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