Selecting instrumentation for functional safety (SIL) applications

For more than five decades FCI has been a world leading manufacturer of sensors and instrumentation solutions for industrial processes and plant operations, on-board aircraft and nuclear power plants applications. For each of these segments, FCI offers an array of products with superior performance and quality, longest service life and with the pedigrees and certifications that meet or exceed the industry norms and the application conditions.

Over the past couple of decades, the process industries have seen many changes when it comes to the design and implementation of emergency shutdown and safety systems. The introduction of several international and regional standards requires a more rigorous approach to the overall safety lifecycle of a system compared to the use of best engineering design practices of the past. As a result, a broader and significant increase in the implementation of these standards has been noted within the industry.

The standards most commonly being referenced by users are:

• IEC 61511: Functional Safety — Safety Instrumented Systems for the Process Industry Sector
• ANSI/ISA-84.00.01 (IEC 61511 Mod) — Functional Safety: Safety Instrumented Systems for the Process Industry Sector
• IEC 61508: Functional Safety of Electrical, Electronic, Programmable Electronic Safety Related Systems
   

The industry segments that appear to be driving the most demand at this time are chemical, petroleum refining and oil and gas. FCI is seeing more requests for SIL ratings when it comes to thermal mass flow meters, flow switches and level switches. FCI has responded and today provides more SIL-compliant thermal dispersion technology products than any other supplier.

SIL (Safety Integrity Level) is just one piece of data required to meet the requirements of these standards but it continues to be the initial focus of inquiries. Reliable failure rate data is just as critical when it comes to evaluating the impact an individual sensor will have on the overall Safety Instrumented System (SIS) design and validating that particular Safety Instrumented Function (SIF), being used to calculate Safe Failure Fraction (SFF) of a product, evaluate required Hardware Fault Tolerance (HFT) and allowing a design engineer to perform PFDavg calculations. To ensure that FCI provides unbiased failure rate data, we utilise independent, authorised third parties such as exida and TÜV Nord to perform the FMEDA (Failure Modes, Effects and Diagnostics Analysis) per IEC 61508 for several of our thermal meters and thermal switches.

One thing that tends to get lost in this focus on standards is whether or not the instrument selected will actually be able to perform the desired safety function. Ideally, the instrument selected will comply with the relevant safety standard as well as perform the necessary measurement. However, it is hard to justify the selection of an instrument that has a strong pedigree but will not bring the system to a safe state when a demand is placed upon it. In those cases, it may be best to fall back on a proven-in-use approach based on site experience with a particular instrument in an application.

FCI’s thermal mass flow meters and thermal flow/level switches have been used extensively within the process industries as safety instruments, helping customers limit the risks associated with potentially hazardous processes. As the implementation of newer standards related to safety instrumented systems continues to increase, customers can continue to rely upon FCI to meet their instrumentation requirements and provide them with the proven benefits associated with thermal flow meters and thermal flow switches.

Please contact AMS Instrumentation & Calibration for more information on how FCI can meet your present safety instrumented system requirements.