What are the Advantages & Disadvantages of a Programmable Relay Controller?

Only the simplest powered electrical systems and equipment require just an on-off switch. A programmable relay offers an easy-to-use, low-cost option to add automated control.

Even modern lighting benefits from smart controls. Lighting systems can be automated to stay on for certain periods of time. They can switch on or off on predetermined schedules or be triggered by sensors. Programmable relays also control industrial equipment, building systems and more.

Originally, such control systems would’ve been designed using conventional relays and timers. Later, PLCs (programmable logic controllers) become available. But PLCs are a more expensive option for automation.

Today, programmable relays are another choice available to control electrical systems. Although they are a good fit for many applications, they have their disadvantages too.

Relay Systems Get an Upgrade

Before the invention of programmable relays and PLCs, relay systems contained in cabinets that could be fifty feet long controlled machines. Wires ran in and out of the cabinet to the machine and back. The relays inside clicked and clacked based on the logic defined by the wiring of the system.

When there was an issue or a design change was needed, the change would be drawn out on paper on wiring schematics. The machine being controlled had to be shut down to change wires, add relays, and debug the logic. The amount of labor required for engineers and technicians was extensive.

Engineers knew there had to be a better way. As computers became more popular, engineers developed the design of a standard controller. The goal was to create a system that could be easily maintained and programmed. It had to work in an industrial environment. And it had to be modular so that components could be changed and added. This gave birth to the modern PLC.

Programmable Relays Offer an Alternative

As PLCs advanced, many believed that they would be used in all applications where a relay was once used, but for lower I/O (inputs and output) counts, they were too expensive. But engineers developed another option. Programmable relays combine the benefits of the PLC with less complexity and lower cost. Programmable relays are used in situations where lower I/O points are required.

Programmable relays can be modified faster and easier than their PLC counterparts because they typically function as relays and timers only. Even though PLCs expanded rapidly, programmable relays added more capabilities as well. They are now encroaching upon PLC territory.

A single programmable relay can take the place of many control devices by combining and streamlining controls from multiple pieces of equipment. Smart relays can do many different tasks, like counting, timing, and real-time clock functions. They can automate specific functions including:

  • Industrial machinery (compressor, motor, pump controls)
  • Industrial refrigeration (timers, temperature control)
  • Conveyor systems (stop-go controls, automatic stopping)
  • Industrial level/pressure controls (valve opening/closing)

Each of these applications become more efficient, and easier to manage and to troubleshoot, through the application of Programmable Relays.

Programmable Relay Advantages

Programmable relays are best in simple applications that won’t need to be changed often. Borrowing some design ques from PLCs, programmable relays have several inputs and outputs. They also provide relay, timer, and counter functions in a single unit. Some programmable relays can include over 20 inputs and outputs.

Programmable relays offer a better alternative with lower costs, better performance, and ease of use. They often include a built-in LCD for programming. The LCD is used to display the program, variables, and configuration. Programmable relays also include function keys and buttons to navigate, enter and edit the program, and start and stop the configuration.

Programmable Relay Applications

Manufacturers use more and more programmable relays each year. Some areas where they are used include assembly, pumping, and compressors. They’re also being used in lifts, presses, and material handling. OEMs are pressured with challenges to meet lower costs, smaller product sizes, and offer greater functionality.

Replacing a faulty programmable relay requires a fraction of the time and cost of replacing a PLC. Often programs can be saved externally and loaded to the new relay before the replacement is made.

Building Automation Applications

Low cost and ease of implementation make programmable relays a good fit for the following applications:

  • Lighting controls
  • HVAC controls
  • Security controls
  • Energy management
  • Weather condition controls
  • Air quality controls

Programmable Relay Advantages over Hardwired Controls

The built-in features on programmable relays eliminate the need for separate control devices. Separate timers, counters, and cube relays are no longer needed. Using programmable relays controls OEM costs and minimizes inventory levels and purchasing overhead.

Programmable relays require less space in an enclosure. Being mounted with a standard DIN rail or panel mounting clip requires a smaller mechanical footprint. Smaller controls also mean smaller enclosures, reducing costs even further.

The integrated display shows alarms and input-output status for better troubleshooting. This often eliminates the need for a technician to use a multimeter or logic probe. The implementation of a programmable relay based control system reduces time spent commissioning the system.

Assembling and testing a hardwired system requires a significant amount of time. Wiring, terminal blocks, wire duct, and labor cost are all higher as well. Installation of a programmable relay with its built-in power supply reduces wiring time and testing.

Programmable Relay Advantages over PLCs

Some programmable relays outshine PLCs in real-time control and monitoring. They are, however, most suited to small, stand-alone, low-complexity applications. PLCs also require an additional cost HMI (human machine interface). They also need software to accomplish the same tasks as programmable relays.

Ladder Logic Programming Improves Relays

A PC with proprietary software is often used to program a PLC and some models of smart programmable relays. The most common type of programming used is called ladder logic.

Ladder logic programming uses symbols instead of words to emulate a real-world logic control. The symbols are interconnected by lines to indicate the flow of current through contacts and coils. The number of symbols has increased over the years as functionality has increased.

The completed program has the appearance of a ladder but represents an electrical circuit. The left and right rails of the ladder indicate the positive and ground of the power supply. The rungs of the ladder represent the wiring between the different components.

The completed program is downloaded from the PC to the PLC or smart relay. The computer then runs the program and monitors inputs and outputs. This monitoring of inputs and outputs is one of the most valuable benefits of using programmable relays. Again, you can’t manage what you can’t measure, and programmable relays monitor the key data that makes it possible to manage, troubleshoot and improve performance.

Smart Programmable Relays

Smart programmable relays are used in commercial and industrial automation applications. These include packaging machines, commercial building controls, lighting applications, and more. They’re designed with multiple inputs and outputs, LCD screens, and programming on the device. They make a good replacement for multiple counters, timers, and relays.

Programmable relays are cheaper, simpler, and smaller. They can provide voltage conversion, isolation, and are more reliable. If a PLC isn’t required, programmable relays are a solid alternative. This is good for a few important reasons, the most important one being cost efficiency.

Programmable Relays vs. Micro PLCs

One of the programmable relay’s biggest advantages over PLCs has been cost. But micro PLCs are closing the gap. In many applications, micro PLCs are no more expensive than programmable relays. And they are not difficult to program either. Training is about the same too. Micro PLCs offer the following advantages over programmable relays.

  • Expandability
  • Price/performance ratio
  • Communication options
  • Full-featured operator interface
  • Easier to create advanced programs

Micro PLCs can offer a more scalable solution than programmable relays. This leaves room for expansion. If a machine is upgraded, advanced programming and I/O can easily be added to a micro PLC.

Micro PLCs also offer functions in addition to programmable relay functions, but that were once only available with large PLCs. These functions include math calculations, subroutines, and analog control. Increased memory, alarms and diagnostics come in this smaller package where once only programmable relays could be used. However, programmable relays are easier to specify, and spares are inexpensive and require less stock. Designers should consider the advantages and disadvantages of programmable relays.

Select a Programmable Relay

Relay systems have come a long way since the 1960s when they could span the length of a factory wall. They provide many advantages over PLCs when complex programming isn’t required. As programmable relays improve and add more intelligent controls, they will continue to replace PLCs in more areas.

c3controls Series 900 smart programmable relays offer a wide range of functionality. If you need multiple timers, counters, time switches, auxiliary relays and more, the Series 900 may fit your application.

Remember, programmable relays give you an entire new level of efficiency in terms of monitoring, managing, troubleshooting and improving the performance of your applications. So, why wait? Configure a programmable relay and order at c3controls.com right now.

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