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Programmable Logic Controllers are industrial digital computers used as automation controllers in manufacturing processes. The Ladder language is a programming language used to develop software for such controllers. In this work, we consider the description of the expected behaviour of a Ladder program under the form of a timing chart, describing a...
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... Статья [24] посвящена дедуктивной верификации программ, написанных на языке LD из стандарта IEC 61131-3. Темпоральные требования к LD-программам задаются с помощью временных диаграмм. ...
Process-oriented programming is an approach to developing control software in which a program is defined as a set of interacting processes. PoST is a process-oriented language, which is an extension of the ST language from the IEC 61131-3 standard. In the field of control software development, formal verification plays an important role due to the need to ensure high reliability of such software. Deductive verification is a formal verification method in which a program and its requirements are represented as logical formulas, and logical inference is used to prove that the program satisfies the requirements. Control software often has temporal requirements. We formalize such requirements for process-oriented programs as control loop invariants. However, control loop invariants that represent requirements are not sufficient to prove the correctness of the program. Therefore, we add extra invariants containing auxiliary information. This paper considers the problem of automating deductive verification of process-oriented programs. An approach is proposed in which temporal requirements are specified using requirement patterns which are constructed from basic patterns. For each requirement pattern, a corresponding extra invariant pattern and lemmas are defined. In this paper, the proposed approach and schemes of basic and derived requirement patterns are described. The schemes of basic extra invariant patterns, schemes of lemmas defined for basic patterns, and a set of basic patterns and lemmas for them are considered. The scheme of derived extra invariant patterns and schemes of lemmas defined for derived patterns are defined. The algorithms for constructing derived extra invariant patterns and lemmas for them, as well as methods for proving these lemmas are presented. The schemes of proving verification conditions are considered. The proposed approach is demonstrated with an example. The analysis of related works has also been carried out.
... Ladder diagram features constitute an active research area. Verification of ladder program properties has been considered in [4,5]. Work [4] proposed an approach based on theorem proving. ...
... It presents how to map ladder diagram program fragments to algebraic expressions and means of manipulating them to prove program properties. The theorem proving is further analyzed in [5], which presents ...
This paper presents a modern method of detecting unstable states in ladder programs. Ladder programs are standard formalism used in a wide range of automation applications, especially in railway signaling systems. This formalism is characterized by a lack of explicit program control flow, which can result in the presence of unstable states. A state is unstable, if it leads to cyclic state transitions not anticipated by the designer (loop). The presence of unstable states is one of the possible program defects. This kind of defect is hard to detect and can harm program reliability. The presence of unstable states can be verified with formal methods by the construction of a ladder program model and analysis of its properties. The authors propose a method of static analysis of ladder programs by translating them into predicate logic formulas and construction of formulas expression stability of the program, which can be analyzed with SAT solvers. The presented method allows for automatic verification of the presence of unstable states in the program. The method is conservative (i.e., it concludes that the program has no unstable states only if it is the case). Preliminary experiments performed by authors with a Z3 solver indicate that the method is suitable for use for verification of interlocking programs of computer-based railway signaling systems.
... The programming of the PLC is carried out using the Ladder language [11][12][13] (Fig. 4) with serial/parallel connections and the defined variables. ...
The purpose of this study is to perform the monitoring of the automated belt conveyor transportation process using SCADA technology as well as to obtain the necessary skills for applying SCADA in case of other processes. Modern modelling and simulation methods were used, in order to analyse the results of the control simulation of multi-motor drives. This was done simultaneously with the optimization of the parameters of the automation model, then resorting to the analysis and synthesis of the Ladder program for command and control, correlated with the SCADA software. The method of modelling, simulation and software development for the middle layer of a belt transport flow is described. The practical application of modelling, simulation and software development and testing on the experimental plat-form is presented. The originality of the study results from the fact that it is carried out on the principal structure of the process, the automation strategy, respectively the specific requirements of the automatic control. The experimental test platform is hardware-in-the-loop. Monitoring is done using a series of software monitors written using SCADA software for remote monitoring and control. Practical implications of this work are that, based on this template, additional implementations would more easily be found, for instance by using future versions of SCADA with newer hardware and with additional monitoring system, for instance to develop applications such as transport belts and passenger transport bands in airports.
... In the remainder of this Introduction to the special issue, we briefly present the contributions of the papers that make up this special issue. The paper Automated Formal Analysis of Temporal Properties of Ladder Programs, by Belo Lourenço et al. [5], the recipient of the FMICS 2021 Best Paper Award, describes a new approach for verifying the code running on programmable logic controllers (PLCs). PLCs are industrial digital computers used as automation controllers in manufacturing processes. ...
... In the future, Belo Lourenço et al. [5] would like to improve the counterexample generation of their tool and augment the trust in translation from ladder logic to WhyML by developing a systematic and automatic validation process. Hansen et al. [19] plan to formalize the FMI 3.0 standard, integrate the Scenario-Verifier with other orchestration engines, and examine whether it is possible to synthesize an optimal orchestration algorithm for a given co-simulation scenario. ...
Formal methods and tools have become well established and widely applied to ensure the correctness of fundamental components of industrial critical systems in domains like railways, avionics and automotive. In this Introduction to the special issue, we outline a number of recent achievements concerning the use of formal methods and tools for the specification and verification of critical systems from a variety of industrial domains. These achievements are represented by four properly revised and extended versions of papers that were selected from the 26th International Conference on Formal Methods for Industrial Critical Systems (FMICS 2021).
