Programming languages for many industrial devices are limited by design. Not all programmable logic controllers support all five language types, but nearly all of them support the Ladder Diagram (LD), which will be the primary focus of this book. The IEC 61131-3 standard specifies five distinct forms of programming language for industrial controllers:

If you are learning to program a particular PLC that does not exactly conform to the IEC 61131-3 standard, you will still be able to apply every single principle discussed in this chapter – the fundamental concepts are truly that universal. After learning how to program one model of PLC, it is quite easy to adapt to programming other makes and models of PLC. C/C++, BASIC, FORTRAN, Pascal, Java, Ada, etc.) than between the programming languages supported by different PLCs, and this fact does not prevent computer programmers from being “multilingual.” I have personally written and/or analyzed programs for over a half-dozen different manufacturers of PLCs (Allen-Bradley, Siemens, Square D, Koyo, Fanuc, Moore Products APACS and QUADLOG, and Modicon), with multiple PLC models within most of those brands, and I can tell you the differences in programming conventions are largely insignificant. There exist much greater disparities between different general-purpose programming languages (e.g. One should take solace in the fact that despite differences in the details of PLC programming from one manufacturer to another and from one model to another, the basic principles are largely the same. This is the IEC 61131-3 standard, which will be the standard presented in this chapter.

Although it seems each model of PLC has its own idiosyncratic standard for programming, there does exist an international standard for controller programming that most PLC manufacturers at least attempt to conform to.

Allen bradley ladder logic program