Laboratory comparison test of the hottest light ve

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Light vehicle emission laboratory comparison test

Abstract: inter laboratory comparison is "the organization, implementation and evaluation of tests on the same or similar test items by two or more laboratories according to predetermined conditions". The comparison between motor vehicle emission laboratories is to evaluate the testing ability of motor vehicle emission laboratories, improve the laboratory quality assurance system, and ensure the consistency and effectiveness of testing results between different laboratories. This paper introduces the inter laboratory comparison test of light vehicle emissions organized and implemented in 2002, analyzes the factors affecting the test results, and discusses the data processing method using the z-ratio score as the laboratory capacity statistics

key words: laboratory comparison motor vehicle emission laboratory Z ratio score

since the late 1980s, China has successively introduced internationally advanced test equipment, established a number of motor vehicle emission laboratories that meet international and national emission standards, and carried out research on the detection and control technology of motor vehicle emissions. The test data provided by it is an important basis for China to evaluate the control level of vehicle emissions and formulate policies to control vehicle emissions. It is of great significance to improve the testing quality of vehicle emission laboratory and ensure the correctness and effectiveness of test data. Inter laboratory comparison is an important way to ensure the consistency and effectiveness of test results between different laboratories, and provides an objective means for laboratories to evaluate and prove the reliability of their data. Iso/iec 17025 "General requirements for the ability of testing and calibration laboratories" clearly states that laboratories should "participate in the comparison test or ability verification plan between laboratories", "regularly use certified reference materials for internal quality control", "to monitor the effectiveness of testing and calibration". China has signed a mutual appointment agreement with the International Laboratory Accreditation Cooperation (ILAC) to mutually recognize the certificates/reports issued by accredited laboratories, so as to achieve international standards. Therefore, the role of inter laboratory comparison test will become more and more important

the light vehicle emission laboratory comparison test carried out in 2002 is the requirement of the "China EU cooperation project sub project 3 - quality control of China's vehicle emission laboratory" project, which is in the charge of the State Environmental Protection Administration. It was carried out in eight light vehicle emission laboratories in Beijing, Tianjin and Shanghai. Various factors affecting the emission laboratory test results and evaluation methods were studied and analyzed, It provides a useful attempt to evaluate and verify the laboratory testing ability and quality assurance system

1 comparison test status between domestic and foreign motor vehicle emission laboratories

in 1994, 1996 and 1999, China's automotive industry held three comparison tests of light vehicle emission laboratories, which played a positive role in improving laboratory testing level, deepening understanding of emission standards and improving personnel quality. Due to the particularity and complexity of emission test, how to evaluate and verify the ability of the laboratory through comparative test still needs further research

Europe has strict systems in laboratory management. In order to reduce the difference of test results between laboratories, the main measure taken by emission laboratories together with European certification bodies and manufacturers is to conduct regular comparisons between laboratories. This work has been carried out for 20 years. Whether it is often in trouble has become a necessary work for emission laboratories every year, which is called "round robin testing programs". There are many forms of organization: comparison between laboratories of certification bodies, between certification bodies and manufacturers' laboratories, and between laboratories within manufacturers (such as Volkswagen, etc.). Through the comparison test activities, all laboratories have a common understanding of the standards, standardized the operating procedures, improved the technical quality of test personnel, and ensured the consistency of test results between laboratories

the National Environmental Protection Agency (EPA) has two expert working groups, which are responsible for studying and coordinating technical issues related to vehicle emissions, including the construction of quality systems in various laboratories. The comparison test between laboratories is carried out between laboratories in a cyclic and continuous manner for one year. The emission Laboratory of EPA is called "golden standard" as a standard laboratory

2 importance of vehicle emission laboratory comparison test

vehicle emission test mainly includes light vehicle emission test (gasoline vehicle, diesel vehicle), fuel evaporation test, crankcase emission test, durability test of pollution control device, gasoline engine emission test, diesel engine emission test, diesel vehicle free acceleration smoke test, motorcycle working condition method emission test, etc. Taking the light vehicle emission laboratory as an example, the typical light vehicle emission laboratory is shown in the following figure 1:

1-chassis dynamometer 2-Fan 3-test vehicle 4-driver's driving column 5-mixing room 6-laboratory environmental space 7-emission analyzer

8-sampling bag 9-dilution air filter 10-laminar flow meter 11-blower 12-standard gas

Figure 1 the typical light vehicle emission laboratory

can be seen from the figure, The emission detection of motor vehicles requires many instruments and equipment, high technical content, and complex test methods, involving the working mechanism and combustion process of motor vehicles and engines; Use and calibration of high-precision electromechanical integration instruments and equipment; High purity standard materials; Facilities and environment; Ability and experience of test personnel, etc. During the test, the driver's operation, the temperature and humidity of the environment and their changes, the systematic errors of instruments and equipment, the errors of standard gases, some differences before and during the test, etc. will affect the emission test results, and it is difficult to directly determine the causes of possible data deviation. The degree of influence of these factors (such as statistical laws) has not been quantitatively analyzed. (in the United States in the 1970s, and later, Volkswagen has done relevant research.) these influencing factors will be directly reflected in the laboratory test results. In addition, another important factor is the test object itself - the emission content of the test vehicle itself is uncertain in each test. Therefore, whether the test data issued by the laboratory is correct and reliable, in addition to the fact that the laboratory has perfect quality assurance, which will provide a strong quantitative support system for the fair selection and use of packaging materials after the formal implementation, and regularly carry out internal quality monitoring and control with standard sample vehicles to ensure the stability of the test system, the most important thing is to evaluate and prove the reliability of the issued data through comparative tests between laboratories

3 implementation process of comparison test

this inter laboratory comparison test of light vehicle emissions is mainly carried out according to international and national standards such as iso/iec guidelines (1997) "establishment and implementation of capability verification test scheme", iso/iec 17025 "General requirements for the qualification of testing and calibration laboratories". Before the comparison test, expert seminars were held and implementation rules were formulated. The whole process was carried out in strict accordance with the procedure, and experts and testers were organized to observe and communicate. The participating laboratories include 6 in Beijing, 1 in Tianjin and 1 in Shanghai, with a total of 8 light vehicle emission laboratories. Among them, five light vehicle emission laboratories are authorized by the state to undertake the task of light vehicle emission testing. Three laboratories have been accredited by China National Accreditation Commission for laboratories

3.1 the basic parameters of the test sample car are as follows:

during the whole activity, the sample car is in a stable state without fault code display. After returning to the original laboratory, there was no obvious abnormality in the emission test results. The comparison test completed by each laboratory is generally carried out for days, including the chassis dynamometer sliding setting and pre-test for 1 day and the emission detection test for 3 consecutive days. The sample vehicle is transported by Trailer between cities

3.2 main items in the comparison test:

· verification of standard reference gas

· chassis dynamometer coast down test

· three times gb18352 Exhaust pollutant test after cold start (type I test) specified in the test method for light vehicle emission pollutants

4 test results and analysis

4.1 verification of standard reference gases

in order to verify the overall accuracy of emission laboratory analyzers and standard gases, the verification project of "standard reference gases" was specially carried out in this comparison activity. The laboratory first completes the calibration and inspection of the zero point and span point of the emission analyzer with its own standard gas, and then connects the "standard reference gas" with unknown concentration in the laboratory (CO 257ppm, no 81.3ppm, propane 89.8ppm, CO2 1.8%) to the analyzer path. After the flow and gas concentration are stable, record the displayed value of the analyzer and calculate the relative error with the nominal concentration of the standard reference gas. According to the provisions of the national standard, the analyzer is allowed to have a reading error of ± 2% of the standard gas, and the nominal concentration of the "standard reference gas" used also has an uncertainty of ± 1%. Considering the possibility of the maximum error, the reading of the analyzer within the range of ± 3% will be considered normal. Figure 2 shows the verification results of standard reference gas. It can be seen that the relative error of analyzer readings in most laboratories 5 Conclusion

under the full support of motor vehicle emission laboratories, how to choose the electronic tensile machine with high practicability, this comparison test was a complete success. Through the comparative analysis of the test results, this paper studies many factors that affect the vehicle emission test data, and how to organize and implement the comparative test. In order to achieve the goal of synchronizing the emission control of motor vehicles with the international level set by the Chinese government in 2010, it is of great significance to carry out the comparison test between motor vehicle emission laboratories in an organized and planned way among a number of high-level emission laboratories that have been and are being established to meet the requirements of corresponding regulations and standards to improve the laboratory quality assurance system and ensure the consistency and effectiveness of the test results between different laboratories at home and abroad


1 ISO 1993 statistics vocabulary and symbols (1993)

2 iso/iec guidelines ability verification tests using inter laboratory comparisons part I: establishment and implementation of ability verification test scheme (1997)

3 guide to Nata proficiency testing (1997)

4 iso/iec 17025 General requirements for the competence of testing and calibration laboratories (1999) (end)

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