Logic solver systems

Logic solver system Use system manufacturer MTTF data for PFD calculation Use system manufacturer MTTF data for PFD calculation Use system manufacturer MTTF data for PFD calculation... 

Decide on the type of logic solver system that is most suitable for the application bearing in mind the number of safety functions that are needed for the process plant, the complexity of the functions, the technical resources available to the plant and the cost of ownership... 

One advantage of using PES based logic solver systems is that they greatly increase the available decision making power to deal with redundancy options when compared with relay based systems. 

An interlock is a protec tive response initiated on the detection of a process hazard. The interlock system consists of the measurement devices, logic solvers, and final control elements that recognize the hazard and initiate an appropriate response. Most interlocks consist of one or more logic conditions that detect out-of-hmit process conditions and respond by driving the final control elements to the safe states. For example, one must specify that a valve fails open or fails closed. 

House logic-solver components of BPCS, and safety instrumented systems (SIS) in a controlled environment... 

Safety instrumented system (SIS) Any combination of separate and independent devices (sensors, logic solvers, final elements, and support systems) designed and managed to achieve a specified safety integrity level. An SIS may implement one or more safety instrumented functions. 

Remote automatic—based on a sensing element, logic solver, and output signal to close the valve. In most cases, these automatic valves are designed to fail safe. Automatic isolation can be associated with the automatic activation of a shutdown system for equipment or a process unit. 

At PPG, Class 1 Prooftesting also covers 250 Safety Instrumented System loops in the PSM Safety Systems. A Safety Instrumented System (SIS) is composed of sensors, logic solvers, and final control elements for the purpose of taking the process to a safe state when predetermined conditions are violated. SISs are normally controlled by a PLC with the sole function of monitoring a process to insure operation is maintained within the safe operating envelope. 

This International Standard addresses the application of safety instrumented systems for the Process Industries. It also deals with the interface between safety instrumented systems and other safety systems in requiring that a process hazard and risk assessment be carried out. The safety instrumented system includes sensors, logic solvers and final elements. 

The safety instrumented system logic solvers addressed include Electrical (E)/Electronic (E)/ and Programmable Electronic (PE) technology. Where other technologies are used for logic solvers, the basic principles of this standard may also be applied. This standard also addresses the safety instrumented system sensors and final elements regardless of the technology used. This International Standard is process industry specific within the framework of the lEC 61508 series. 

Manual means that are independent of both the SIS logic solver and the BPCS control system may be provided to allow the operator to initiate a shutdown in an emergency. The requirements for manual shutdown are normally defined in the SRS. 

I) Diagnostic displays of the logic solver. These displays show the status of the main processor modules, communication modules, and the I/O modules in the system. Typically, the pass, fail, active status of each module is shown and in many cases, more detailed information about faults in the system is available. 

The hardware, system software and development system of the logic solver is lEC 61508 SIL 3 compliant and has a limited variability language for its application program. 

B.4.4.1 System components pressure sensor configuration, logic solver configuration, final... 

The safety PLC is a certified SIS logic solver per the lEC 61508 series. For a speoifio safety applioation, sensors and final elements are conneoted to the SIS logic solver I/O terminals and the application program is implemented. All safety functionalities referring to failures of the SIS logic solver (for example, online checks, time control) are part of the embedded system. Necessary checks of sensors and final elements are implemented within the applioation software for some functions, approved function blocks exist. 

The SIS logic solver is a PLC, which is specifically designed for safety applications. It is type approved to comply with the lEC 61508 series up to SIL 3. It has input and output interfaces for safety-related process signals and communication with other safety PLC s. It also has interfaces for signals and oommunioation which are not safety-related. The system consists of ... 

This example illustrates how one particular SIS logic solver integrator develops safety application software for its customers. This software is typically developed as a part of an overall system integration process that is discussed in the section below. 

The major safety instrumented system integration services provided with the SIS logic solver consisted of a number of activities including. 

PE logic solvers for SIF applications should provide diagnostics for all elements of the PE logic solver. An IWDT system may provide user selectable options ranging from the shutdown of an input or output card to total shutdown of the system. IWDT diagnostics check items the logic solver manufacturer considers most important. The limitations of an IWDT may include ... 

Transmission of the generated square wave throughout the PE logic solver communication system to improve PE logic solver communication diagnostics. 

The ANSI/ISA-84.00.01-2004 (lEC 61511) standard (Ref. 1) defines a safety instrumented system (SIS) as an "instrumented system used to implement one or more safety instrumented functions. A SIS is composed of any combination of sensor(s), logic solver(s), and final element(s)." lEC 61508 (Ref. 2) does not use the term SIS but instead uses the term "safety-related system." That term defines the same concept but uses language that can be broadly applied to many industries. 

Practitioners often prefer a more functional definition of SIS such as "A SIS is defined as a system composed of sensors, logic solvers and final elements (Figure 2-1) designed for the purpose of ... 

Programmable logic controllers (PLC) often seem a logical choice for safety instrumented system logic solvers. After all, the PLC was designed... 

Can a relay logic system be used to satisfy the requirements for a SIL 3 Safety Instrumented Function What are some of the issues that need to be addressed in using relays as a logic solver ... 

Component failure rate data and PFDavg/MTTFS calculations for two cases of the above system are shown in Table 12-1 and Table 12-3. SFF calculations and architecture limit checks are shown in Table 12-2 and Table 12-4. An assumption was made that a very effective proof test was performed at the specified proof test interval with proof test coverage of 95% for the sensor (full calibration), 90% for the logic solver and 80% for final element (full stroke test). The calculation results and all other results... 

The analog signal comparison can be performed between two or more transmitters that are part of the SIF or between a SIF transmitter and a DCS transmitter (measuring the same process variable). In order to take credit for the comparison it needs to be performed in the SIS logic solver. The software in the Safety Instrumented System is safety critical rated. This is not the case for the DCS software. 

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