Level Gauge SIL2 Certification System Application Requirements

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SIL certification, also known as functional safety certification, centers around the product's safety functions. Conducting SIL certification is to verify whether this safety function can be reliably and safely implemented.
For instance, with a lighting fixture, we are concerned with its lighting function and whether its light intensity can reliably and safely meet our requirements.

What is the failure rate of SIL certification?
During the SIL certification process, a concept we often refer to is the equipment failure rate, which is a core term in SIL certification. One could say that without determining the failure rate, the SIL certification is incomplete and inadequate. So, what exactly is the concept of the failure rate?
Firstly, to recognize failure rate, we must understand what failure means. According to GB/T 20438.4 and also the definition of IEC 61508, failure is "the termination of a functional unit's ability to perform a required function, or the functional unit operates in a non-required manner." A more intuitive understanding would be: normally, y = f(x), but after failure, it becomes y ≠ f(x), where f() represents the function we预先设定的 (pre-established), and y denotes our safety expectations. This also explains why "function" is the same word for both "function" and "function" in English.
This statement might be too formal and not easily understood by the general public. So, let's use colloquial language to explain, comparing it to a lighting system. When a lighting system doesn't light up or doesn't follow our set requirements, it's considered malfunctioning.
So said, you might know that when a product doesn't function according to our set requirements, we can say it's failed. Then, what's the probability of this failure? That's the failure rate.
After understanding what failure is, we can start to categorize the types of failure. In the concept of functional safety, failures can be divided into two main categories based on their generation causes: systematic failure and random hardware failure. Among them, random hardware failure is quantifiable. The calculation process of PFDavg is based on a probabilistic analysis of random hardware failure.
In the SIL certification process, we analyze the product's theoretical model and utilize empirical data from its market sales to determine the product's failure rate. This information is then integrated with other components of the SIL certification to form a comprehensive system, ensuring reliable and safe execution of the safety function.

The standard for SIL Safety Integrity Level certification primarily includes:
1. IEC61508—Establishes fundamental safety requirements for both the operational and fault prediction capabilities of conventional systems. These requirements encompass general safety management systems, specific product design, and process design to meet safety requirements, aiming to prevent both systematic design failures and random hardware failures.
2. IEC61511 – A functional safety standard specifically for safety instrumented systems in the process industry. It is a domain standard introduced by the International Electrotechnical Commission (IEC) following the foundational functional safety standard IEC61508. In China, the coordinating standard for IEC61511 is GB/T 21109.
3. ISO 13849-1 – Comprehensive safety assessment from components to systems. This standard also provides designers with more quantifiable methods for design implementation.
4. IEC62061 - Standard in the field of electrical systems.
5. IEC61326-3-2 – Additional requirements for immunity levels of safety-related equipment, including low-probability-of-occurrence end conditions at the site.
6. ISO 26262 – Primarily focused on specific electrical devices, electronic equipment, and programmable electronic devices in the automotive industry, dedicated to the automotive sector. It aims to enhance the functional safety of automotive electronics and electrical products.

Safety Integrity Level, abbreviated as SIL, is differentiated by the probability of hazardous failure occurring per hour.
There are four SIL ratings specified in the international IEC standards, with SIL4 indicating high integrity and SIL1 indicating low. Corresponding to each safety integrity level, there are design specifications that can reduce design errors.
The safety level required in the production process is assessed and determined by a specialized production technology company. Generally, for processes with high safety requirements, the required safety level is SIL3.
SIL certification is a third-party evaluation, verification, and certification process based on standards such as IEC 61508 (GB/T 20438), IEC 61511 (GB/T 21109), IEC 61513, IEC 13849-1, IEC 62061, and IEC 61800-5-2, which assess and confirm the Safety Integrity Level (SIL) or Performance Level (PL) of safety equipment. Functional safety certification primarily involves document management (FSM) assessments for the development process of safety equipment, hardware reliability calculations and evaluations, software assessments, environmental testing, and EMC electromagnetic compatibility testing. SIL certification is divided into four levels: SIL1, SIL2, SIL3, and SIL4, encompassing both product and system levels, with SIL4 being the most stringent.