Relay controllers are a fundamental piece of equipment that comes in handy in many automation systems. These electronic components are used to control the switching of high-power devices. The most basic relay controllers are known as multi-drop controllers because they can control multiple lights or appliances in the same room. This comprehensive guide provides an overview of its fundamentals, classifications, applications, and general guidelines for selection.

What Is The Meaning Of Relay Controller?

A relay is an electromechanical switch used in multiple applications. It controls a large output power source by making use of a small power source. The said circuit comprises an electromagnet coil and input and output contacts. In the energized state, the coil generates a magnetic field that causes the output contacts to operate, either making or breaking them, depending on the relay nature. A relay lets a low-power circuit switch to a higher-power circuit while they work separately.

Types of Relay Controllers

There are various relay types, and each of them works differently:

Solid-State Relays

SSRs are electronic switches that operate without the use of mechanical moving parts and instead utilize silicon-controlled switches such as transistors. Although SSRs are rated based on their current rating for controlling circuits, they do not possess any moving parts. They turn ON/OFF depending on the input signal, not contact closure. While electromechanical relays are widely used, they are inferior to SSRs in terms of acoustic noise, switching speed, and duration. Some of the typical uses of SSRs include regulating the heating elements that are resistive or inductive.

Thermal Overload Relays

These arm types are used to protect electric motors from overcurrent and overtemperature faults through thermal overload relays. They consist of a bimetallic strip that develops a curve and heats once the current increases beyond the required amount. This bend forms conduits that create contact points in the relay, thereby switching off the motor power. Thermal overload relays keep resetting when the temperature goes down. They are available at cheap prices, making them effective measures in protecting motors from being damaged due to heating.

Contactor

A contactor is a switch that is operational based on an electromagnetic field to control the power circuits. Contactors are of two types – fixed and movable contacts. When a voltage is applied to the electromagnet coil, the magnetic field exerted will attract the movable contact to the fixed contact thereby rendering the switch closed. Contactors are switches used for making or breaking the circuits of motors, heaters, and lights. They perform very well in managing higher power demands.

Electromagnetic Relays

It uses an electrical switch to open or close a circuit. These components offer electrical separation between a control circuit and the switched circuit and are capable of handling higher voltage and current than that a semiconductor could absorb. Electromagnetic relays are commonly used in industrial applications for rapid on-off controls in conjunction with overload protection.

Important Elements and Terminology

Electromechanical relays are used by the relay controllers to regulate contacts and switch or break circuits. By analyzing the fundamental relay, we may determine a few crucial electrical and mechanical components, which are:

• Spring
• Switching Points
• Electromagnet
• Mechanically Movable Contacts

Key Considerations for Choosing Relay Controllers

Features – Figure out how many re­lays the project needs. Equally crucial is conside­ring today’s required bandwidth. But reme­mber, you might need more­ down the line.

Certifications – Determine the­ specific needs, maybe­ it’s HVAC, health care, or food processing, and pick re­lay controllers with the right certifications if ne­cessary.

System inputs – Check if the­ controller you picked can process the input format your control system or sensor trigger use­s. This could be Digital I/O, Analog, RS232/485 Serial, Etherne­t, Modbus TCP, or even Can Bus, among others­. 

Output ratings – Consider about the re­lay’s voltage, current, and power de­aling with the contact material for its specific use­. That helps it perform reliably. For the­ SWOT analysis, pay attention to the safety standards of the­ company and its products. 

Software programmability— It is advised to use programmable relay controllers, where you can write sequences using an integrated tool or platform. 

Relay type— Determine which is more suitable for the application: electromechanical or solid-state relays, relying on power switching, lifetime, turn-on/off time, dimensions, and generated noise. Electromechanical relays are suitable for higher power circuits and make a clicking noise, while solid-state relays are faster and do not produce any sound. 

Environmental resistance— Choose a controller enclosure rating that will allow it to be directly exposed to a wet environment, high temperature, or hazardous area application.

Thus, for the best results, it is essential to select an appropriate relay controller based on its capability to fulfill the intended purpose and requirements. 

Relay Controller Applications

Here are some common applications of relay controllers:

There is a variation of electric motors and heavy power loads, such as those in industrial machinery or heating and ventilation devices.

Where there are dangerous and critical operations, interlocks and fail-safe relay shutdown sequences are required to avoid disasters.

Controlling high-power RF transmitters that are commonly used in broadcast facilities.

Allowing for the control of equipment and processes that are situated far away from the operator.

Switching on and off lighting, alarms, messages, signs, and other systems through time schedules or sensors.

To protect motors and transformers, overload protection should be used, and the capability of automatic resetting should be available.

Flipping from the primary power source and standby power source.

To avoid mixing of microcontroller control and signal with higher voltage or high current load circuits for safety. Stepping up or down the power to control the temperature of electric heating equipment for accurate power control.

Conclusion

Relay controllers for an automation application come in diverse types; therefore, several factors should be considered when choosing and using the proper relay controllers. It is wise to take into account all the aspects regarding your specific system’s loads and control signals to choose the proper relay controller. Having read this, you will be in a better position to use appropriate relay controllers in your circuits.