Relays, as fundamental components of electronic control systems, bridge the control system and the controlled system through electromagnetic effects. They enable automated control and protection in circuits. A thorough understanding of their principles, features, and applications provides valuable insight into their indispensable role in electrical systems.

Below are the 8 essential relay types that every seasoned electrician should be familiar with:

1. Intermediate Relay

Intermediate relays are specialized electromagnetic switches that use the magnetic field generated by a powered coil to attract an iron core, thereby controlling the closure or opening of contacts. Their multi-contact design caters to controlling multiple circuits, enhancing flexibility and efficiency in circuit control.
Applications: Used in logic control systems, signal amplification, and circuit isolation.

2. Solid-State Relay (SSR)

Solid-state relays utilize semiconductor devices such as transistors or thyristors to control circuit on/off states. They achieve electrical isolation between input and output via optocouplers and are capable of directly driving high-current loads. Their high-speed and precision control make them ideal for:

· Robotics

· Lighting systems

· EV charging stations

· Solar power generation systems

3. Pulse Relay

Pulse relays are designed to handle pulse signals, performing opening and closing actions within extremely short time frames. They can be either electromagnetic or solid-state. Solid-state pulse relays (SSRs) use semiconductors, eliminating mechanical contact and offering longer lifespan and faster switching speeds.
Applications: Timing circuits, high-speed switching operations, and digital control systems.

4. Safety Relay

Safety relays combine multiple relays and circuits to achieve robust safety functions with minimal error. They ensure protection for operators from machinery-related risks. Upon receiving safety inputs, these relays process the signals through internal circuits to deterministically output control signals for equipment safety circuits.
Applications: Machinery safety systems, emergency stop circuits, and safety interlocks.

5. Overvoltage Relay

Overvoltage relays are electrical protection devices that monitor input voltage levels. When the voltage exceeds a preset threshold, the relay activates to disconnect or control the output circuit, thereby protecting it from overvoltage damage.
Applications: Voltage regulation in power systems, equipment protection, and fault prevention.

6. Time Relay

Time relays utilize electromagnetic or mechanical principles to delay the closing or opening of contacts. Typically used in applications requiring time-based motor startup control, they begin timing upon receiving a start signal and activate contacts after the set delay.
Features: Adjustable delay settings, providing flexibility in timing configurations.
Applications: Sequential circuit control, motor start delay systems, and industrial automation.

7. Liquid Level Relay

Liquid level relays monitor and control the height of liquids in containers. Using floats or sensors, they detect changes in liquid levels. When the liquid reaches a predefined level, the relay triggers the corresponding circuit to perform control actions.
Applications: Managing liquid levels in water tanks, pools, and oil reservoirs.

8. Pressure Relay

Pressure relays monitor and control the pressure of gases or liquids. They use pressure sensors to detect changes and trigger circuits when the pressure reaches a preset value.
Applications: Pneumatic systems, hydraulic systems, and pressure protection in industrial equipment.

Conclusion

These relays play a critical role in PLC automation and control systems, ensuring safe, reliable, and efficient circuit operation. Understanding their features and application scenarios is vital for improving electrician skills and ensuring the stable operation of electrical systems.

Whether you're troubleshooting equipment, designing systems, or maintaining infrastructure, mastering these relay types enhances your ability to handle a broad range of electrical challenges.