PLC
PLC (programmable logic controller). It is an electronic equipment designed for use in industrial environment, has programmable memory for storage of instructions. The instructions are defined by logic, timing, counting and arithmetic, to control through analog inputs and outputs, various types of machines and processes.
Where is the PLC used?
Any and all processes that you want to automate. Integrating applications using temperature sensors, pressure controllers, pneumatic and mechanical actuators. Avoiding excessive use of external equipment such as contactors, timers, drives and temperature controllers.
Benefits
- Process reliability.
- Industrial Security.
- Low Maintenance.
- Ease of future projets changes.
- It has several models, with different features.
Disadvantages
- Need for qualified professionals.
- Acquisition cost.
PLC Programming Language
In order to serve the largest number of users and the most applications, the publication IEC 61131-3 defined the syntax and the semantics of five programming languages (FRANCHI; CAMARGO, 2009), as shown below:
- Ladder LD: Graphical language based on the logic of relays and electrical contacts, used to create control and drive circuits. It is present in the vast majority of current PLC models.
- List of Instructions IL: Inspired by assembly language and purely sequential. Because it is extremely limited, it is currently not used in machine and equipment programming.
- Graphical Sequencing of Functions SFC : Graphical programming language that allows the development of sequential, parallel and alternative actions existing in industrial applications. The language SFC has been successfully used in large sequential applications in the process industry.
- Structured Text ST: High-level textual language and very powerfull. By encompassing all the essential elements of a modern programming language, how conditional statements (IFTHEN-ELSE e CASE OF) and repeat instructions as (FOR; WHILE e REPEAT), this language is widely used to control complex processes that require structured programming.
- Function Block Diagram FBD : Graphical programming language widely used in Europe, in which the logical elements are expressed by interconnected blocks. This language allows a modular development of the software, very important feature for the control of continuous processes present in the chemical, oil and food industries, among others. Usually the blocks are created using the Structured Text language.
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