Ladder Logic PLC Programming Circuit Branch Example Step 4 - The PLC moves to the rung below.Repeats Step 2 until the rung is completed. Step 3 - The hypothetical current goes to the next instruction.If the XIC is False, the PLC aborts this rung. Step 2 - When the hypothetical current encounters and XIC Instruction, it checks if the condition is TRUE or FALSE.
Step 1 - The hypothetical current starts moving from left to right.If they’re FALSE, the Output Energize instruction will set the bit to 0 (or LOW). Output Energize - This output instruction will set the specified bit to 1 (or HIGH) if the input instruction conditions are TRUE. While the bit is set to 0 (or LOW), the instruction will evaluate to FALSE.
Each instruction has a set of conditions that make it TRUE or FALSE.įor the purpose of this tutorial, we’ll start with two of the most basic instructions in ladder logic plc programming: Examine if Closed and Output Energize.Įxamine If Closed - This input instruction will look at the specified boolean bit and evaluate the condition to TRUE when the bit is set to 1 (or HIGH). The Logic evaluates to TRUE when a hypothetical current is able to pass through the instructions. As the PLC begins to process the rung, it reads the instructions on the left and determines if the Logic on that side of the rung is set to TRUE. 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. Ladder Logic is one of the top 5 most popular types of PLC programming languages used in manufacturing environments.
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