Safety plays a crucial role in the development of complex computer systems in the relevant areas like railway transport, process industry, power plants, etc. In the design phase of safety-critical systems, various methods are used to make the system work correctly. Due to advancements in technology, safety-critical systems are equipped with the necessary safety precautions but not completely. The malfunctioning of systems may lead to catastrophic accidents. Compared to commonly used safety-analysis approaches like Failure Mode and Effects Analysis, Fault Tree Analysis, Event Tree Analysis, etc., Petri Nets are more suitable for hazard analysis as they can specify data flow and stochastic interdependencies. An example safety-critical system, Railroad Crossing Junction has been modeled using Petri Nets for hazard analysis to detect the occurrences of possible hazards in the system. The proposed modeling framework provides a flexible graphical representation allowing a qualitative analysis based on the safe and unsafe state representations and a quantitative analysis based on the reachability graph that in turn leads to an effective safety analysis. The result of careful and rigorous safety analysis is to identify unsafe states. The results of safety analysis can be used by the designer for re-designing the system to improve safety. The designer of the system needs to repeat the process to detect the unsafe states.
A set of software-safety metrics is presented in this paper. The proposed metrics framework is intended to address software-safety risk assessment and can be used to evaluate the software-safety quality of a process. The framework attempts to assess safety risks from the beginning of the software development lifecycle and helps to implement efficient solutions. The complete framework is based on McCall's Factors, Criteria and Metrics approach and useful for assessing the degree of safety risk prevalence. The objective is to identify software elements that can lead to accidents if not properly addressed with the support of the safety engineering and software engineering disciplines. Various safety analysis methods including hazard analysis, standards, and guidelines are reviewed for their limitations and practical problems are considered. The framework considers measures that contribute to safety assessment through metrics in each of the Software Development Life Cycle phase. An experimental laboratory setup as 'Safety-Critical System' called Railroad Crossing Critical System (RCCS), which implements a safety-critical software, is used for demonstration and to validate the utility of the framework.
This article describes how the field of vision prostheses is currently being developed around the world to restore useful vision for people suffering from retinal degenerative diseases. The vision prosthesis system (VPS) maps visual images to electrical pulses and stimulates the surviving healthy parts in the retina of the eye, i.e. ganglion cells, using electric pulses applied through an electrode array. The retinal neurons send visual information to the brain. This article presents the design of a prototype vision prosthesis system which converts images/video into biphasic electric stimulation pulses for the excitation of electrodes simulated by an LED array. The proposed prototype laboratory model has been developed for the design of flexible high-resolution 1024-electrode VPS, using an embedded computer-based efficient control algorithm for better visual prediction. The prototype design for the VPS is verified visually through a video display on an LCD/LED array. The experimental results of VPS are enumerated for the test objects, such as, palm, human face and large font characters. The results were found to be satisfactory.
Triple Modular Redundancy (TMR) is usually used to increase safety and the reliability of safety-critical systems where three identical segments are used in identical and the ultimate outcome is reached using voting techniques. Fault masking is one of the main techniques to improve the normal actions of a range of safety-critical techniques. Some commercial areas which implement such techniques include process control, transport, and atomic power place and army programs. Integrated Voter for majority and weighted-average used to provide for a fault masking capability in safety-critical systems [1]. The Majority voting gives a high level of safety and the weighted-average offers a good level of availability. If integrated these two gives a good level of safety in Majority voting not in integrated voting. Here propose a new voting algorithm for faulty masking taking the disadvantage of previous algorithm. In this Incorporating Majority voting and score based fuzzy voting schemes. Safety performance is evaluated by running proposed, Majority and score based fuzzy voting on a triple modular redundant (TMR) system for 10000 voting cycles in various error scenarios. Experimental results show that proposed fuzzy Voter is given a higher safety than other two voting algorithms.
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