Relays Operation Principle for Industrial Automation

Relays are foundational components in electrical engineering and automation, playing a critical role in controlling circuits by opening and closing connections.

For industrial engineers and technicians, a firm grasp of how relays operate is essential for optimising processes, ensuring system reliability, and enabling efficient Programmable Logic Controller (PLC) programming.

This article explores the operation principles of relays, their types, and practical applications, shining light on their integral role in modern automation systems.

What Is a Relay?

At its core, a relay is an electrical switch operated by an electromagnet. When current is applied to the relay’s coil, it activates an electromagnetic force, causing its internal contacts to either open or close. This process allows circuits to be controlled without direct manual intervention, offering a reliable mechanism for automation.

The Two Essential Components of a Relay:

1. Electric Contacts 

• These can be main or auxiliary contacts that either open or close to control the flow of current in a connected circuit.

1. Electromagnetic Mechanism 

• This mechanism generates the movement needed to change the state (ON or OFF) of the electric contacts when the relay is energised.

Relays translate electrical logic into mechanical operation. The two states of relay operation, ON (energised) and OFF (de-energised), parallel the concept of digital binary signals (1 and 0). This makes relays perfect for the logic design integral to automation systems.

Simplified Structure of a Relay:

• Coil – Generates the magnetic field when current flows through it.
• Core – A metal structure that concentrates the magnetic field.
• Contacts – Moveable components that establish or break the circuit connection.

Understanding this structure helps engineers address operational issues and configure relays effectively in complex automation systems.

Types of Relay Contacts and Their States

The electric contacts in a relay are classified based on their behaviour during energised and de-energised states:

• Normally Open (NO): The contact remains open (no current flows) when the relay is de-energised, and it closes when the relay is energised.
• Normally Closed (NC): The contact remains closed (current flows) when the relay is de-energised and opens when the relay is energised.

Types of Relays in Automation

Depending on application needs, different types of relays are used. Here’s an overview:

1. Electromagnetic Relays 

  These operate through an electromagnetic field generated by the coil. They are used extensively in automation for their reliability and fast switching capabilities.

2. Solid-State Relays (SSR) 

  SSRs replace moving parts with semiconductors, offering faster operation and greater durability compared to traditional electromagnetic relays.

3. Hybrid Relays 

  Combining the flexibility of electromagnetic relays with the efficiency of SSRs, hybrid relays balance operational performance and durability.

4. Thermal Relays 

  Designed to respond to temperature changes, these are often used for overload protection in motors and other electrical systems.

5. Reed Relays 

  Compact and fast-acting, reed relays are encased in hermetically sealed glass and commonly used in low-current applications.

The Timer Relay – A Vital Component in Time-Dependent Automation Processes

Among the many relay types, timer relays are particularly valuable in industrial applications requiring delays or precise timing. A timer relay combines an electromechanical output relay with a control circuit to determine the delay interval. The two major types are:

On-Delay Timer Relay

The ON-delay timer relay activates its output contacts after a preset time once the coil is energised. This ensures a controlled delay before operation.

Off-Delay Timer Relay

The OFF-delay timer relay immediately switches its output contacts when the coil is de-energised, but they remain active for a preset period before finally switching off.

Example in Action

Imagine you are tasked with creating a circuit where a light bulb turns on 5 seconds after flipping a switch using an ON-delay timer relay. Here’s how it works:

Wiring Solution:

1. Coil Configuration: 

  Connect the relay coil terminals (A1 and A2) to a 240V switch and power supply.

1. Light Bulb Wiring: 

  Wire the live point of the bulb to the normally open contact (14). Connect the bulb’s neutral point to the neutral terminal of the power supply.

1. Relay Contact Setup: 

  Use the normally open contact (NO – 11 & 14). Ensure the timer is set to 5 seconds.

When the switch is flipped, the relay coil energises but delays activating the contacts by 5 seconds. Finally, the light bulb turns on.

This practical example demonstrates how relays integrate with control systems to automate procedures.

The Unique Angle of Relay Applications in Industrial Automation

Relays are not just standalone components but enablers of sophisticated industrial systems. A modern perspective to explore is the integration of relays with IoT (Internet of Things) technologies. This emerging trend is shaping the evolution of relay manufacturing and applications.

IoT-Enabled Intelligent Relays

IoT integration allows relays to:

• Proactively Monitor Conditions 

 Intelligent relays can monitor load currents and environmental factors, sending real-time updates to central monitoring systems.

•  Enable Predictive Maintenance 

 Faults or wear in relay contacts can be flagged through sensor data, enabling timely maintenance and minimising downtime.

• Redefine Remote Control and Automation 

 IoT-relays can be controlled and reconfigured remotely via cloud-connected systems, streamlining operations across geographically distributed facilities.

By understanding these developments, engineers can make informed decisions about future-proofing their automation systems.

Bridging Theory with Industry Practice

To advance your knowledge of relays and automation systems further, explore practical training options and industry mentorship programs. At Greenpeg Academy, we offer hands-on, vendor-neutral training that goes beyond theoretical comprehension, ensuring you can tackle real-world challenges with confidence.