Simple Plc Programs Examples
If you’ve been wanting to get into industrial automation and been looking for basic PLC training, but you are not sure where to start, then this Beginner’s Free PLC Training blog series has been written for you!After you’ve read this 4-part free PLC training series you should be able to identify the primary components of a PLC system and have a basic understanding of the purpose and function of PLCs (and PACs).When you complete this series, you should be ready to begin learning PLC programming. If you have any questions about this content, please feel free to comment on the post or email me directly at. So, without further delay, let’s jump right into our introduction to PLCs!Beginner’s Free PLC Training Series Outline. Introduction to PLCs.Programmable Logic Controllers (PLCs) are small industrial computers with modular components designed to automate customized control processes. PLCs are often used in factories and industrial plants to control motors, pumps, lights, fans, circuit breakers and other machinery. To understand the purpose of PLCs better, let’s look at a brief history of PLCs.
HistoryIndustrial automation began long before PLCs. In the early to mid 1900s, automation was usually done using complicated electromechanical relay circuits. However, the amount of relays, wires and space needed to create even simple automation was problematic.
Thousands of relays could be necessary to automate a simple factory process! And if something in the logical circuit needed to be changed? Oh boy!NOTE: On a basic level, electromechanical relays function by magnetically opening or closing their electrical contacts when the coil of the relay is energized. The are very useful devices and still play a major role in industrial automation (for a more in-depth lesson on electromechanical relays check out this ).In 1968 the first programmable logic controller came along to replace complicated relay circuitry in industrial plants. The PLC was designed to be easily programmable by plant engineers and technicians that were already familiar with relay logic and control schematics. Since the beginning PLCs have been programmable using ladder logic which was designed to mimic control circuit schematics. The ladder diagrams look like control circuits where power is flowing from left to right through closed contacts to energize a relay coil.Ladder Logic ExampleAs you can see, ladder logic looks like simple control circuit schematics where input sources like switches, push-buttons, proximity sensors, etc are shown on the left and output sources are shown on the right.
Plc Application Examples
The ability to program complicated automated processes with an intuitive interface like ladder logic made the transition from relay logic to PLCs much simpler for many in the industry.Although, the first PLCs were very limited in their memory and speed capabilities, they quickly improved over the years. The presence of PLCs helped simplify the design and implementation of industrial automation. For more on the history of PLCs, see this great little article from AutomationDirect. How Do PLCs Work?PLCs can be described as small industrial computers with modular components designed to automate control processes.
PLCs are the controllers behind almost all modern industrial automation. There are many components to a PLC, but most of them can be put in the following three categories:. Processor (CPU).
Siemens Plc Ladder Logic Examples
Inputs. OutputsPLCs are complex and powerful computers. But, we can describe the function of a PLC in simple terms. The PLC takes inputs, performs logic on the inputs in the CPU and then turns on or off outputs based on that logic.
We will get into more detail later but for now, think of it like this:. The CPU monitors the status of the inputs (ex. Switch on, proximity sensor off, valve 40% open, etc.). The CPU takes the information that it gets from the inputs, performs logic on the inputs. The CPU operates the outputs logic (ex. Turn off motor, open valve, etc.)See the flowchart below for a visual representation of the steps above.PLC Function FlowchartLet’s use a familiar example to illustrate how PLCs work.
Plc Programming Examples Traffic Light
Your dishwasher. Many dishwashers have microprocessors that function similarly to PLCs. The dishwasher has inputs, outputs and, of course, a CPU.
Some of the inputs into the dishwasher controller would be the buttons on the front, the water sensors and the door switch. Some of the dishwasher outputs would be the water valves, the heat elements and the pumps. Now let’s think about how the dishwasher uses those different components.NOTE: Remember, the CPU is the processor in the dishwasher that is programmed to make all the decisions we will see below. Thanks for the comment, Don! Interesting perspective.
Out of curiosity, in what specific ways do you think the PLC is easier to maintain and troubleshoot for the laymen/electrician? I have always found the PAC to be easier to use and program in every aspect. Most of my peers seem to agree. IT also appears that the market agrees to some extent, in light of Allen-Bradley retiring their PLCs? I’m interested to hear why some people find PLCs to be easier to troubleshoot/maintain? Thanks again for your interest.
Hi Ron,Sounds like your bad experience with PACs is possibly due to a lack of documentation/drawings on the part of the original programmer (IT guy?)?I find that Allen-Bradley PACs are just as easy and often easier than PLCs to troubleshoot. For instance, if an I/O module or rack is not responding, you can easily see which one has problem by simply looking at the left side in the controller organizer and looking for the module with an error.
There’s also a simple light that tells if all the I/O is OK or not. Little things like that really help!Is there any specific ways that you find PLCs to be easier to troubleshoot than PACs?Thanks for your comment and interest, Ron.SDG.