PLCs: The Workhorse of Industrial Automation

What is a PLC?

To successfully automate the manufacturing of anything in today’s world depends greatly on the ability of different industrial systems, both mechanical and electrical, to communicate with each other quickly and efficiently. This used to be accomplished through the use of large and cumbersome relay banks that consisted of hundreds and sometimes thousands of individual electrical relays, all wired together in specific configurations. Today, the same tasks that used to be completed by those relay banks are now accomplished using just a fraction of the space, set up time, and electricity using programmable logic controllers or PLCs.

With the trend of automation becoming more and more embedded in all aspects of manufacturing, PLCs are truly essential. The workhorse of industrial automation, PLCs are small, special-purpose computers with no display, keyboard, printer, or hard drive. Its purpose is to control specific manufacturing outputs using unique inputs and preprogrammed rules. You will find these unique computers hiding in the control panel on almost every factory floor where even the smallest amount of automation is needed.

What makes up a PLC?

Three main components make up a PLC. The first two components consist of an input module and an output module that combined make up the I/O inputs. These are linked together by the CPU or central processing unit. This is the computer and central component of the PLC. Let’s take a more in-depth look at each main component as well as some of the ancillary parts of the PLC that are important to keep in mind when choosing which PLC is the right fit for your application.

Industrial Control Panel

1 – Input Module (i.e., field sensors) – These are the physical connections between the outside world and the PLC. These sensors sense when an external signal is received and convert that signal into an electrical signal that is then sent to the accompanying CPU to be processed. Sensors come in two variations, digital or analog. Digital sensors only provide information on whether something is on or off. Some examples of digital sensors include on/off switches, bimetallic strips, float switches, etc. To collect information that varies between on and off, an analog input is needed. Some examples of an analog sensor include a control knob, thermocouple, pressure sensor, strain gauge, etc

2 – Central Processing Unit (CPU)This is the “brains” of the PLC that holds the software with the preprogrammed rules, that decide what outputs are exercised given the signals received from the input module. It consists of a microprocessor to perform the logic task, a memory chip for storage, and other integrated circuits.

3 – Output Modules (i.e. field output devices)These are downstream devices that receive a specific signal from the CPU to execute a preprogrammed response action. Some examples include variable frequency drives, indicator lights, motors, starters, etc.

4 – HMIs and Network ConnectionsThese components, usually found in the CPU of a PLC allow a user to interact with and monitor the PLC. HMIs, or the Human Machine Interfaces, are screens that allow for some direct configuration or programming of the CPU by a user. They are also often used to display I/O readings to a user so operations can be easily monitored. Network connections on the other hand are integrated circuits such as Ethernet or Modbus that also allow a user to remotely interact with the CPU.

PLCs have helped to revolutionize automation and have made machine operations more efficient and effective to program, perform, expand capabilities, troubleshoot, and repair manufacturing devices in a multitude of industries. MISUMI can help you build the exact PLC system for your company’s needs. Feel free to contact electrical@misumiusa.com to speak with an electrical professional today.

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