The importance of diagnostics in the SIS The diagnostics in an Safety Instrumented System (SIS) are of crucial importance because they are the key to reduce the rates of undetected dangerous failures and, therefore, to reduce the probability of failure on demand (PFD / PFH) and increase the SIL. We can see it in the …
The importance of common cause failures When designing a control system, we should paid special attention to common cause failures, that is, to the factors that may cause the simultaneous failure of several components or redundant channels. It is an even more important aspect in the case of safety instrumented systems (SIS) and is considered …
What is a Safety Instrumented Function? The safety instrumented function is a control loop in a process or machine whose objective is safety. SIF is its acronym in English. In the following image we see the most common simplified representation of the SIF. The integrity and performance of the safety instrumented function depends on a …
SIL requirements – Systematic Capability, Failure Probability and Architectural Constraints. The designer of the safety instrumented function must verify that the 3 SIL requirements of the IEC61508 Standard are met. Each requirement will meet a certain maximum SIL level. The final SIL of the SIF will be the lowest of the three and must be …
Phase 7: Isolators and Terminal Blocks In this article we discuss the options we have for isolators, converters, barriers, terminal blocks and other components (index of design phases). 7-Isolators, field terminals and prefabricated cables Converters, Isolators and Barriers They are used to convert signal ranges, to electrically isolate two circuits, to duplicate signals, to amplify …
Phase 6: Power Supply and Circuit Breakers In this article we discuss the design of 24 VDC power supply and circuit breakers (index of design phases). 6-Power Supply and Circuit Breakers The design of the power distribution of the control panel is an important aspect that can greatly influence the availability of the plant. Not …
Phase 5: Selection of HMI In this article we discuss the selection of the HMI / SCADA (index of design phases). 5-Selection of HMI or SCADA In medium or large systems, normally the operator interface is defined in the technical specification. If it is a PLC system we will talk about a SCADA, if it …
Phase 4: CPU selection and Control System Architecture In this article we discuss how to select the CPU and describe the main options for the Control System Architecture (index of design phases). 4-CPU selection and design of Control System Architecture The selection of CPU and PLC / PAC model depends directly on several parameters. Some …
Phase 3: Grouping and segmentation of I/Os and Racks (functional distribution) In this article we discuss the importance of the functional distribution of I/Os, especially in medium size and large control systems (index of design phases). 3-Grouping and segmentation of signals and racks – Functional distribution The way we distribute I/O signals, modules and racks …
Phase 2: Selection of I/O modules (part B) In this article (part B) we discuss other design factors of the selection of Input / Output Modules such as intrinsic safety, electrical isolation, redundant I/Os, etc. (index of design phases) 2B-Hardware selection of input / output modules Link to part A. G) Electrical isolation Normally there …
