What Is a PLC Controller?

A PLC is a programmable logic controller, or a programmable controller for short, that acts as a tiny computer that helps control an automated system. They’re part of industrial computers that are used in several industries including manufacturing, agriculture, food, and medical/healthcare. The goal is to control machinery with as little manual intervention as possible.

The first PLC was invented for GM in the late 1960s by Dick Morley, a mechanical engineer who founded Modicon/Schneider Automation, Inc). This PLC was a game-changer in the world of automation.

Until the PLC was invented, a hardwired system was used and required careful rewiring and repositioning of relays to meet different needs. It was time-consuming and created too much room for error.

General Motors needed a better way to ramp up production, but they lacked the expertise. They needed an engineer to establish a system that met their needs. Dick Morley’s company Bedford Associations bid on the “Modicon” project and he created the PLC. After his creation proved to be a success, he founded Modicon and soon learned that the PLC was a viable solution to problems many manufacturing and industrial companies faced. The PLC was a hit. As you use a PLC in an industrial setting, they’re designed as solid-state devices with few components. They’re built to withstand excessive use and harsher conditions where there’s more exposure to cold/refrigeration, heat, moisture, dust, etc. Five main components work together within a programmable controller, and you’ll recognize most of them if you have any knowledge of how a computer works.

The central processing unit (CPU) – Interprets data, executes the program, and transmits the output
Communications interface – Receives and transmits the data on networks that come or go from remote PLCs
Input and output interface – Receives and sends data from external/remote devices
Memory – Stores data that the CPU has to run
Power supply – A power source that converts AC voltage to DC

While a home or work computer typically uses Windows, MacOS, or Linux to operate, a PLC usually uses OS-9 or VxWorks. A PLC can be a brick (single box) that fits into one small case. A brick can be expanded. There’s also the modular PLC that fits in a rack and allows for multiple modules that all have different functions.

What Functions Do PLCs Do?

The most common use of a PLC is to act as a relay. It will run scan cycles often to read the input, do what the input is telling it to do, and then complete the output. It starts with input monitoring where the PLC scans the data input and transmits it to the microprocessor. The microprocessor has been programmed by engineers to recognize the criteria provided in the data and use those values to enact the changes laid out in the program. Once the decision-making step of logic programming is complete, the PLC then goes into action controlling switches, motors, relays, and the other devices that make up the system’s output. As an example, in a large warehouse, boxes are sealed and the address is barcoded before going on a conveyor belt. Along the way, a scanner reads the barcode and processes the data to determine if the package is being sent domestically or internationally. It can then direct the box to a chute that opens and directs the package to a conveyor that will continue to international shipments. Another example is something you experience every day. You’re driving down the road and the light up ahead turns red. Before you even stop, a fire truck approaches you from behind and the light turns green just as quickly as it turned red. That’s a PLC at work. PLCs interact with technology first responders have to turn the lights immediately. Or, a pedestrian approaches the street and the lights change to allow the pedestrian to cross, that’s another example of a PLC at work.

Tips for Choosing the Best PLC For Your Company’s Needs

How can you tell what PLC model is best for your needs? Some of the factors to consider are:

Connectivity – Does your system have the appropriate number of input and output ports and are the correct type for the PLC you plan to install?
Electrical capacity – You need to make sure the PLC you choose matches your electrical system’s voltage.
Environmental considerations – How warm or cold is the area where the PLC will be located? If you’re in food processing and run equipment in extreme temperatures, make sure the PLC’s temperature tolerance range is compatible.
Hardware compatibility – The PLC must be compatible with your computer’s machinery and hardware.
Location – Your location can also play a part in the availability of certain models of programmable controllers.
Memory – Do you have enough memory, both RAM and ROM, to run the PLC properly? To run effectively with little trouble, you have to have sufficient RAM and ROM to complete processes.

Your engineering and programming team need to be involved. While PLC programming software uses C programming typically, it may not be the preference of your team. Ladder Logic isn’t for everyone.

PLC and Robotics Go Hand in Hand for Efficiency, Safety, and Speed

The use of robotics in automation manufacturing has taken off. Robots have to be programmed, and you can imagine that would take a lot of time. Mitsubishi realized it didn’t have to be that way while working with Hella Electronics. Visual programming is making it very easy but using drag and drop commands from a tablet PC. PLC code is easily changed to meet the different purposes the robot serves to have the robotic system up and running in minutes.

Programmable Controllers at Mitsubishi Solutions

Mitsubishi Solutions offers programmable controllers for small-scale and stand-alone applications, small-to-medium-scale applications, and medium-to-large-scale applications. MELSEC controllers come in several options and are ideal for:

Automated warehouses and buildings
Automotive industry
Chemical industry
Food and beverage manufacturing
General automation
Injection molding
Inspection machines/scanners
Machine tools

There are modular controllers and one baseless option. Here are a few quick details. Full details are found online in the selection guide.

MELSEC IQ-R: Programmable automation controller with a CC-Link IE embedded CPU with six options for programming languages and 3380 RAM/40M ROM
MELSEC Q: Programmable controller (universal mode) with seven options for programming languages and 1792 RAM/16M ROM and SRAM card/Flash drive option
MELSEC-L: Baseless type programmable controller with five programming language options, 768 RAM/2M ROM

All MELSEC programmable controllers have an operating ambient temperature of 0 to 55ºC, 4,096 input and output ports, and a large selection of network connectivity options. How can Mitsubishi Solutions help you achieve optimal factory automation? Give us a call or reach us online with questions or specific goals that you want to meet. We’ll help you turn your ideas into an actionable plan.