MTBF (mean time between failure) is the English full name of "mean time between failure". Is to measure the reliability of a product (especially electrical products). The unit is "hour". It reflects the time quality of the product, and is a kind of ability to keep the function of the product within the specified time. Specifically, it refers to the average working time between two adjacent failures, also known as the average failure interval. Generally speaking, the product with less faults has high reliability. The ratio of the total number of faults to the total number of life units is called "failure rate". It is only applicable to Repairable Products. At the same time, the ratio of the total working time and the number of failures of the product in the total use stage is also specified as MTBF. Generally, the MTBF of disk array products should not be less than 50000 hours.
MTBF is the abbreviation of mean time between failure, which means the mean time between failures, an important measure of reliability.
Their transformation formula is: r = e ^ (- λ t)，MTBF=1/ λ，λ It's the probability of failure.
The calculation method of MTBF is as follows
1. According to the definition of MTBF, the ratio of cumulative working time and failure times of the product in the total use stage is defined as MTBF. Exponential distribution is the most commonly used probability distribution in reliability statistical analysis. The MTBF value of exponential distribution is failure rate λ So once you know λ The reliability function can be used to estimate the reliability of products
MTBF = total operating time (HRS) / total failures
The estimated value of MTBF accords with the principle of chi square distribution
CHIINV(probability,degrees_ freedom)X2(probability,degrees_ freedom)
Therefore, the formula is as follows:
T = total hours
R = number of failures
Φ= Confidence interval
Note: if there are no failures, then: mtbflower = t / - ln (confidence interval)
Reliability is designed, so the MTBF of the equipment is also designed.
The product achieves the qualitative and quantitative requirements of reliability through reliability design in the development stage. The general use index of quantitative requirements is MTBF, which is divided into two requirements: the specified value and the minimum acceptable value. MTBF can be adjusted in the development stage, and after the design is finalized, MTBF is also finalized with the product.
The main consideration in MTBF calculation is the failure rate of each device in the product. However, the failure rate of devices will be greatly different in different environments and different use conditions. For example, the reliability values of the same product in different environments, such as laboratory and offshore platform, are definitely different; Another example is that the failure rate of a capacitor with rated voltage of 16V is definitely different when the actual voltage is 25V and 5V. Therefore, the above factors must be considered when calculating the reliability index. All the above factors can hardly be calculated manually, but with the help of software such as mtbfcal and its huge parameter library, we can easily get the MTBF value.
Objective: to analyze MTBF
1. The key countermeasures for high frequency fault parts and the technical transformation basis for prolonging the service life of parts.
2. Calculate the life cycle of parts and make the best maintenance plan.
3. The selection of spot inspection objects and items and the setting and improvement of spot inspection benchmark.
4. Used to guide internal and external maintenance work assignment. According to the evaluation of the company's equipment repair ability, the internal risk of maintenance quality and equipment efficiency is determined by the different types of equipment and operation, which is an important reference for maintenance outsourcing.
5. Set spare parts benchmark. The reserve items and basic inventory quantity of mechanical and electrical parts should be judged according to the MTBF record analysis, so as to make the inventory level reach the most economical state.
6. It can be used as a reference for selecting the key improvement points of maintenance technology. In order to improve the start-up rate of equipment, it is necessary to shorten the time of long-time maintenance, engineering adjustment and switching related to equipment shutdown. Therefore, it is necessary to inspect the maintenance operation method, and the selection of inspection items and priorities should be based on the analysis record of MTBF.
7. It is used to set the estimated running time standard for the equipment object, and to select the maintenance operation and study the maintenance time standard. The setting of estimated time standard for maintenance plan and the selection of maintenance operation must consider the factors such as the difference between the equipment maintenance cycle or standard time value and the actual maintenance time, and the characteristics of corresponding maintenance operation. Therefore, the MTBF analysis table is very necessary.
8. Reference for drawing arrangement and re selection of key equipment or parts. The information recorded in MTBF analysis record sheet, such as equipment parts modification project or friction deterioration, as well as equipment drawing modification or pre production, can make engineering drawing management easier through frequent analysis and inspection and importance ranking management.
9. Set and revise the operation standard and decide the responsibility assignment of equipment maintenance business.
10. Provide technical data of equipment reliability and maintainability design. The most important part of maintenance technology is to collect the technical information about the reliability and maintainability design of the equipment based on the MTBF analysis table, so as to provide the reference for the design department when designing the equipment.
