The MTTF (Mean Time To Failure) of our products, according to EN ISO 13849-1, depends on their usage, specifically the number of cycles per year.

• MTBF (Mean Time Between Failures) = MTTF (Mean Time To Failure) + MTTR (Mean Time To Repair)

In our case, the MTTR is negligible because the component is typically replaced if it fails. The MTTF calculation can be related to the MTTFd (Mean Time To Dangerous Failure), which indicates the average time before a dangerous failure occurs. For pressure switches, according to EN ISO 13849-1, the formula is:

MTTFd = B10d / (0.1 * nop)

Where:

• nop = number of cycles per year
• B10d = number of cycles until 10% of the components experience a dangerous failure

Example for Pressure Switches:

• If the current is <20mA, B10d = 1.000.000 cycles.
• If the current is >20mA, B10d = 100.000 cycles.

For a current >20mA: MTTFd = 100,000 / (0.1 * nop) = 10^6 / nop

The customer can calculate the MTTF by inserting the expected number of cycles per year for their application.

For example, if the pressure switch operates once per minute: nop = 1 * 60 * 8 * 220 = 105.600 cycles/year MTTFd = 106 / 105.600 = 9,47 years

Example for Level Switches:

For LM1…XIA, considering the low voltages and currents, we estimate 10^5 cycles for safety. MTTFd = 100.000 / (0.1 * nop) = 106 / nop

For example, if the level switch operates once every 10 minutes: nop = 1 * 8 * 6 * 220 = 10.560 cycles/year MTTFd = 106 / 1760 = 94 years