What is the concept of a safety instrument?

In my understanding, there is no such concept as a \"safety instrument\"; only instruments that meet specific requirements constitute a safety instrument system.

The SIS system must be authorized and certified for its safety level (what we refer to as SIL). The design and development process of the SIS system must comply with IEC61508, and it shall undergo functional safety assessment and certification by independent bodies (such as TÜV and BV in Germany) to obtain a certification certificate. It should be emphasized that virtually all well-known SIS systems come with TV certification. Every time I write here, a classmate always criticizes me. He works for an American organization that deals with security system certification; he’s okay. Every time he asks me to mention his organization as well, but I only write about those I truly approve of, and I won’t do anything against my will. Therefore, it is recommended to check the safety certification before using SIS. Keep your eyes open and only recognize authorized certifications. 2. The SIS system must have redundancy. It should employ a multi-redundancy structure to enhance the hardware fault tolerance, ensuring that a single failure does not result in the loss of the SIS system’s safety functions. That’s what we refer to as 2oo3D or 2oo4D, etc. Redundancy must include power supply redundancy, CPU redundancy, card redundancy, etc. 3. The SIS system must have fault tolerance. First is fault containment, which involves restricting the actions of processes to prevent further escalation before errors are detected; second is fault detection, which entails dynamically monitoring information as well as the actions of processes; third is fault recovery, which involves replacing or fixing defective components. 4. Fault safety: When the SIS fails due to internal or external reasons, the protected object (device) should shut down safely in a predetermined sequence and automatically enter a safe state. 5. Fast response speed: The SIS system has excellent real-time performance, and its operating speed is far beyond what a DCS can achieve. 6. Sequential Event Recording (SOE) function: To facilitate better accident analysis and post-event review, SIS systems generally come equipped with a sequential event recording (SOE) function, which allows for the recording, in chronological order, of the times at which various specified input and output values as well as status variables change. The precision of this recording is usually on the order of 1 millisecond. SOEs are very important, as they ensure traceability in the event of an accident. 7. The SIS system is not involved in process control; it only performs interlocking functions. II. Acceptance criteria after the completion of the SIS system: 1. Construction acceptance – Construction acceptance shall be carried out in accordance with the \"Code for Construction and Quality Acceptance of Automation Engineering\" GB 50093-2013. The requirements regarding construction acceptance are clearly specified in this code, and inspections should be conducted in line with those specifications. It is particularly important to pay close attention to the tightening of terminal connections; a loose terminal in the SIS can lead to an accident. It is recommended to use three-level verification (construction workers, technicians, supervisors). 2. SIS hardware acceptance: The hardware requires certificates of security certification, product qualification certificates, software licenses, etc., provided by the system supplier. Acceptance is carried out in accordance with GB/T50770 standards; redundancy tests must be conducted on components such as power supplies, CPUs, and cards – for example, sensors with a three-out-of-two configuration should not be located on the same card – and all these aspects need to be checked. 3. Software testing (interlock acceptance) – Interlock acceptance is also a very critical step; it is necessary to verify whether the programming of the interlock logic matches the design. If there are errors in the interlock logic, the consequences can be severe. During my checks, I found multiple instances of inconsistencies between the logical programming and the design drawings. After the inspection, multiple parties need to sign to confirm it; this is generally a mandatory requirement for safety inspections. 4. Integrity verification: Integrity verification refers to checking whether the SIS system can meet the requirements for eliminating safety risks; it is what is commonly known as the SIL calculation report. Only when both the reliability (PFDavg) and availability (MTTFs) of the interlock system are satisfactory can the interlock circuit be considered qualified. If the SIL verification fails, then the SIS system also fails.

Safety Instrument System – in this context, the word “Instrument” is translated as “instrument”; actually, this word can refer not only to instruments but also to devices, apparatuses, tools, and equipment. Therefore, the original definition of a Safety Instrument System is instruments, devices, tools, and apparatuses that implement safety functions. There is another explanation for safety instruments: such instruments are safe, meaning they possess explosion-proof and fire-resistant features. So, to understand where the term “safety instrument” is used, it is necessary to consider the context.

Please take a look at the fourth floor; I think what he said makes sense as well

This post was last edited by liangtao8309 on 2020-2-18 at 10:40. I think it makes sense for the fourth floor to expand the concept of instruments to include devices, tools, and machinery. Secondly, since safety instruments inherently have explosion-proof and fire-resistant features, isn’t it still necessary to consider the operating environment? For example, if a gauge that is only certified to SIL1 is used in a system intended to reach SIL2 level, and although the gauge itself has fire and explosion protection features, it does not meet the requirements of SIL2, can it still be considered unsafe?

SIS: Safety Instrument System – a safety instrument system; this abbreviation can also mean SIS: Safety Interlock System, that is, a safety interlock system. SIS: Safety Instrument System. A safety instrument system is a safety system viewed from the perspective of instruments; it consists of signaling devices, logical operation devices, and terminal execution devices ； SIS: Safety Interlock System is a safety system that emphasizes functionality; it triggers interlock actions when certain parameters reach safety limits, thereby ensuring safety.