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.
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.
You can also read:
- The Basics of Instrumentation and Control Systems
- The Transition from Relays to PLC systems Explained
- How to Integrate a PLC into your Control System
Don't miss out on key updates, join our newsletter list here.
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.
