E. I. Gergely

Design framework for risk mitigation in industrial PLC control

Programmable logic controllers (PLCs) are increasingly used in industrial automation projects. By their nature, in these applications safety is a crucial requirement. However, risk prevention adds costs to the PLC system, which means that a balance between costs and risks have to be found. A convenient compromise between these two criteria is provided by risk mitigation, but only to an acceptable risk level. By reviewing the fundamental definitions and concepts of system safety, and with the support of a simple example, the paper provides a framework for addressing these issues. Exploring the systematic design of safety-critical PLC systems helps to show how design engineers can verify that their projects will be safe.

Approach of PID controller tuning for ball mill

The object of this paper is to investigate the dynamics of the closed loop of a cement mill and to introduce an approach for tunning robust PID controllers. Based on the analyze of the dynamic behavior of the cement mill, a robust PID controller is designed and then simulated. The simulation results confirm that the given approach provides high performances of the cement mill.

Dependability Analysis of PLC I/O Systems Used in Critical Industrial Applications

Programmable logic controllers (PLCs) are widely used in control applications. The growth of control requirements has created new challenges upon PLCs. Dependability attributes, like reliability and safety, became essential parameters in the PLC systems design. Since 90% of the PLC faults belong to its I/O modules, the dependability of the PLCs I/O modules represents a major issue.

A procedure for PLC programs validation

Many control systems involving safety critical operations are presently implemented on programmable logic controllers (PLCs). Therefore, there is a strong need to validate that the considered PLC is compliant with the safety requirements. The paper presents a testing procedure that enables the validation of PLC programs, which greatly reduces the testing effort and provides a close link between overall system safety requirements and the PLC program.

Analysis of two-phase asynchronous motor with non-orthogonal windings in dynamic regime

This paper presents a dynamic regime analysis of the starting and function of the two-phase asynchronous motor with two non-orthogonal stator windings. Simulation results are obtained when the axis of the auxiliary winding is moved with 30 degrees in decreasing and increasing way. The answer concerning optimal choice of the two-phased motor for household applications is given by the results of the dynamic analysis.

Voice command of an industrial robot in a noisy environment

This paper presents a study of voice command in industrial automation. Some tests were conducted on the voice recognition in a noisy environment. Compared to the laboratory environment, the signal was affected by the noise from different sources, such as: electrical motors, machine tools, human operators. An example with noise produced by an induction machine is presented. Finally, some simulation results of voice recognition in a noisy environment are presented.

Dependability analysis of PLC I/O modules

The paper presents a technique for analyzing the dependability of programmable logic controllers (PLCs) I/O modules. The technique is based on the mode in which the I/O modules fulfill their tasks and not on their structure. Such an approach allows a unified analysis of I/O modules, regardless of their type, for almost the entire analysis work. The particularization of the I/O module type becomes necessary only at the final stage of the analysis. There are realized qualitative & quantitative analysis of I/O modules dependability. For this, and because reliability is not an eloquent parameter in any situation, there are defined probabilistical parameters both for one I/O point and for I/O points systems and are made comparisons between some I/O points configurations. Finally there are pointed out several architectures considered optimal and the processes for which they may be suitable.

Method for identifying the environmental noise model for city traffic

This paper presents a method for the estimation of city environmental noise. In this paper is applied the least square method to get the curve that approximates best the samples. Also, it is estimated the environmental noise model using the System Identification Tool from Matlab. The model structure is chosen, next parameters are estimated and then the model is validated.

Coverage influence on the dependability of PLC architectures

The paper illustrates a way of using analytical methods in order to analyze the dependability of several replicated PLC architectures characterized by imperfect coverage. Firstly, we establish the general modeling frame of the dependability and we state the assumptions taken into account for modeling the reliability and safety of PLC systems. Then, the considered architectures are described by the means of block diagrams, functioning mode and associated Markov models. For this purpose three fault coverage factors are considered. The comparative analysis of PLCs architectures dependability is done considering systems safety, reliability and MTTHE, and takes into account several scenarios for the three fault coverage factors. The analysis shows that higher coverage bring consistent improvements in the safety and MTTHE of replicated architectures and constitutes a valuable tool for designers, due to the fact that it shows where and how to interfere in order to improve the overall system dependability.

Assessment of PLC systems dependability by assuming coverage

The paper evaluates the dependability of PLC systems based on assuming the failure modes of the system components. It is introduced a model of the service provided by a system to a single user as a sequence of pairs value-time which has to be recognized by the user. The service model is then improved in order to be applied for the case of a single service provided to multiple users. The formalism used for the failure modes assertions are ordered by the means of an implication graph, where each path represents a more relaxed ordered set of assertions regarding the system behaviour. The probability that a specific assumed failure mode proves to be true in the real system operation can be formalized by the concept of assumed failure mode coverage. Its effects on the system dependability are illustrated by a case study. It is demonstrated that more relaxed assertions made on components failure modes do not necessarily lead to an increase of the PLC system dependability.