The PLC executes the program loaded into it one rung at a time. A boolean takes a single bit in the memory, can be set to 0 or 1, and is used in most basic PLC instructions. In the programming world, this data type is called a boolean. Just like computers, PLCs operate with binary signals each one can be set to zero or one. In this post, we will go over ladder logic components, cover basic principles, and outline what it takes to master this programming language. Learning ladder logic is typically the entry point into a career in control systems as a PLC programmer. It’s easy to learn, mimics electrical circuits, and is easy to troubleshoot once deployed. Each rung of the ladder spans from left to right and is executed from top to bottom by the PLC.Īs mentioned above, ladder logic is extremely popular among PLC programmers. On the left side, ladder logic instructions are set as conditions, while the ones on the right side are instructions that are triggered if the conditions are met. Ladder Logic is labeled as such because the software is laid out in the shape of a ladder. As PLCs took over this process, it was essential to keep a similarity of the old system thus, ladder logic was created as the first PLC programming language. Relays were costly, required constant maintenance, and could not be easily reconfigured. Before Programmable Logic Controllers, manufacturing plants employed relay-based circuitry to energize different loads based on how the relays were wired together. The result of this type of connection will result in a short circuit.Ladder Logic is one of the top 5 most popular types of PLC programming languages used in manufacturing environments. Control devices are never to be connected from the left rail to the right rail. Control devices are connected between the left side of the rail and the load or other control devices and the load. The load is the last component connected to the right side of the rail unless there is a protective contact that opens the circuit in the case of an overload event. The loads in a ladder diagram are always and shall be connected in parallel on the rungs. Read the ladder diagram from left to right then up to down in order to understand the sequence of the operation. The rungs are the horizontal lines that illustrate how the control devices and loads are interconnected to make up the control circuit.ġ.A ladder diagram translates similarly to a book. The control circuit voltage is usually rated at 12V-120V depending on the rated values of the loads connected in the circuit. The rails are the two dark vertical lines that represent the power source to the control circuit. The ladder diagram, shown in figure 4, is easy to read since there are only two basic parts- the rails and the rungs. Ladder diagrams however, often show multiple lines leading to and from components whether they are series or parallel connections. A one line diagram has only one line between individual components. Ladder diagrams should not be confused with a one-line diagram. Lines between the symbols can be horizontal or vertical but should be drawn to minimize lines from crossing each other. The circuit should indicate the most direct path of logical sequence. Graphic symbols, abbreviations, and device designations are drawn per industry standards. The arrangement of symbols in ladder diagram should promote clarity and understanding. Ladder diagrams provide a fast and easy understanding of the connection of electrical components in a circuit or operation. A ladder diagram, shown in figure 3, is a diagram that explains the logic of the electrical circuit or system using standard NEMA or IEC symbols.Ī ladder diagram is used to point out relationships between circuit components, not the actual location of the components.
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