Safety systems functional diagram

Figure 4-34. Function diagram of the safety systems for emergency and slow shutdowns, and of the speed regulating devices.

Figure 13-3 shows a block diagram of the proposed design for the safety instrumented function of the high line pressure. It consists of two separate and independent shutdown functions in two separate and independent systems (ESDI and ESD2). The components associated with the two systems for this function are ... 

The architecture of the E/E/PES system reahzing the safety-related function is represented basically as a functional safety reliability block diagram (RBD). 

ABSTRACT This paper is focused on the safety analysis of an analogue transceiver located in the BTM, a subsystem of the European Railway Traffic Management System (ERTMS). Balise detection is the transceiver safety related function and the ERTMS specifications define it as a SIL2, setting a maximiun tolerable hazard rate of 10 failures per hour. By means of FTA and FMEA analyses, and failure rate calculation, this paper demonstrates that a bIsT topology is suitable to accomplish safety requirements. The description of the topology and the diagrams of both analyses are also exposed. To conclude, the comparison between the values obtained for both architectures are shown and the safety improvement is e)q)lained. 

A fault propagation method used to analyze failure rate or probability for safety instrumented functions. A diagram is constructed to represent the system under consideration including the logical relationships between its components. In Markov analysis there are a group of circles, each of which represents a system state. The different states are connected with transitions, which are shown as arrows and indicate paths to move from one state to another. The transitions are quantified using either failure rates when the transition is from an acceptable state to a failed state or... 

A further benefit of GSN was realised when it came to asking equipment suppliers for sub-system safety cases. The diagrams showing the breakdown of hazards related to system functions formed an easy starting point for helping each supplier to identify their contributions to the safety case. Various parts of the process argument were also used to show the relationships between different organisations safety activities. 

Figure 1-2 shows the simplified schematic diagram of the SMART nuclear steam supply system (NSSS) and exhibits the safety systems and the primary system as well as auxiliary systems. The engineered safety systems designed to function passively on demand consist of a reactor shutdown system, passive residual heat removal system, emergency core cooling system, safeguard vessel and reactor overpressure protection system. 

The functional concept may be based on the block diagram. All signals are read in with ASIL B and use the dependencies of the system function groups (logical elements) for plausibility checks to implement the decomposition or safety mechanisms. To control the throttle valve and the pressure injection we use current read... 

The EEC standard sets out procedures for managing and implementing a safety life cycle (abbr SLC) of activities in support of a functional safety system. Hence, we can map the various parts of the standard on to our previous diagram of the safety life cycle as shown in the next diagram. 

The arrangement indicated in this diagram allows a small group of sensors to serve a safety system whilst retaining the required safe failure characteristics. For a system such as this to qualify for safety duties it has to be manufactured and tested fully in accordance with the requirements of lEC 61508. It is basically a PES based functional safety system and is similar to the internal bus systems already certified for most safety PLCs. 

The programming language is function block diagram (a limited variability language). Code development and testing is a well known process. Additionally, there are several restrictions for safety function programming which are described in the system safety manual in detail. 

Validation is accomplished during the Functional Development Phase, and it is the determination that the requirements for a product are correct and complete. It can be summarised in the question Are we building the right thing With reference to the left hand side of the V-diagram in Fig. 1.3, Step 2 is all abont validating that the proposed solution (system or item) will indeed meet all the requirements (e.g. safety, contractual, regulatory, derived imposed on it). 

The following diagram (Figure 3) outlines the steps to follow for analyzing and optimizing the functional safety, lEC 61511 (2003), of the system. 

As with all types of system safety analysis techniques discussed in this part of the text (Part II), a complete description of the system, its intended purpose and design functions, as well as any operational flow diagrams must also be evaluated during the performance of an SCA. If the analyst is not entirely familiar with these system characteristics, the subsequent SCA will potential be inaccurate, incomplete, and flawed. 

Software Preliminary Hazard Analysis This type of analysis is used to identify software program routines that are considered to be safety-critical, and thus is conducted prior to software program coding. To perform the analysis, the analyst should make reference to any available system specifications, interface documentation, functional flow diagrams, software flowcharts, storage and file allocation specifications, and any other program descriptive information. 

Using this definition, a block diagram can be drawn to illustrate the system safety function (see figure 9-2). 

Identification of the different barriers against radioactive releases (RRs), for PWRs typically the fuel cladding, the reactor vessel and primary coolant system boundaries and the containment/confinement) Identification of the possible challenges to each of these barriers Definition of a set of plant specific safety functions that are representative of the status/safety margins of each of the barriers Development of a tool — flow diagram, procedure, electronic system — to continuously monitor the status and challenges to each of the safety functions ... 

Y. Oh, J. Yoo, S. Cha, H.S. Son, Software safety analysis of function block diagrams using fault trees. Reliability Engineering and System Safety Elsevier (2005). www.sciencedirect.com. 

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