GB/T 24986.1-2020Testing evaluation methods for reliability on household and similar electrical appliances —Part 1: General requirements (English PDF)

3.1 Reliability

3.14 Mean operating time to first failure; MTTFF

the expected value of working time before the first failure [GB/T 2900.99-2016, definition 192-05-12]

3.15 Reliability growth testing

an iterative process to improve reliability through testing until failure, failure analysis, corrective action implementation, and further testing

NOTE: Corrective actions can be applied to existing or new test products. [GB/T 2900.99-2016, definition 192-12-06]

4.1 Selection of reliability evaluation parameters

The selection of reliability evaluation parameters includes the following aspects:

a) The basic reliability reflects the equipment's demand for maintenance manpower costs and logistical support resources. When determining the basic reliability indicators, all life units and all failures of the equipment shall be counted. The common basic reliability parameter is the mean time between failure;

b) When determining the task reliability parameters, only the failures that affect the completion of the task during the task are considered. Common task reliability parameters include task reliability;

c) To monitor and verify the earlier failure of the appliance, the mean operating time to first failure (MTTFF) can be used as the evaluation parameter;

d) For the appliance that require control of the number of failures, select failure rate, mean time between failure or reliability parameters;

e) For the appliance with wear faults, their life characteristics can be described in terms of reliable life and useful life.

4.2 Determination of reliability evaluation indicators

The reliability evaluation indicator is the required value of the reliability parameter. Based on user surveys and data accumulation, weigh it according to the following factors:

a) The user needs;

b) The level of existing equipment;

c) The feasibility in technical and economic implementation.

6.1 Overview

The reliability evaluation method is a method or way of reliability evaluation. It is mainly a combination of qualitative analysis and quantitative evaluation.

Reliability evaluation usually can use methods such as FMEA, FTA, comparative analysis of the reliability level of similar electrical appliances, and reliability test data analysis to evaluate the reliability level of the appliance.

6.2 Qualitative analysis

The purpose of qualitative analysis and the corresponding methods that can be used are as follows:

a) Explain the inheritance of the appliance and whether it is possible to adopt mature technology in the design and craftsmanship of the appliance. […]

6.3.2 Expert scoring method

The expert scoring method relies on experienced technicians to score according to several factors. The factors considered in the scoring can be determined according to the characteristics of the electrical appliance. The four commonly used scoring factors are: complexity, technical development level, working hours, and environmental conditions. According to the scoring result, the failure rate of the remaining units is calculated from the known failure rate of a certain unit according to the scoring coefficient.

6.3.3 Similar product method

The similar product method is a predictive method that uses specific experience gained from similar appliances. The fastest way to estimate the reliability evaluation is to compare the appliance being designed and developed with a similar appliance. The reliability of the latter has been determined by a certain method and has been evaluated. The comparison between similar appliances mainly includes the following aspects:

a) Comparison of the structure and performance of the appliance;

b) Design similarity;

c) Similarity of manufacturing.

6.3.4 Component counting method

The component counting method is the prediction method used in the preliminary design stage. At this stage, the number of each general component has been basically determined. In the later stages of design, development, and manufacturing, the complexity of the entire design is not expected to change significantly. The component counting method recognizes that the life of components is exponentially distributed. The information expected by the component counting method is:

a) Common types of components;

b) Number of components;

c) Component quality level;

d) Working environment of the appliance.

6.3.5 Map evaluation method

The map evaluation method uses a special probability plot paper, and the cumulative distribution function studied on the probability paper can be drawn into a straight line, and the parameters of the distribution are finally determined.

The average rank and median rank of cumulative percentages are used in probability plotting. The average rank is suitable for symmetrical distributions, such as normal distributions. The median rank applies to asymmetric distributions, such as Weibull distribution.

7.1 Test arrangement

When arranging reliability tests for the appliance products, consider:

a) All tests that can provide information for evaluating and improving the reliability of appliances, use the available information of these tests as much as possible or carry out in combination with these tests, such as performance tests, so as to make full use of resources, reduce repetitive costs, improve test efficiency, and ensure that defects that are often ignored in individual tests will not be missed;

b) The reliability test of the appliance can be combined with the durability test of the appliance. The type and magnitude of environmental stress and working stress shall simulate the environmental and working conditions expected to be used;

c) The use of accelerated reliability test can significantly shorten the test time, according to the application guidance of the accelerated test method for appliance reliability specified in GB/T 34434.

7.2 Test conditions

When determining the reliability test conditions, it shall pay attention to:

a) When determining the reliability test conditions during the design and development process, consideration shall be given to exposing the defects in the design, materials, and craftsmanship that exist in the appliance;

b) When carrying out reliability appraisal, acceptance test and reliability growth test, the authenticity of the test must first be considered. Simulate the actual use environment of electrical appliances, so that the appliance can withstand the type, level and duration of stress experienced in use.

The selected stress can fully expose the failures that occur in actual use, and will not induce failures that will not occur in actual use.

C.1 Verification method of useful life indicators

The verification method of useful life is generally divided into engineering empirical method and analytical method. The verification of the appliance's useful life indicators adopts the engineering empirical method.

C.2 Test conditions

The test conditions of the appliance durability test are carried out according to the test requirements of the specific product.

C.3 Test time

The single test time of the appliance durability test is 1.2 to 1.5 times the rated useful life or the value to be verified.

The least total test time TL>=n×K×T0. Where, n is the number of tested products, T0 is the specified life of the tested products, and K is the engineering experience coefficient. The specific value can be negotiated by the manufacturer and the ordering party based on factors such as the importance of the product and the experience of similar products.

C.4 Number of tested samples

The number of samples for the durability test of the appliance is generally not less than 2 sets.

Products of the same series with similar designs and the same failure mode can be combined and verified with different models of this series of products.

C.5 Selection of tested samples

According to the actual situation, the sample selection method can be any one of the following methods.

C.5.1 When the product to be verified requires reliability index evaluation at the same time, before the start of the appliance MTBF evaluation test, n of them shall be randomly designated as durability test samples.

C.5.2 In other cases, randomly select products from finalized state products or […]