Power SupplyĪs its name implies, the power supply is the component that keeps the PLC running, delivering 24VDC or 120VAC line voltage in most cases. Let’s review each of these in detail so you understand how the components work together. Though these PLCs are all far from one-size-fits-all, regardless of category, each will include some form of these four components:
These PLCs differ in size, according to the specific applications for which they are suited. Modular PLCs can come in many sizes, with varying levels of power and capability. These PLCs comprise multiple pieces all plugged into a single rack. Due to this design, the manufacturer, rather than the user, will decide the number and types of inputs and outputs. Compact PLCsĪlso known as integrated PLCs, or smart programmable relays, these systems feature a complete system all packed into one small case. Some main classifications include smart programmable relays, compact PLCs, modular PLCs, and small-medium-large PLCs. PLCs come in many sizes and feature different levels of capabilities.
Yet, a PLC is made to function in an industrial environment, controlling concrete inputs and outputs from devices, machines and workers, while a personal computer is built to exist in your home or office. It shares similar terminology with traditional computing systems, including memory, software, CPU, I/O system and more. In this way, a PLC is often described as a small, specialized computer. Without it, the PLC is just an expensive doorstop. Therein lies the importance of user programming, as the program is what causes the PLC to produce the desired results. A PAC uses multiple CPUs in a single system or chassis to provide parallel processing, or specialized processing of different facets of the application. A Programmable Automation Controller, or PAC, may be needed. The scan cycle is measured in milliseconds, more commonly known as “fast.” However, there are some applications where fast isn’t fast enough. This entire process is the “scan cycle.” The larger the number of inputs, the larger the PLC program, the longer the scan cycle.
#BASIC LADDER LOGIC PROGRAM SERIES#
Because PLC’s are in charge of mission critical systems and there are usually people near machines, a series of diagnostics are run to make sure everything is in order, before it scans the inputs again.
Next, it communicates any necessary information to a control network such as Modbus or Ethernet IP. Then, it executes the user programming to enact the desired outputs. Yet, how does this occur?Īs the PLC scans inputs from multiple sources, it scans them and internalizes them. We’ve covered that a PLC relies on a computer processor to turn myriad inputs into logic to control a myriad of outputs. While that is a simple explanation, that is essentially what a PLC does. Now think of thousands or even tens of thousands of circuits all being controlled in coordination with each other. For instance, he can make the light blink on or off or make the light turn off one minute after it turns on. Suddenly, the user can create more complex controls. There is little versatility or flexibility in this application. By flipping the switch, a user can only turn the light on or off. While these might be more sophisticated scenarios, consider the interaction between a simple light switch and a light bulb. As users can program the system in multiple ways to fit a certain scenario, PLCs within many applications across various industries, including conveyor systems, oil refineries, manufacturing lines and more. It controls devices and equipment by connecting different units and enabling them to work in a coordinated manner.Īt the core of every PLC is a basic computer processor that gathers various inputs and evaluates them to achieve the desired output. It’s a specialized, hardened, computer device designed for use within industrial control systems. What is a PLC?īefore we get too far into technical specifics, let’s review how a PLC system operates. Join us as we take an in-depth look at PLC basics, allowing even the non-initiated to understand how the components work and why they’re so important. Versatile and modifiable, these digital computers are essential to many of the systems and devices we rely on today. Programmable Logic Controllers (PLCs) form their backbone, allowing internal components to function together as a seamless unit. Yet, they didn’t get this way on their own! Today’s industrial automation systems are more advanced and tech-savvy than ever before.
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