What is Variable Life?

The working time corresponding to a given reliability is called Q-precentile life.

The working time corresponding to a given reliability is called Q-precentile life.

Chinese name

Reliable life

Foreign name

Q-precentile life

given

Reliability

Find out

Corresponding working hours

Introduction to Reliable Life

If the given reliability is R = 0.99, its corresponding working time is recorded as t (0.99), which is the reliable life. When the reliability is unknown, but as long as its working time tt (0.99), the reliability of the product will be lower than the given value of 99%, and more products may fail.

Let the reliability of the product be R (t) and make the reliability equal to the time t when the specified value r is the reliable life.

Reliable life and reliability

The so-called product reliability, in fact, describes the quality of the product in terms of time. Its classic definition is: the general satisfaction of completing the prescribed function satisfactorily under the prescribed conditions and within the prescribed time. For example, a refrigerator. Manufacturers design it to have a service life of 10 years, so can the produced refrigerator work satisfactorily for 10 years in the actual work in the future? In other words, how likely is it to work for 10 years? The greater the probability, the more reliable Sex is super high, otherwise it is low. The classic definition emphasizes a total of four aspects, namely probability, performance requirements, use conditions, and trouble-free working time ^[1] .

It can be determined that the function of fault and service life changes with time and presents different characteristics ^[1] .

Life curve

As can be seen from the figure, the failure period of any electrical equipment can be divided into three phases, namely early failure, use-time failure, and wear-out failure. Early failure generally refers to the time range of about half a year during storage or sales in the warehouse, during transportation, and after the user purchases. Such failures are generally of primary origin, some are problems in design and production, some are process problems, and some are unqualified components that have not been removed and fail. If it is a transportation failure, such as damage, component crushing, etc., the AVX tantalum capacitor failure will be revealed when it is purchased in the store, and generally will not reach the user. These products are directly responsible by the manufacturer or wholesaler. However, the early failures in the monthly household use process generally manifest as: poor welding or sealing, and poor contacts. Improper assembly of components, occasional failures, etc., it does not matter, because general large electronic products, this time are guaranteed by the manufacturer or special maintenance outlets. After the early failure period, the product is aged and begins to enter the use period. During this period, the failure rate is the smallest, and the curve is relatively flat. The service life we usually call is mostly this period of time ^. .

Of course, different electronic products have different service lives. Most of the failures that occur during the service period are pathogenic, and are generally due to the performance change or occasional destructive damage of a certain component or a few poorly performing components. Such as human failure, lightning damage, etc., generally replace a single component, readjust the circuit characteristics, the fault can be eliminated. After the use period, the whole machine starts to enter the loss period. During this period, the circuit has more and more tantalum capacitor barriers, and it will be more and more, and sometimes there will be several simultaneous failures. Failures during this period are damaging. Because electrical equipment is generally more complicated, more components are used, and after a long period of wear and tear, the component's persistence becomes worse and its performance deteriorates. Failure due to fatigue. In addition to replacing the failed components during the wear period, the entire machine must be debugged. Sometimes, there are many components that need to be replaced, and it is not even cost effective to repair them ^[1] .

MTBF Reliable life MTBF calculation of life reliability test

It is used to clarify that the standard test conditions and test methods are used when components and products are tested for reliability and life. It is applicable to the reliability test and risk assessment of all components during sample recognition, product development design maturity / product maturity (DMT / PMT) verification, and routine ORT routine tests ^[2] .

MTBF: Mean Time Between Failures, English full name: MeanTimeBetweenFailure. Definition: Measure the reliability index of a product (especially electrical products), the unit is "hour". It reflects the time quality of the product, it is a kind of ability to reflect the product's ability to maintain function within a specified time. The average working time between two adjacent failures, also known as the average failure interval, is only applicable to repairable products. It also specifies that the ratio of the cumulative working time of the product to the number of failures during the total use phase is MTBF ^[2] .

Accelerated Life Testing (Accelerated Life Testing ) : 1 The purpose of performing a life test is to evaluate the service life of the product in a given environment; 2 The conventional test takes a long time and requires a large amount of money, and product reliability information cannot be obtained in time Improve; 3 can use the accelerated life test method in the laboratory to evaluate the service life of the product within an acceptable test time; 4 is based on the physical and time, accelerate the cause of product degradation, test in a shorter time To estimate the life or failure rate of the product in normal use. But the basic condition is that the original design characteristics cannot be destroyed; 5 In general, the three factors considered in the accelerated life test are environmental stress, the number of test samples and the test time; 6 General Almost all the reliability modes and acceleration modes of electronic and industrial control parts can be checked from the US military specifications or related standards, or they can be tested and analyzed by themselves to obtain their mathematical experience formula; 7 If temperature is the only acceleration factor of the product, Azerbaijan can be used Model, the most commonly used model; 8 Introduces stresses other than temperature, such as humidity, voltage, mechanical stress, etc., is the Ailing model (E yringModel), products suitable for this mode include electric lamps, liquid crystal display elements, capacitors, etc .; 9 Inverse Power Law is applicable to metal and non-metal materials, such as bearings and electronic equipment; 10 Composite Model (CombinationModel) is applicable to At the same time, temperature and voltage are considered as electronic materials for environmental stress (for example, the capacitor is the formula for calculating the life of electrolytic capacitors); 11 In general, active electronic parts are fully applicable to the Aster model, and electronic and industrial control products can also be applied to Aster The reason is that the failure mode of the finished lamp is composed of most active electronic parts. Therefore, the Ashfield model is widely used in the electronics and industrial control products industry ^[2] .