Product Lifecycle

The B10 value is used in particular in reliability and quality testing. It indicates the operating time after which 10% of a group of products or devices will fail or no longer meet the required specifications. Due to a wide variety of influences, the test cannot be generalized (typical applications).

The B10 value is part of the "Weibull analysis" used in reliability engineering. In many industries where reliability is critical, the B10 value is considered an important metric. The B10 value is used in the development phase, quality control, determining guarantees and ensures, maintenance planning, risk management, customer information and marketing.

The B10d value is used in the assessment of safety functions and, according to ISO 13849-1, indicates how many switching cycles have elapsed before dangerous failures occur in 10% of the units under consideration. The B10d value is therefore relevant for the preparation of a risk and hazard analysis. If the number of dangerous failures is not known, the following calculation is recommended: B10d = 2*B10. However, it is not possible to calculate the B10d value for an individual component of a workpiece. The B10d value is used for the evaluation of safety functions, norms and standards, safety-relevant components, certification of safety-critical systems, risk assessment, planning of safety-related measures, maintenance planning and life cost analysis.

MTTF stands for Mean Time To Failure and indicates the average service life of a component. According to EN ISO 13849-1, the performance level can be calculated on the basis of the MTTF. The MTTF is used for risk assessments of components and systems where failure is not an immediate risk. The MTTF value is also important for CE marking. The MTTF is given in hours and indicates how long, on average, a particular component or system is expected to function fault-free. The MTTF is determined by empirical values or specific tests. For example, several devices are observed over a lengthy period of time until they all fail:

MTTF is the sum of the operating times of all devices until complete failure divided by the number of devices examined. MTTF is used in the development phase, quality assurance, when determining guarantees and ensures, in brand communication, in maintenance planning and in lifecycle cost analysis.

In the context of functional safety, terms such as MTTF_d (Mean Time To Dangerous Failure) are used to describe the time to failure of safety-critical parts where a failure can lead to dangerous situations. The MTTF_d value can be divided into 3 areas.

The MTTF_d value can be calculated using this general formula

MTTF_d = B10d / (0.1*n)

The MTTF_d value is used in a functional safety analysis, for the evaluation of safety-relevant components, for norms and standards, for the evaluation of safety functions, for the calculation of the probability of failure, for the certification of safety-critical systems, for risk assessment and for the planning of safety-related measures.

The term "PFH" stands for "Probability of Dangerous Failure per Hour". The PFH value is a reliability indicator used in the context of functional safety, particularly in standards such as ISO 13849-1 and IEC 62061.

The PFH value quantifies the probability that a safety-relevant function in a system will exhibit a dangerous fault within one hour. The PFH is calculated as follows for a subsystem:

PFH = λ * 1h

For an entire system, the PFH is calculated differently:

PFH_total= ∑^N_i=1 PFH_i = PFH₁ + PFH₂ + ... + PFH_N

In functional safety, it is important to keep the PFH value as low as possible to ensure that the probability of dangerous errors is at an acceptable level. The PFH value is an important size in the context of risk assessment and safety evaluation.

It should be noted that the PFH in the context of functional safety is specifically aimed at safety-critical systems and is not applicable to general products or applications.

The PFH value is used in the evaluation of safety-critical systems, in the evaluation of safety functions, for norms and standards, in risk assessments, for the certification of products and systems and in the development of safety-critical software.

The term PFD stands for "Probability of Failure on Demand" and is used in the context of functional safety.

The PFD value indicates the probability of a safety-critical function or system failing when it is activated or requested.

It is an important key figure when assessing the reliability of safety-relevant systems and functions. The PFD value is often used in connection with the Safety Integrity Level (SIL) to quantify the power of safety functions. The PFD value is generally calculated using the following formula:

PFD = 1 / MTBF

It is important to keep the PFD value as low as possible to ensure the safety of the system. A low PFD value means higher reliability and a lower probability of faults when required. The PFD value is used in the evaluation of safety-critical systems, for safety analyses, in the development phase, for norms and standards, for the certification of products and systems and for the evaluation of safety instrumentation.

MTTR stands for "Mean Time To Repair". The MTTR value is a reliability indicator that shows the average time required to restore or repair a system or components after a failure.

The MTTR value is required to assess the availability and reliability of systems. A low MTTR value indicates that a system can be restored to normal operation quickly, while a high MTTR value indicates that the repair will take longer. The calculation refers to the average duration of repair work after a failure and takes into account relevant factors such as the time needed to diagnose the problem, order spare parts or other preparatory measures. The formula for calculating the MTTR is therefore

MTTR = total downtime / total number of breakdowns

For example: If a system fails three times in a month and has resulted in a total downtime of 6 hours, then the MTTR is 2 hours.

The MTTR value is particularly important in industries where the continuous availability of systems is essential. The MTTR value is often used in connection with other reliability indicators such as MTBF. The MTTR is used in maintenance planning, for forecasting repair times, in maintenance management, for service level agreements (SLAs), for a lifecycle cost analysis, for continuous improvement, for risk assessment or emergency planning.

The term MTBF stands for "Mean Time Between Failures". This indicates the average amount of operating time that elapses between two consecutive failures of a system. The MTBF is usually used to evaluate the reliability of products, devices or systems. It is the inverse rate of the probability of failure and is expressed in time units such as hours or years. A high MTBF value indicates high reliability, as there are longer periods between failures. The MTBF value is calculated by dividing the total operating time by the number of failures:

MTBF = total operating time / number of failures

Or

MTBF = MTTR + MTTF

The MTBF value is particularly relevant in industries where reliability is of critical importance. As already mentioned with the MTTR value, the MTTR value and the MTBF value are often used together. The MTBF value has applications in product development, quality assurance, maintenance planning, risk assessment, lifecycle cost analysis, warranties and ensures, and as an aid to decision-making for customers and continuous improvement.

The term SIL stands for "Safety Integrity Level" and refers to a risk assessment in the area of functional safety. SIL is a dimension for the reliability of a safety function in a system. The scale ranges from SIL 1 (lowest reliability) to SIL 4 (highest reliability). The SIL safety requirement level serves as an assessment method for the reliability of a system, whereby this assessment is always carried out in the context of the existing hazards. The classification depends on various factors, including the probability and potential consequences of hazards. Specific methods and standards, such as the IEC 61508 series of standards, are usually used for the assessment.

1. B10 value: Test after which operating time 10% of a group of products fail/no longer meet the required specifications

2. B10d = 2 * B10

3. MTTF = Sum of the operating times of all devices until complete failure / Number of devices tested

4. MTTF_d value: MTTF_d = B10d / (0.1*n)

5. PFH:

For a subsystem: PFH = λ * 1h

For an entire system: PFH_total = ∑^N_i=1 PFH_i = PFH₁ + PFH₂ + ... + PFH_N

6. PFD = 0.5*T / (MTBF + 0.5*T)

7. MTTR = Total downtime / Total number of failures

8. MTBF = Total operating time / Total number of failures

9. SIL: Classification depends on many different factors/tests

Explanation:

n : Number of devices tested

λ : Failure rate

T : Maintenance interval/time unit

*For 10d value only calculation if no knowledge of failure rate available