Monday, July 29, 2019

Why you should modernize your Relay Control System with a PLC

If you are still running a hard-wired relay control system, it may be time to consider modernizing with programmable logic controllers, or PLCs. PLCs have gotten smaller and more efficient over the years, and they can replace a complex relay system and provide a host of benefits.


Defining PLCs

A programmable logic controller is what it sounds like - a small, special-use computerized control device used in industrial systems. It handles sequential controls, counters, timers, and more. PLCs are more widely used than special-purpose digital computers and have found a place in industrial manufacturing and civil applications.

A PLC continuously monitors input values from sensors, operator controls, etc. and produces outputs to operate machinery based on programming.

How Does a PLC Work?

A PLC is made up of a CPU module, a power supply, and one or more I/O modules. There is no hard drive since the program is stored in internal memory.  A touch screen or other HMI (Human Machine Interface) is optional. The PLC stays inside a control panel and uncomplainingly does its job.

It performs several steps as part of a typical scan cycle:

  • Cycles the operating system and monitors time
  • Reads data from the input module and checks all input statuses
  • Executes user or application program
  • Performs all internal diagnostics and communication tasks
  • Writes data into the output module

As long as the PLC is on, it repeats the cycle until the programming or process comes to an end.
Programmable Logic Controllers


The Benefits of PLCs

One benefit has already been mentioned. A PLC is used across multiple industries and in smaller machinery. But there are other benefits as well. PLCs are:

  • Robust and durable
  • Easy to program
  • Reliable 
  • Easy to use

The I/O module doesn’t even need to be near the CPU. They can be miles apart and still operate connected by data cables. Your PLC isn’t stuck to a single cabinet or building. A PLC can have more than just digital inputs & relay outputs. Improvements over the years have given PLCs the ability to work with a wide variety of analog signals as well as Ethernet and serial communications protocols.

PLCs give your production lines flexibility that you don't get with relays. If you need to retool your line, you can easily reprogram your PLCs to handle the new process.

PLCs are found in such industries as chemical, automotive, steel, food/beverage and more.

Why you should modernize your Relay Control Systems with a PLC

As you have probably experienced, relays use a ton of electricity. They take up space, and they’re noisy and tend to fail a lot. All those electrical connections between relay & socket & interconnecting wires mean more downtime for maintenance. Mechanical relay systems fail more often than PLCs.

If all you need to do is turn an electrical motor on and off safely, a relay may be all you need. But most industrial processes today involve more than that. You need something modern and smart to make your processes energy-efficient and cost-effective.

Modern industry leverages the power of the computer revolution to improve almost every step of any process. Modernize your relay control systems with a PLC, and you'll wonder why it took you so long.

About the Author:

With over 25 years of experience in the industrial automation repair industry, Jeff Conner is the Dallas Service Manager for Control Concepts and serves on the Advisory Committee for the Electronics Technologies Department at Texas State Technical College.

Control Concepts helps design, fabricate, install, test, and program control systems. They service almost any brand of control found in automated systems and can send an experienced technician anywhere one is needed 24 hours a day, 7 days a week.

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