The basic concepts of Programmable Logic Controllers (PLCs) are relatively simple, but they are extremely important to understand in order to effectively operate, program, and debug PLCs. PLCs are a type of computer used to control machines and processes.
What makes up a PLC?
A PLC consists of three main parts:
1. The processor: The processor is responsible for controlling the overall operation of the PLC.
2. The memory: The memory stores the instructions and programs used to control the PLC.
3. The input/output (I/O) interface: The input/output interface is used to connect the PLC to outside devices and sensors, allowing the PLC to receive input from and send output to the external devices.
What is the logic of PLC
PLCs also run on logic, meaning that all operations are based on logical decisions. This logic is implemented by the use of Boolean algebra, which defines true and false conditions and how operations are performed based on the results of these conditions.
PLCs are programmed using a variety of logic programming languages including Ladder Logic, FBD (Function Block Diagram) and IL (Instruction List). Ladder Logic is the most common programming language used to program a PLC, and it uses a graphical logic representation to create a program. In Ladder Logic, the logic functions are represented by rungs of logic or relay-type logic and are connected together in a ladder-like fashion. FBD and IL programming languages are also available and use a more traditional programming syntax, similar to that of a text-based programming language.
What languages does PLC speak?
Finally, PLCs are programmed using a special language, either ladder logic or a similar language. This language is used to create the instructions and programs that the PLC uses to control the external devices, as well as any logic used in the operations.
PLCs use a variety of programming languages to control their functions. The five most popular PLC programming languages are as follows:
1. Ladder Diagram: Ladder Diagram is a graphical type of language that was originally modeled from relay-logic schematics. Ladder logic is the most popular language for PLC programming due to its simplicity, modularity, and resilience.
2. Sequential Function Charts: Sequential Function Charts uses steps and transitions to achieve your end results. Sequential Function Chart is the easiest to implement, and can be used to break large processes into major steps
3. Function Block Diagram: Function Block Diagram describes a function between inputs and outputs that are connected in blocks by connection lines. Function Block Diagram is easier to read and conceptualize, but can become messy and unorganized.
4. Structured Text: Structured Text is a textual based language that is like Basic, Pascal, and “C”. Structured Text is best used for control systems that require mathematics or complex tasks. It is a very powerful tool that can execute complex tasks utilizing algorithms and mathematical functions along with repetitive tasks. Each line of code must be written and it uses functions such as FOR, WHILE, IF, ELSE, ELSEIF AND CASE. Experience with Basic or C languages will enable programmers to find this PLC Programming Language easier than some of the other types of PLC languages.
5. Instruction List: Instruction List is very straight-forward to read and can be used for complex projects, but can be trickier to debug and resolve errors.
Summing up
PLCs are capable of monitoring many processes at once, and can be programmed to respond to specific inputs. For example, the programming of a PLC could be used to detect if the temperature of a system exceeds a certain threshold and then trigger a reaction to bring the temperature back to the desired level.
PLCs can also be used to create a feedback loop. This is when the input of the system is continuously monitored and adjusted in order to maintain a predetermined result. An example of this would be a car assembly line where sensors are used to detect when an assembly has been completed and then the machine is instructed to move on to the next one.
Overall, Programmable Logic Controllers are highly versatile devices that can be used in a variety of applications, from controlling industrial processes to creating feedback loops. They are used to improve the accuracy and efficiency of various tasks, and to help maintain safety protocols for industrial settings.