Sitting on the train to work, few people would think about the importance of safety and redundancy in their automation systems unless it has been specified as part of a project they are working on. However, Automated Safety Instrumented Systems (SISs) are becoming increasingly common, as they can be used to prevent or mitigate dangerous events in a range of different situations. By placing a process in a safe state when certain conditions are breached, SISs can provide different levels of protection, so it is important to know which Safety Integrity Level (SIL) your intended application needs to meet.
SILs are performance or reliability measures for systems with safety functions. According to the IEC (or EN) 61508 standards for "Functional safety of electrical/electronic/programmable electronic safety related systems" there are four SIL levels. The higher the SIL number, the higher the required protection.
The SIL requirements of a particular application can be determined in different ways. IEC 61508 describes both quantitative and qualitative methods to define which SIL is required. Common approaches are risk graphs or matrices, fault tree analysis or Layer of Protection Analysis.
As the SIL level increases, both system costs and overall system complexity increase. Therefore, the choice to implement high SIL 3 and SIL 4 solutions is not always necessary and the lowest appropriate SIL for the application should be considered.
It should be remembered that the SIL level will ultimately be applied and relates to the total system configuration. The design of the overall system architecture and redundancy at the device level are all factors that influence the SIL classification. It is often the case that a large proportion of systems requiring a SIL level rarely require certification above SIL 2. This of course depends on the application and the risk.
SISs must be fault tolerant
The most important aspect that SIL 2 SISs must address is the continuous monitoring and regulation of relevant machinery, known as "equipment under control", by a safety controller. This helps to prevent risky downtime. As a result, control systems must have redundant CPUs and power supplies, redundant network communication infrastructures and processing units. In this way, in the event of equipment failure, the system can maintain its availability and continue to operate safely.
For example, tunnel ventilation, such as that used in road or rail tunnels, must function when called upon during static traffic conditions or in emergency situations. Redundant control systems provide high availability and instantaneous changeover, which is essential for continuous and safe operation. This can be achieved by means of a patented SIL-compatible PLC platform in combination with a fast and reliable redundant communication network.
Mitsubishi Electric latest SIL 2 certified solution is for example MELSEC iQ-R PLC series, which is characterized by modular structure. Therefore, it can be easily combined with additional CPUs and power modules to ensure system redundancy. In addition, redundant Ethernet communications can be established with one IP address for both control and standby systems.
By choosing Mitsubishi Electric PLCs for SIL 2 applications, users can also benefit from optimum system responsiveness thanks to the high-speed CPUs. Performance across the network can also be improved by using CC-Link IE networking technology, which provides network redundancy and 1 Gbit/s network speeds.
Optimal operational performance is also fundamental. That is why solutions that combine process control and process safety, such as the MELSEC iQ-R for SIL 2, are becoming increasingly popular. These SISs regulate the proper functioning of Equipment Under Control (EUC) by collecting and processing relevant data in both normal and emergency situations. Based on the obtained results, the process and safety controllers communicate with EUC to obtain preset safe conditions.
Furthermore, by choosing Mitsubishi Electric solutions, end users can reduce their total cost of ownership (TCO). The iQ-R PLC series Process Automation Controller (PAC) offers the same level of reliability and functionality typically offered by more expensive Distributed Control Systems (DCS). This is a clear example of how the world of equipment safety is constantly evolving to provide more reliable, available and flexible solutions, so staying up to date is essential for future-proof automation systems.
Are you also curious about the right safety level of your system and what Mitsubishi has for solutions? Please feel free to contact us:
Tel: 0229-714212
Mail info@engineeringshop.nl
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