Understanding MTTF Values in Safety Sensor Applications: An Inquiry about B10 and Operational Metrics

The frequency at which you test the transistor output is less significant than the actual usage frequency, as the wear on the transistor for your specific application is minimal and likely hard to quantify. The primary reason for failure is more likely to stem from voltage fluctuations, which are not related to wear and tear. If you were operating in the megahertz range for switching cycles, it would make sense to consider wear; however, it seems that your switching process operates at a considerably slower rate.

• 20-02-2025
• Jonnie_R

Jonnie_R commented: The frequency of testing the transistor output in relation to its actual usage is not a significant factor, as the wear on the transistor for your particular application will be minimal and likely challenging to quantify. The primary culprit behind your failure is likely some form of voltage disturbance, which isn't attributed to wear. If your switching cycles operated in the megahertz (MHz) range, then wear might be a consideration; however, it seems that your switching process is relatively slow. It's important to note that MTTFd (Mean Time To Failure for dangerous failures) is based on statistical data.

• 21-02-2025
• ivo.maenen

Jonnie_R noted that the frequency of testing the transistor output in relation to its usage is not particularly significant. In most applications, the wear on a transistor will be minimal and challenging to quantify. The primary reason for any failure you're experiencing is most likely a voltage disturbance, which is not related to wear and tear. If your switching cycles were operating in the megahertz range, you could consider wear as a factor, but it's likely that your switching process is much slower. For any application, particularly those involving safety-critical operations, it is imperative to adhere to the manufacturer's guidelines regarding usage limitations. This includes considerations such as switching frequency, voltage supply range, load conditions, and safety protections. Failure to follow these specifications will render metrics like B10 or Mean Time to Failure Demand (MTTFD) ineffective.

• 22-02-2025
• ndzied1

This information is derived from the same datasheet. Did the calculation of a Mean Time To Failure (MTTF) of 2,142 years come from testing 2,142 units, operating them at a frequency of 2,000 Hz, which resulted in one failure after a year? This method seems rather simplistic for such a significant figure.

• 22-02-2025
• UKB

UKB stated: “This information comes from the same datasheet. Did they truly determine the Mean Time To Failure (MTTF) of 2142 years by taking 2142 units, operating them at 2000Hz, and concluding that since one failed after a year, the MTTF is 2142 years? That seems a bit simplistic.” To clarify, the answer is no. The MTTFd (Mean Time To Dangerous Failure) for solid-state safety devices involves complex engineering calculations that consider the specifications of each component within the device. This approach is akin to how engineers evaluate the MTTFd for all safety products within a given safety system. It's essential to note that MTTFd for solid-state devices is NOT determined through standard product testing. In contrast, electro-mechanical safety devices—like tongue interlocks and conventional contactors—are specified based on extensive mechanical testing. (Editing Note: While product testing is indeed conducted by vendors on safety products and their components, it is critical to highlight that this testing is not the primary method used to specify MTTFd for solid-state safety devices.) Any third-party certification agency, typically affiliated with TUV organizations, would have validated the MTTFd calculations during the certification process, ensuring compliance and reliability of the solid-state safety product.

• 23-02-2025
• brianschriver

User ndzied1 commented: When utilizing any application, particularly in critical safety operations, it's essential to adhere strictly to the manufacturer’s specified usage limits. This includes factors like switching frequency, voltage supply range, load capacity, and protection mechanisms. Failing to comply with these guidelines renders metrics like B10 or MTTFD irrelevant. To clarify, I did not suggest that you shouldn’t follow these protocols; I merely highlighted that unlike relay contacts, transistors experience minimal wear.

• 24-02-2025
• Jonnie_R