In this paper the authors study a Safety Instrumented system (SIS) subjected to periodically performed diagnostic measures or tests. They focus their interest onto partial tests similar to partial stroke tests, which ...
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ISBN:
(纸本)9781479904297
In this paper the authors study a Safety Instrumented system (SIS) subjected to periodically performed diagnostic measures or tests. They focus their interest onto partial tests similar to partial stroke tests, which are well known from testing valves. They then introduce diagnostic parameters in order to quantify manual, automatic and semi-automatic testing mathematically, and they distinguish between two different diagnostic modes: The semi-automatic component-based mode and the semi-automatic-time-based mode. In Chapter V, they investigate the semi-automatic mode by means of two functions depending on their diagnostic parameters: The diagnostic coverage factor and the cost function. They then pose two optimization problems in form of two linear programs. The first one minimizes the cost function under constraints on the diagnostic coverage, and the second one maximizes the diagnostic coverage under constraints on the cost function. The paper closes with the examples of a 1oo1-system and a 2oo2-system.
This paper deals with finding optimal structures and redundant safety designs with minimal costs for series-Parallel multi state system (MSS) configurations subject to availability constraints using genetic algorithms...
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ISBN:
(纸本)9781629935881
This paper deals with finding optimal structures and redundant safety designs with minimal costs for series-Parallel multi state system (MSS) configurations subject to availability constraints using genetic algorithms as optimisation mean, since these biologically inspired evolution concepts showed stability, powerfulness, and effectiveness in solving such complex combinatorial optimisation tasks. The routine has been written in Matlab and the tests have been performed using some test data belonging to already existing models (Levitin, Lisnianski, and Ouzineb).
The approach for calculating the failure rate of a safety integrated circuit is used if the number of available test patterns is not sufficient. The safety integrated circuit can be structured in function blocks, that...
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ISBN:
(纸本)9781479904297
The approach for calculating the failure rate of a safety integrated circuit is used if the number of available test patterns is not sufficient. The safety integrated circuit can be structured in function blocks, that can be functionally compared to semiconductors with discrete structure. Failure models already known and applied for discrete semiconductors can be used to determine the failure rate of the individual function blocks. These models with their known failure rates serve as a reference for the safety integrated circuit function blocks. An advantage of this approach is that the internal safety integrated circuit structure can be taken into consideration when calculating the failure probability. The paper is based on the principles of the generic standard IEC 61508 Edition 2, 2010-04. Because new technologies lack field experience and a basis for evaluating certain risks, a conservative approach to determining failure rates has been emphasized as set forth in SN 29500.
Maintenance starts with reliable diagnostics. programming Logic Controllers (PLCs) are often equipped with a high degree of diagnostic procedures in order to ensure that the processing unit is functioning correctly. I...
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ISBN:
(纸本)9781629935881
Maintenance starts with reliable diagnostics. programming Logic Controllers (PLCs) are often equipped with a high degree of diagnostic procedures in order to ensure that the processing unit is functioning correctly. It is vital to verify that the system with its programme is still within a 'healthy' state, otherwise a safety function is called and the system is brought into a safe state, or if possible, defect and malfunctioning components are exchanged during operation and the process can continue without shutting down the system. However, when it comes to smaller devices such as intelligent sensors, embedded controller devices with the functionality of an e.g. PID (Proportional-Integral-Derivative), predictive controller, filter or analytical algorithm, which is embedded into a FPGA or micro-controller then diagnostics and verification methods are often not considered in the way they should be. For example, if an intelligent sensor system is not able to diagnose that the sensor-head is malfunctioning, but the sensor-head still provides some data, then the smart algorithm bases its calculation on wrong data, which can cause a dangerous situation. This paper investigates and shows recent results to combine diagnostic methods for small scale devices. Several safety-related structures are considered with a high degree of diagnostic coverage. The paper presents relevant procedures and structures to increase the reliability of small devices without utilising a full scale microcontroller system.
Sensor communication applications not only require high performance processing but also flexible and reliable computing. Today, standard microprocessor systems are still application oriented and aren't suitable by...
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This paper deals with achieving safe wireless communication for safety related systems with Bluetooth technology. In industries at present safe communication between the field bus/devices, PLC/controllers, and system/...
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ISBN:
(纸本)9781622764365
This paper deals with achieving safe wireless communication for safety related systems with Bluetooth technology. In industries at present safe communication between the field bus/devices, PLC/controllers, and system/applications (SCADA, DCS and MES systems) is achieved using safe wired industrial communication protocols such as safe field buses or safe Ethernet. To achieve safe communication, there are certain safety methods, these methods are discussed in the European standard document EN 50159-2. Wired industrial communication protocols implement these methods to achieve safe communication. To determine safety, mathematical equations are derived, which are suitable for wired communication, and which takes into account only the bit errors present in the transmission channel. As there are both bit errors and erasures (loss of information) present in the wireless channel, the mathematical equations derived for wired communication should also take into account erasure of information for wireless communication. This paper derives the mathematical equations for wireless communication to determine the safety and with the implemented safety methods for Bluetooth technology;safety integrity level SIL3 achieved is shown.
This scientific work presents a new method allowing to make a realistic prediction about software-reliability of critical systems. The main feature of this method enables the prediction of an estimate of the remaining...
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ISBN:
(纸本)9781622764365
This scientific work presents a new method allowing to make a realistic prediction about software-reliability of critical systems. The main feature of this method enables the prediction of an estimate of the remaining critical number of faults in the software. The algorithm uses already known methods such as Imperfect Debugging. This method can provide an even more reliable prognosis than the conventional methods. Furthermore, the new method describes two processes for critical failures (detection and correction process). The new algorithm considers a time, which is called repair-time. This time is important for the reliably prognosis and it is mathematically described as a time-function and used in the prediction model. The software reliability models (SRM's) are used since the 70's, these software reliability models are based on stochastic and aiming to predict the reliability for the software and also for the hardware. SRM's are based on model assumptions, some of which cannot be applied anymore. Thus, for the reliability engineering today, these models are insufficient.
In Functional Safety it is necessary to calculate safety parameters in order to determine the safety integrity level as well as to determine PFD and MTTF values. Nowadays, several international valid safety standards ...
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ISBN:
(纸本)9781622764365
In Functional Safety it is necessary to calculate safety parameters in order to determine the safety integrity level as well as to determine PFD and MTTF values. Nowadays, several international valid safety standards exist for different user and application areas. In every standard different methods and procedures occur to calculate relevant safety parameters and to determine the failure rates of the components. Those are often only partially comparable. Today, different tools exist to calculate safety loops. However, the models to calculate the parameters are often unknown to the user and therefore it is difficult to state the quality of the solution. This paper discusses these problems and presents a tool, which calculates according the IEC 61508 Ed. 2 standard. This tool is developed in cooperation with a database established by TUV Rheinland, and will give users an advantage in calculating appropriate and reliable parameters.
The present paper deals with the quantitative analysis of the safety-related systems. The configuration of such safety-related system is composed of channels that include both detectable and undetectable failures. It ...
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ISBN:
(纸本)9781622764365
The present paper deals with the quantitative analysis of the safety-related systems. The configuration of such safety-related system is composed of channels that include both detectable and undetectable failures. It also deals with a possible calculating model of a safety-intrusion and their consequences on the safety-related system, but it is also important to note at this point that information and experimental results for this model with real data are not (public) available yet. This model should clearly demonstrate the possible calculation of safety-intrusion model, based on high reliable architecture, with the help of Markov models.
Let there be given a safety related electronic system suffering from random failures or errors. The standard IEC 61508 contains simplified equations for the probability of failure on demand PFDavg for special system a...
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ISBN:
(纸本)9781622764365
Let there be given a safety related electronic system suffering from random failures or errors. The standard IEC 61508 contains simplified equations for the probability of failure on demand PFDavg for special systemarchitectures, mostly without proof. In various publications PFDavg is defined by several different equations, e.g. as a Laplacian probability, as an integral mean, or by means of the average failure rate of the system. The aim of the paper is to determine PFDavgby stochastic methods and to bring together the different definitions. A formula for PFDavg is given that is valid for most universal electronic systems. The equivalence of 2 different definitions of PFDavgis shown. The special case of a koon-system is investigated, and the resulting equations improve those known so far. The basic idea is to randomize the time to failure, the down time of the system, as well as the repair time, and then, by means of the Stieltjes-Integral, determine the mean or average time as the expectation of the respective random variable.
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