Oytun Eris

Design of signal control structures using formal methods for railway interlocking systems

Today the relay based railway interlocking systems are changing into programmable software interlocking systems. Looking at the hardware aspect, safety certified components can be used in order to satisfy the safety requirements of railway interlocking systems. But to satisfy the software requirements, the design and the programming of the interlocking system must be made by formal methods. To do this, preparing function blocks for each kind of the field equipments can be a method in order to realize a railway interlocking system. The purpose of this paper is to develop a Programmable Logic Controller (PLC) program for the signal function blocks by using formal methods and make a comparison between them.

A new PI tuning rule for first order plus dead-time systems

This paper presents a new PI tuning method for first order systems with a long dead time. The PI tuning rule is aimed to be simple so that it would be easy to design and apply the controller to industrial processes. The proposed tuning rule is found by z-domain design techniques, in order to get the fastest response without overshoot. The results obtained by the proposed method have been compared with other tuning rules like Ziegler-Nichols and Cohen-Coon, which are frequently used in actual practice. In addition to this, experimental results obtained by using the proposed PI tuning rule are also given.

A new voting strategy in Diverse programming for railway interlocking systems

The main issue in controlling systems such as nuclear power reactors or railway systems is to provide safety at the highest level where risk ratio is high and sometimes small errors might result with death of several people. In order to improve reliability and keep safety of such systems at the required level by decreasing common cause failures at the same time Diverse programming (which is synonymous with N-version programming) technique can be used. In this study an example railway interlocking architecture is explained and a new voting strategy is also proposed.

Use of non-identical multiple delayed resonators in active suspension systems of railway vehicles

In this study, an active suspension system with multiple non-identical delayed resonators (DR) is proposed in order to, suppress vibrations that are caused by railway track irregularities. Mathematical models for a railway vehicle and track irregularities are given. In addition to this, methods on choosing the physical parameters and the design steps of multiple DR are mentioned. Simulations using the approximate mechanical parameters of a Shinkansen SKS300 train are made. Results and comparison with other methods are also given to evaluate the success of the proposed method.

N-version Programming for Railway Interlocking Systems: Synchronization and Voting Strategy

Abstract The main issue in controlling safety-critical systems such as nuclear power reactors or railway signalization systems where risk ratio is at the highest level because small errors might result in hazardous accidents (e.g. death or injury of several people) is to satisfy safety-related standards and provide high-safety with high-reliability. In order to improve reliability and safety of such systems to the required level by decreasing common-cause failures at the same time, diverse programming (or N-version programming) technique where N-different independently designed modules run in parallel on the same input output specifications can be used. In this study, a new bitwise voting strategy based on safe-states of variables is proposed and possible critical races between modules those run in a parallel manner are determined. Solutions for critical races are also explained.

A New Delayed Resonator Design Approach for Extended Operable Frequency Range

The operable frequency range of the Delayed Resonators (DR) is known to be narrow due to stability issues. This study presents a novel approach for DR design with a combined feedback strategy that consists of a delayed velocity and non-delayed position feedback to extend the operable frequency range of the DR method. The non-delayed position feedback is used to alter the natural frequency of the DR artificially while delayed velocity feedback is employed to tune the frequency of DR matching with the undesired vibrations. The proposed method also introduces an optimization parameter that provides freedom for the designer to obtain fast vibration suppression while improving the stability range of the DR. An 1 Corresponding Author * The author conducted this research in part while he was with Control and Automation Eng. Dept., Istanbul Technical University.

A new approach for the design of relay control circuits

Nowadays, the use of electronic control units are limited in applications that require high safety integrity. Therefore, to satisfy the conditions for applications requiring high reliability, control circuits are used instead of digital electronic control units like PLCs. Due to the lack of efficient, simple and applicable methods in the literature, design of control circuits are mainly based on heuristic methods. In this study, existing problems related to the application of the known formal methods will be examined and an effective solution will be proposed.

Comparison of the Parallel and Serial Architectures for N-Version Programming as Applied to Railway Interlocking Systems

Abstract The concept of functional safety gains importance with the increasing number of hazardous accidents in the railway industry. In literature, some hardware and software architectures are proposed for the functional safety. As N-version programming is getting popular as preferred software architecture in railway industry, the effect of various hardware implementations of N-version programming on the functional safety remains unclear. In this study, two different hardware setups will be evaluated for N-version programming. After the effect of these hardware setups on the functional safety is analyzed, the effects on the hardware usage and overall response time will be tested on a sample train station.

Safety-Critical Interlocking Software Development Process for Fixed-Block Signalization Systems

Abstract Reliability is defined as “ability of an item to perform a required function under given conditions for a given period of time” in CENELEC (European Committee for Electrotechnical Standardization) EN 50128 document where software development requirements for railway applications are defined. Similarly, Software Reliability is defined as the probability of failure-free software operation for a specified period of time in a specified environment which is also important factor affecting system reliability (Pan, 2012). Systems such as railway signalization systems, where small errors can result in fatal accidents and death of several people or possibility of unwanted risks (like component malfunction) is high, also need software with high reliability. In this study, some parts of the safety-critical interlocking software development process for the Turkish National Railway Signalization Project (TNRSP) executed in cooperation with Istanbul Technical University (ITU) and The Scientific and Technological Research Council of Turkey (TUBITAK) for Turkish State Railways is defined.