PLC ladder programming is one of the popular IEC programming languages used in the automation of systems. Learn the basics of how you can program a programmable logic controller using ladder logic programming.
PLC programming is an essential tool for MELSEC series programmable control unit (PLC) lineup. In this tutorial, we are going to look at the basics of programming languages and the main instructions involved. For this tutorial, we are going to use the MELSOFT series GX Works2 as our programming platform.
Figure 1. PLC programming control program. Image used courtesy of the author.
PLC Programming Language in The MELSEC Series Controllers
Some of the basic commonly used PLC programming languages used in the automation of systems include a Ladder diagram (LD), a function block diagram (FBD), an instruction list (IL), and a sequential function chart (SFC).
Ladder Diagram and Instruction List
A ladder diagram is a graphical representation of ladder logic based on electrical circuits. It is made up of rails and rungs forming its main structure and also the rung contact and the rung output that forms the control program.
Figure 2. Ladder Logic Structure. Image used courtesy of the author.
IL on the other hand is the simplest form of programming, that is text-based. The programming languages just note the corresponding PLC address with its condition as either input or output. Consider the ladder logic program below.
Figure 3. Ladder logic program example. Image used courtesy of the author.
The instruction list for the ladder logic program in Figure 3 is shown in the table below where LD represents load contact, ANI represents And Inverse, and OUT represents output instruction.
Table 1. Instruction list.
Getting Started with Programming Languages
Getting started with this tutorial series is a step closer to becoming an expert in PLC programming. Follow this guide, to get started with ladder logic programming and structure.
Happy programming and see you in the next tutorial.
