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Sequential Function Charts
Published in Murat Uzam, PIC16F1847 Microcontroller-Based Programmable Logic Controller, 2020
The IEC 61131-3 standard defines two graphical languages, namely ladder diagrams (LD) and function block diagram (FBD), and two text-based languages, namely instruction list (IL) and structured text (ST), for use in PLC programming. The graphical languages use symbols to program control instructions, while the text-based languages use character strings to program instructions. The IEC 61131-3 standard includes an additional programming framework called sequential function charts (SFC). Sometimes SFC is categorized as an IEC 61131-3 language, but it is actually an organizational structure that coordinates the standard’s four true programming languages, i.e., LD, FBD, IL, and ST. The SFC structure is much like a flowchart-type of programming framework, utilizing different languages for different control tasks and also routing control program actions [R5.1].
Programmable Logic Controller (PLC)
Published in Chanchal Dey, Sunit Kumar Sen, Industrial Automation Technologies, 2020
At the early stage of PLC programming there was no standard. Manufacturers used to develop their own programming techniques and hence users faced difficulties if they intended to change their existing PLC programs. To overcome this limitation, an international standard was adopted in December 1993 by International Electrotechnical Commission (IEC). At present, this standard is defined as IEC 61131-3, which deals with basic software architecture and programming languages of the control program for PLC. It defines two graphical and two textual programming language standards:Ladder diagram – graphicalFunction block diagram – graphicalStructured text – textualInstruction list – textual (deprecated in 3rd edition of the standard)Sequential function chart – graphical and textual. It has elements to organize programs for sequential and parallel control processing.
Basic Programming Principles of PLCs
Published in Stamatios Manesis, George Nikolakopoulos, Introduction to Industrial Automation, 2018
Stamatios Manesis, George Nikolakopoulos
The standards that are generally created by international associations and committees play an important role in the development of all industrial technologies. The standards generally help in achieving compatibility, transparency, and interoperability across different products; increase users’ confidence in their products; and help in developing tools and methodologies under a common umbrella of technological specifications. Thus, the IEC came to address the chaotic situation in the incompatibility of programming languages for PLCs with the establishment of the open standard IEC 61131, the first part of which was issued in 1992 and referred to PLCs in general. The third part of this standard, the so-called IEC 61131-3, was issued in 2003 (second edition) and referred to the programming languages of PLCs. Nowadays, all major PLC manufacturers have accepted this standard, and their products are developed accordingly. It must be noted that the IEC 61131-3 standard, by definition, is not an additional programming language; instead, it supports modern software engineering methods in order to lead PLC operation in improved languages and programs, creation of usable and interoperable code, and in easy debugging.
An overview of current technologies and emerging trends in factory automation
Published in International Journal of Production Research, 2019
Mariagrazia Dotoli, Alexander Fay, Marek Miśkowicz, Carla Seatzu
The implementation of distributed and decentralised control algorithms in factory automation and in particular in process industries has been realised through different generations of technologies (Yang, Vyatkin, and Pang 2014). The distributed automation concept application began a few decades ago with the development of fieldbuses to collect data from spatially distributed sensors, actuators and local regulators and process them centrally by a centralised control unit in PLCs (Vyatkin 2011; Yang, Vyatkin, and Pang 2014). Later on, with the increasing demand for flexibility in production, there has been a substantial drift towards so-called ‘intelligent mechatronics components’. Such components are individually equipped with embedded controllers (Yang, Vyatkin, and Pang 2014). Embedded systems applications are growing, and the corresponding need to network several embedded systems to perform complex task arises, resulting in sensor networks and wireless sensor networks (Chen et al. 2010). Combining the decentralised/distributed control logic with the sensor networks concept results in a new approach to automation that is often referred to as distributed intelligence, in which a decentralised/distributed control hardware architecture is implemented with multiple controllers in charge of individual mechatronic devices (Yang, Vyatkin, and Pang 2014). To cope with this concept also in the control logic, loosely coupled PLCs are interconnected via networks and middleware or over the Ethernet, e.g. initially by the PROFInet-CBA standard and later by the Modbus-IDA protocol (Vyatkin 2011; Yang, Vyatkin, and Pang 2014). Another possible approach is to develop a software architecture that is inherently distributed, e.g. distributing software across several concurrently running PLCs: however, the current IEC 61131-3 standard still lacks guidelines to convert transparently modular organisation of automation software to virtually and physically distributed configurations (Vyatkin 2011; Yang, Vyatkin, and Pang 2014). Hence, the International Electrotechnical Commission has addressed these issues in the IEC 61499 standard (Vyatkin 2011). The main concept of the IEC 61499 standard is an event-driven module called Function Block (FB). Using FBs, this standard establishes a reference architecture for the implementation of distributed control algorithms at an industrial level, providing the adequate complementary notation and architecture to the PLC programming architecture of the IEC 61131-3 standard. Here we just summarise the numerous research works on IEC 61499 into three categories (Yang, Vyatkin, and Pang 2014): 1) contributions on the implementation of such a standard; 2) works proving the benefits of the use of such a standard by comparison with alternative solutions; 3) papers updating the standard with concepts from the computer science area. Some detailed state of the art surveys on the IEC 61499 related research may be found in (Thramboulidis 2006; Vyatkin 2011; Vyatkin 2013).