price Asynchronous & synchronous switching mode
Compact size Compatible with digital circuits
Low residual voltage Fast response time
No heat sink required Low control power, usually 10-50 mW
No leakage current Long life, 50-100 times
longer than electromagnetic relays

Low electromagnetic interference(EMI) in synchronous switch mode

No mechanical strain

No mechanical moving parts

No noisy action

DISADVANTAGES

Electromagnetic Relay
Solid State Relay
Contact bounce Leakage current
High control power. Usually higher than 200mW Not suitable for small output signals
Limited contact life Only a single contact
Maximum switching frequency is limited (5-10mhz) Output can only be AC or DC, not compatible
Noisy action Residual voltage 1-1.6V
Need interface for the digital loop Usually need a heat sink
Poor working ability for large currents, will produce electric arc
Produce electromagnetic interference (EMI) during operation
Switch action cannot be fully synchronized

The above table helps to compare the advantages and disadvantages of SSR and EMR, and it can be found that the characteristics of SSR and EMR are different due to different structures. However, in actual application, the advantages of solid state relay are very obvious, and due to the excellent advantages as follows, which is the reason why use solid state relays, and why Solid State Relays gradually replace the Electromechanical Relays in many fields.