Using Bayesian networks in reliability evaluation for subsea blowout preventer control system

A vehicle accident report system was designed to detect accidents accurately and send message to related person. However, after accident, some components or modules can be damaged and it may cause failure of accident detection. Therefore, Triple Modular Redundancy (TMR) method was implemented in the system to mask faults within the modules and ensure the system to continue working. TMR is one of passive hardware redundancy methods. The system includes three MPU-6050 sensors functioning as vehicle tilt sensors to provide hardware redundancy, a TC9548A module serving as an I2C multiplexer, an Arduino Nano acting as a microcontroller and voter, and a NodeMCU ESP8266 responsible for transmitting message. Based on experiment results, the TMR system has a reliability value of 0.9928, a failure rate value of 0.0004/cycle, and accuracy of 3 sensor value of 85%. While, the non-redundancy system has a reliability value of 0.9286, a failure rate value of 0.0053/cycle, and accuracy of single sensor value of 57%. The results of the system process were sent to and displayed via an e-mail. It can be concluded that the TMR system has better performance than the non-redundancy one.

This research introduces a novel hybrid model for the step-stress accelerated life test in which the stress transitions from a low level to a high level following a certain number of failures or a pre-determined time, whichever comes first. The stress is applied to the triple modular redundancy system, in which each device has a lifetime subjecting to the exponential distribution. This hybrid model significantly reduces testing time under a designated stress level. The test study also examines a simple step-stress testing scenario, concluding based on the type-II censoring scheme. Stress elevation follows the tampered hazard rate model. To estimate the reliability of the triple modular redundancy system and its mean time to failure, point and interval estimates for relevant parameters are determined using maximum likelihood and maximum product of spacings methods. Additionally, optimal timing for raising applied stress is explored, through two different approaches. The effectiveness of estimation methods is examined through the analysis of real-world data and Monte Carlo simulations. While both estimation methods yield convergent results, the maximum likelihood method proves to be more accurate, especially in the case of small sample sizes.

Nanoscale field-programmable gate array (FPGA) circuits are more prone to radiation-induced effects in harsh environments because of their memory-based reconfigurable logic fabric. Consequently, for mission- or safety-critical applications, appropriate fault-tolerance techniques are widely employed. The most commonly applied technique for hardening FPGAs against radiation-induced upsets is triple modular redundancy (TMR). Voting circuits used in TMR implementations are decentralized and consensus is calculated from the redundant outputs off-chip. However, if there are an insufficient number of pins available on the chip carrier, the TMR system must be reduced to an on-chip unprotected simplex system, meaning voters used at those locations become single point of failure. In this paper, we propose a self-checking voting circuit for increased reliability consensus voting on FPGAs. Through fault injection and reliability analyses, we demonstrate that the proposed voter, which utilizes redundant voting copies, is approximately 26% more reliable than an unprotected simplex voter when reliability values of voters over normalized time are averaged.

A Triple Modular Redundant (TMR) system achieves high reliability by replicating data and all processing at three independent nodes. When TMR is used for database processing all nonfaulty computers must execute the same sequence of transactions, and this is ensured by a collection of processes known as schedulers . In this paper we study the implementation of efficient schedulers through analysis of various enhancements such as null transactions and message batching. The schedulers have been implemented in an experimental TMR system and the evaluation results are presented here.

Increasing market pressure for industrial turbine controls that reduce cost of installation, increase availability, and reduce overall installation and commissioning time have driven systems in a new direction. This direction is away from complex and expensive triplex or TMR (Triple Modular Redundant) systems and towards dual redundant and networked control systems. Woodward’s core fuel and combustion control is currently being used in a networked system for GE’s LM2500 aeroderivative gas turbine packages. This networked control system utilizes redundant high-speed communications from the sequencer to fuel control. Packaging I/O is also distributed over redundant communications to localize wiring. The fuel control communicates to the gas metering valves and gas turbine variable geometry servo-valves to reduce wiring and installation time. This control system utilizes simplex CPU’s to save cost and duplex hardware and communications for availability. Expansion of this to full redundant CPU processing capabilities can also be achieved to add availability with some cost tradeoff. Woodward has also applied this full redundancy concept in the commercial marine GE LM2500 package applications. In addition to using network communications the core fuel control system is in itself networked, being “package” mounted. Mounting the fuel control on the package reduces the number of field installation wire terminations and the total length of wire used between the gas turbine and the fuel control. Having the main fuel control system mounted on the package allows the control to be wired and tested at the factory rather than at site. The use of network communications in gas turbine control applications has many advantages. Reduction in overall system cost, installation and commissioning time are the main advantages to using networked controls for gas turbines. System expandability and distributed processing are other advantages. Expanding this with hardware redundancy improves availability.

Design diversity has long been used to protect redundant systems against common-mode failures. The conventional notion of diversity relies on generation of implementations. This concept is qualitative and does not provide a basis to compare the reliabilities of two diverse systems. In this paper, for the first time, we present a metric to quantify diversity among several designs. Based on this metric, we derive analytical reliability models that show a simple relationship between design diversity, system failure rate, and mission time. In addition, we present simulation results to demonstrate the effectiveness of design diversity in Duplex and Triple Modular Redundant (TMR) systems. For independent multiple-module failures, we show that, mere use of different implementations does not always guarantee higher reliability compared to redundant systems with identical implementations-it is important to analyze the reliability of redundant systems using our metric. For common-mode failures and design faults, there is a significant gain in using different implementations-however, as our analysis shows, the gain diminishes as the mission time increases. Our simulation results also demonstrate the usefulness of diversity for enhancing the self-testing properties of redundant systems.

Voting Logic (VL) is an important component of Triple Modular Redundant (TMR) and N-Modular Redundant (NMR) systems. A number of voting logic designs are presented in this paper. The Design Profile, Diagnosability and Reliability calculation of a word voter for TMR system is presented.

The issues of ensuring the reliability of the control system of a biogas plant should be given special attention in the design of the system, in the manufacture of all hardware, in the development of mathematical and software, in the creation of information support, during installation and commissioning, during the technical operation of the system. A research aim is development of measures on providing of operating reliability of the systems of automatic control by biogas plants due to their optimal service. The choice of the optimal strategy allows you to achieve the best results from the operation of biogas plants without attracting additional resources. The importance of the early resumption of the operation of control systems after failures, as well as planning and organizing their effective preventive maintenance, is noted. The need for collection, processing, analysis and use of data on the reliability of control systems is noted. According to the obtained values of failure time and recovery time, the values of the readiness factor for devices of each type and for the control system as a whole are determined. Analysis of the obtained data on failure time, recovery time after failure, readiness factor will allow to develop organizational and technical measures, the implementation of which will increase the operational reliability of the control system of the biogas plant. To assess the reliability, a complex integral indicator is proposed that characterizes the state of normal functioning of the system. Changing the strategy of preventive maintenance and the organization of work to restore the operation of system devices after failures, based on the analysis of the value of the coefficient of normal functioning, it is possible to obtain the necessary values of the reliability of automatic control systems for biogas plants.

The fault‐tolerant technique has been frequently employed to realize a highly reliable computer system. This paper considers the Triple‐Modular Redundancy (TMR) system, which is one of the fault‐tolerant systems whereby the system is partitioned into several blocks and the majority decision is made in each block. The reliability of such a system is evaluated. Based on the relation between the number of partitions and the failure rate of such a system, the following two types of models are assumed:(1) TMR network model, where the failure rate of the whole system increases with the number of partitions, when the failure rate of the block is kept constant.(2) LSI model, where the block failure rate decreases with the number of partitions, when the failure rate of the whole system is kept constant. Especially, in the model (2), the pin‐gate ratio of LSI is taken into consideration. For these models, the expression for the Mean‐Time‐To‐Failure (MTTF), which is the mean operation time until a system failure occurs, is derived. The general tendency of MTTF is analyzed. By numerical examples, the improvement of MTTF by partitioning is demonstrated. The improvement of the TMR system by partitioning is demonstrated quantitatively.

Reliability analysis of subsea blowout preventer control systems subjected to multiple error shocks

The large number of industrial control systems based on PLCs (Programmable Logic Controllers) available at CERN implies a huge number of programs and lines of code. The software quality assurance becomes a key point to ensure the reliability of the control systems. Static code analysis is a relatively easy-to-use, simple way to find potential faults or error-prone parts in the source code. While static code analysis is widely used for general purpose programming languages (e.g. Java, C), this is not the case for PLC program languages. We have analyzed the possibilities and the gains to be expected from applying static analysis to the PLC code used at CERN, based on the UNICOS framework. This paper reports on our experience with the method and the available tools and sketches an outline for future work to make this analysis method practically applicable.

The insertion of communication networks in closed-loop of digital control systems makes the system synthesis and analysis complex. In this paper, we consider the combination of classical reliability, risk and safety evaluation with typical control system through digital networked control systems. The main purpose is to study the influence of transmission delays and packet dropouts on the reliability of digital networked control systems by using a modified statistical method-Monte Carlo simulation. The behaviors of two types of fault are modelled by different statistical distribution. The control strategies we apply for digital control systems are Proportion Integration Differentiation control strategies, generated by Genetic Algorithm. In terms of a realistic system model, we evaluate and compare the influences on the reliability of digital networked control systems with different control strategies from quantitative aspect. Numerical examples are presented to illustrate the effectiveness and correctness of the approach.

Reliability is one of the most critical factors that is to be considered during the designing phase of any product. There are many factors that contribute to make a system more reliable in terms of area, power, operating frequency and accuracy. This paper proposes the design of a 4bit fault tolerant ALU system using backend designing. Parallel processing along with triple modular redundancy (TMR) has been used to increase the operating speed of the system and also to make the system fault tolerant and accurate. The backend designing has been done using Micro-wind 3.1.7

The hunt for increased reliability in systems for critical applications is a never-ending process and is a point of concern for designers in several different fields, such as nuclear reactors. This concern becomes more prominent when a new device technology is integrated into the options for the development of those systems, such as programmable logic devices like the FPGA. With the constant breakthroughs in this technology, there has been an increase in the capacity and the performance of FPGAs. Nevertheless, new methods to keep fault tolerance at an appropriate level for critical applications in hardware must be considered, particularly due to the transient nature of some radiation-induced faults. This work proposes a resilient and adaptable hardware architecture that increases the reliability of circuits implemented in FPGAs, based on a classic active redundancy model, Triple Modular Redundancy with spares. Also, it brings forth a novel hardware architecture that can easily be ported to different FPGA models without compromising performance, reliability, and availability. We discuss and analyze these requirements for the proposed architecture and show that it is more reliable and keeps this reliability for longer periods of time than redundant solutions that use more area.

Field-programmable gate arrays are susceptible to radiation-induced single event upsets. These are commonly dealt with using triple modular redundancy (TMR) and module-based configuration memory error recovery (MER). By triplicating components and voting on their outputs, TMR helps localise configuration memory errors, and by reconfiguring faulty components, MER swiftly corrects them. However, the order in which TMR voters are checked inevitably impacts the overall system reliability. In this study, the authors outline an approach for computing the reliability of TMR–MER systems that consist of finitely many components. They demonstrate that system reliability is improved when the more vulnerable components are checked more frequently than when they are checked in round-robin order. They propose a genetic algorithm for finding a voter checking schedule that maximises the reliability of TMR–MER systems. Results indicate that the mean time to failure (MTTF) of these systems can be increased by up to 400% when variable-rate voter checking (VRVC) is used instead of round robin. They show that VRVC achieves 15–23% increase in MTTF with a 10× reduction in checking frequency to reduce system power. They also found that VRVC detects errors 44% faster on average than round robin.