What is PLC? And what are its uses?
Significant advances in semiconductor technology in the field of microprocessors and high-volume memories made it possible to build programmable electronic logic controllers. In these controllers, unlike controllers based on electromechanical parts, to change the control logic, it is enough to change the control program without changing the wiring or parts. In this case, we can use a programmable logic controller wherever we want.
Advantages of using programmable logic controllers:
1- The use of PLC reduces the volume of control panels.
2- The use of PLC saves a lot of money.
3- PLC does not have mechanical depreciation, so in addition to longer life, it does not need periodic service and repairs.
4- PLC energy consumption is much less than relay circuits.
5- PLC does not create audio and electrical noises.
6- Troubleshooting control circuits with PLC is quick and easy and usually, PLC itself has a troubleshooting program.
PLCs are based on microprocessors, and by having components such as timers, counters, and transfer constants, they make it easy to control complex processes. Each PLC has its programming language, which is the interface between the user and the PLC hardware. The most important programming methods are the ladder method, flowchart method, and sentence list method.
Read more: What is PLC?
LAD ladder programming:
Since all control and logical command maps were prepared and designed as a ladder or something similar before the appearance of PLCs, therefore PLC makers chose this programming method as one of the possible programming methods.
In this method, those ladder elements that perform a specific and complex function or action are displayed with a box for convenience. The instructions written in the ladder method are done from left to right and from top to bottom. It can be said that this language is designed based on the maps of the command circuit.
CSF flowchart programming or FBD function box display:
In this method, the program is written as a block in which each block represents an operator, thus the programs written in the FBD method are a series of boxes that are connected.
This method is usually not very useful independently and is often very useful for troubleshooting or understanding the control logic of the system. This language is designed based on electronic and digital circuits.
Programming using the STL sentence list method:
In this method, every logical operation is written by a suitable sentence or expression. The noteworthy point in this programming method is that each PLC has a unique command code that depends on the type of CPU used. This language is based on computer programming language. The programming language in STL mode is like BASIC or assembly language and is written.
The STL method has much less graphic requirements than the previous two methods, so the type and number of commands that can be understood and executed in this method are more than LAD and FBD methods. For this reason, programs that are written using LAD or FBD methods can usually be converted to STL, while the opposite is not always possible. In STL programming, however many program lines perform a specific action, they are called a segment.
