GB/T 2421-1999 Environmental testing for electric and electronic products Part 1: General
Some standard content:
GB/T2421-1999
This standard is equivalent to the International Electrotechnical Commission standard IEC68-1:1988 (6th edition) "Environmental testing Part 1: General". And according to its amendment No. 1 (May 1992), 5.3 "Atmospheric conditions for measurement and testing" was modified. GB/T2421-1989 was drafted by equivalently adopting IEC68-1:1982 (5th edition) "Basic environmental testing procedures Part 1: General".
This standard replaces GB/T2421--1989 "General principles for basic environmental testing procedures for electrical and electronic products". According to the relevant provisions of GB/T1.1-1993 on equivalent adoption and equivalent adoption of international standards, this standard is the same as IEC68-1:1988 (6th edition) in terms of technical content and writing format. The relevant standard modification information after 1988 has also been modified accordingly in this standard. In accordance with my country's policy of adopting international standards, the referenced standards in the IEC preamble have been added with the status of the international standards adopted by the national standards. This is conducive to the parties using this standard to understand the status of the international standards adopted by this standard, and also provides the parties using this standard with information on the differences between the national standards and the IEC standards.
Appendix A and Appendix B of this standard are both appendices to the standard. This standard was proposed by the State Bureau of Machinery Industry. This standard is under the jurisdiction of the National Technical Committee for Standardization of Environmental Conditions and Environmental Testing for Electrical and Electronic Products. The drafting unit of this standard: Guangzhou Electric Science Research Institute. The main drafters of this standard: Zhang Qiangying and Zhang Chi This standard was first issued in 1981 and revised for the first time in 1989. GB/T 24211999
IEC Foreword
1) IEC's formal resolutions or agreements on technical issues are formulated by technical committees represented by national committees with special interests in the issue, and express the international consensus on the issue as accurately as possible. 2) These resolutions and agreements are recommended for international use and are accepted by national committees in this sense. 3) In order to promote international unification, IEC hopes that all national committees, under the conditions permitted by their national conditions, will adopt the contents of IEC standards as their national standards as much as possible. Any inconsistencies between IEC standards and corresponding national standards should be clearly pointed out in the national standards as much as possible.
GB/T 2421--1999
IEC Preface
This standard was developed by IECTC50 (Environmental Testing) Technical Committee. This standard is the 6th edition and replaces IEC68-1:1982 (5th edition). The text of this standard is based on the following documents: June Method
50(CO)198
50(CO)205
Voting Report
50(CO)202
50(CO)208
Two-Month Procedure
50(CO)204
Full information on voting to approve this standard can be found in the voting report indicated in the table above. This standard references the following IEC standards:
Voting Report
50(CO)206
IEC50 (301, 302, 303): 1983 International Electrotechnical Vocabulary (IEV) Chapter 301: General Terms for Electrical Measurement; Chapter 302: Electrical Measuring Instruments; Chapter 303: Electronic Measuring Instruments (Trial Version)IEC68 Environmental Testing
IEC68-2 Part 2: Tests
IEC 68-2-14:1984 Test N: Temperature Change (GB/T2423.22--1987eqvIEC 68-2-14:1984) Test T: Soldering (GB/T2423.28---1982eqvIEC68-2-20:1979)IEC 68-2-20:1979
IEC 68-2-27:1987
IEC 68-2-38:1974
IEC 68-2-47:1982
Test Ea and guidance: shock (GB/T2423.5---1995idtIEC68-2-27:1987)Test Z/AD: temperature/humidity combined cycle test (GB/T2423.34--1986idtIEC68-238:1974)
Components, equipment and other products in dynamic tests such as shock (Ea), collision (Eb), vibration (Fc and Fd) and steady-state acceleration (Ga) Installation requirements and guidance (GB/T2423.43---1995idtIEC68-2-47:1982)
Guidelines for simulating storage effects using tests in IEC68 standards (GB/T2424.19--1984eqVIECIEC 68-2-48:1982
68-2-48: 1982 1st edition)
IEC68-3 Part 3: Background information
IEC68-3-1: 1974 Section 1: Low temperature and high temperature tests (GB/T 2424.1—1989eqvIEC 68-3-1: 1974 and JEC68-3-1A: 1978)
IEC68-3-1A: 1978 1st supplement
IEC68-4 Information for standard setters Test overview IEC160: 1963 Standard atmospheric conditions for testing IEC 271:1974
Basic terms, definitions and related mathematical methods for reliability (GB/T3187--1994 Reliability and maintainability terms)
Enclosure protection degree (GB4208--1984eqvIEC529:1976)IEC 529:1976
IEC695
Fire hazard test (GB/T5169-1985 series idteqv or neq: IEC695)IEC721 Classification and grading of environmental conditions
IEC721-1:1981 Part 1: Classification of environmental parameters and their severity classification (GB/T4796--1984idtIEC721-1:1981)
IEC721-2 Part 2: Environmental conditions occurring in nature (GB/T4797.1-1984neqIEC721-2-1:1982)GB/T24211999
IEC721-3 Part 3: Classification and grading of environmental parameter groups and their severity (GB/T4798.3-1990neqIEC7213-3:1994)
Guide 104:1984 Guidelines for the drafting of safety standards and the role of committees with safety guidance and safety organization functions Other referenced standards:
ISO 554:1976
Specification for standard atmospheric conditions for inspection or testing ISO 32051976
Preferred test temperature
National Standard of the People's Republic of China
Environmental testing for electric and electronic products
Part 1:General
Environmental testing for electric and electronic products-Part 1:General and guidance
1 Introduction
GB/T 2421 1999
idt IEC 68-1:1988
Replaces GB/T2421--1989
1.1 This standard is used when formulating relevant specifications for a certain type of product (electrical, electromechanical, electronic equipment and devices and their components, subassemblies, components, hereinafter collectively referred to as samples) so that the environmental testing of the product can be unified and reproducible. Note: Although this standard was originally formulated for electrical and electronic products, the environmental test methods are also applicable to other industrial products. "Environmental condition test" or "environmental test" refers to exposing samples to natural and artificial environments to evaluate their performance under the actual conditions of use, transportation and storage. This series of standards does not involve performance requirements for environmental test samples. During and after the environmental test, the allowable performance limits of the test samples are specified by the relevant specifications of the tested samples.
When drafting relevant standards and procurement contracts, these tests are specified only when the relevant samples require these tests, considering technical and economic reasons.
Environmental testing for electric and electronic products consists of the following parts: a) Part 1 (IEC68-1): details the general guidelines; Note: refer to IEC 68-2-48
b) Part 2 (IEC68-2): published in separate volumes, each volume introduces a group of tests or a specific test or their application guidelines; Note: refer to IEC 68-2-47.
c) Part 3 (IEC68~3): published in separate volumes, each volume introduces the background information of a group of tests; d) Part 4 (IEC68-4): provides information for the developers of the specification, published in two parts, of which Part 2 is in loose-leaf form and contains a summary of all current tests in IEC68-2. Note: Fire hazard tests are published separately as IEC695. 1.2 The following history summarizes the important features of this standard and its earlier versions. First edition (1954): It includes not only the "General Principles" section, but also many individual tests, which have now become part of the IEC68-2 series of publications.
Second edition (1960): The format was changed to "IEC68-1 General Principles", and the test was published separately as the IEC68-2 series of standards, and all test standards included severity levels.
Third edition (1968): The severity was reduced, and more definitions were modified and added in the first amendment in December 1972, and the climate type of the components was introduced. Recovery conditions--item (5.4) is used as normal application, so unless otherwise specified, all samples must be subjected to strictly controlled conditions. Supplement A was published in December 1974, adding definitions for comprehensive tests, combined tests and test sequences. Fourth edition (1978): This edition includes Amendment 1 and Supplement A of the third edition, and adds a modification of standard recovery conditions to the original 5.4 of the third edition, including recovery conditions with more tolerance for temperature and humidity. Approved by the State Administration of Quality and Technical Supervision on October 10, 1999 and implemented on May 1, 2000
GB/T 2421-—1999
Fifth edition (1982): This edition consists of the text of the fourth edition (including Chapter 10, Meaning of values) and an appendix giving general guidance on environmental testing.
Sixth edition (1988): This edition makes extensive editorial changes to the fifth edition, including technical content of IFC 160 that will be abolished and technical revisions to Chapter 7 and Appendix A.
1.3 The test methods forming part of this series of standards are designated by capital letters as follows*: A: Low temperature. ||tt ||B: High temperature.
C: Constant damp heat.
D: Alternating damp heat.
E: Impact (e.g. shock and collision).
F: Vibration.
G: Constant acceleration.
H: To be determined (originally assigned in the storage test see 1.1a) Note). J: Long.
K: Corrosive atmosphere (e.g. salt spray).
L: Sand and dust.
M: High or low pressure
N. Temperature change. ||tt ||P: To be determined (originally assigned to the "flammability" test, now discussed in the IEC695 fire hazard test method). Q: Sealing (including board sealing, container sealing and sealing to prevent fluid intrusion and leakage). R: Water (such as rain, dripping water).
S: Radiation (such as solar radiation, but not electromagnetic radiation). T: Soldering (including resistance to soldering heat).
U: Terminal strength (of components).
V: To be determined (originally assigned to "noise", but "noise-induced vibration" will be =Test Fg, one of the "Vibration" series) W: To be determined.
Y: To be determined.
See editor's footnote.
The letter X is used as a prefix in conjunction with another capital letter to designate newly added test methods. For example, Test XA: Immersion in Cleaning Agent. The letter Z is used to designate comprehensive tests and combination tests. The method is as follows: Z is followed by a short slash and the capital letter associated with the comprehensive test or combination test, for example, Test Z/AM: Combined Low Temperature and Low Air Pressure Test. Any test may be designated "Primary for Components" or "Primary for Equipment" if appropriate. 1.4 In order to further expand the test items within the test series and maintain consistency in the description, each item can be divided into details, indicated by adding another lowercase letter, for example: Test U: Strength test of lead-out terminals and integral mounting parts Ua: subdivided into tests Uai: tension and Uaz: thrust test Ub: bending
test Uc: torsion
test Ud: torque
This method can be used even if there is only one test method in the relevant series and there is no plan to develop other test methods for the time being. * Editor's note: The safety guidance function of the "mechanical strength" test has been assigned to Subcommittee 50A, and the corrosion test has been assigned to Subcommittee 50B. 6
GB/T 2421-1999
To avoid confusion with numbers, the letters i, I, 0 and ○ are not used. 2 Scope
This standard includes a series of environmental test methods and their severity levels in GB/T2421~2424, and specifies various atmospheric conditions for measurement and testing, which are used to evaluate the working ability of samples in the expected transportation, storage and various use environments. This standard is mainly for electrical and electronic products, but it is not limited to this. It can also be used in other fields when necessary. Other environmental test methods dedicated to individual types of test samples can be specified in relevant specifications. 3 Purpose
This series of standards provides a series of unified and reproducible environmental (mainly climate and mechanical strength) test methods for product specification makers and product testers, and includes standard atmospheric conditions for measurement and testing. These test methods are based on existing international engineering experience and appraisal opinions, and are mainly used to provide the following performance information of samples: a) Ability to work within the specified limits of various environmental factors (such as temperature, pressure, humidity, mechanical stress, etc.) and their combinations: Note: GB/T4796 stipulates "environmental parameter classification and severity classification"; GB/T4997 stipulates "natural environmental conditions" and GB/T4798 stipulates "application environmental conditions".
b) Ability to withstand storage and transportation conditions.
The test methods of this series of standards can be used to compare the performance of sampled products. In order to assess the quality or effective life of products in a given production batch, these methods should be used in accordance with the corresponding sampling plan. If necessary, they can also be supplemented with appropriate auxiliary tests. In order to provide tests suitable for different environmental conditions, some test procedures have many severity levels, which are obtained by changing time, temperature, air pressure or some other determining factors alone or in combination. This standard should be used together with the test methods specified in the relevant specifications, the severity level required for each test, the test sequence, and the allowable performance limit (when necessary).
4 Definitions
The tests covered in this standard consist of a series of operations in order to determine the effect of a test or a series of tests on a sample. This standard uses the following terms.
4.1 Test
A test refers to a complete series of operations, which usually includes the following items if necessary: a) pretreatment;
b) initial test;
c) conditioning test;
d) recovery;
e) final test.
1 Intermediate tests may be required during conditioning tests and recovery. 2 When the temperature and humidity measured during the sample conditioning test are the same as the temperature and humidity specified for the pretreatment, the pretreatment and conditioning tests can be combined, and the pretreatment test can replace the conditioning test test.
4.1.1 Pre-conditioning
Treatment of the test sample before conditioning testing in order to eliminate or partially eliminate the effects previously experienced by the test sample. Note
1 If pre-conditioning is required, it is the first step in the test procedure. 2 Pre-conditioning allows the sample to be subjected to the climatic, electrical or other conditions required by the relevant specifications in order to stabilize the performance of the test sample before inspection and testing. 4.1.2 Conditioning
GB/T 2421 - 1999
Expose the test sample to the test environment to determine the effect of these conditions on the test sample. Note: The definition of conditioning test (to be measured) is shown in 4.15. 4.1.3 Recovery
Treatment performed after conditioning test and before final inspection to stabilize the performance of the test sample. 4.2 Specimens
Specimens of the product to be subjected to environmental testing, including any auxiliary components and systems that make the product fully functional, such as cooling, heating and mechanical shock absorbers (isolators).
4.3 Heat dissipating test sample hcat-dissipatingspecimen Test sample with a temperature difference of more than 5℃ between the hottest point temperature on the surface and the ambient temperature measured after temperature stabilization under the atmospheric pressure specified by the free air condition and the standard atmospheric condition for the test (86kPa~106kPa). Note: In order to prove that the test sample is non-heat dissipating, the measurement can be carried out under the standard atmospheric conditions for measurement and test, but care must be taken not to affect the measurement due to external factors (such as ventilation and sunlight). For large or complex samples, it is necessary to measure several points. 4.4 Free air conditions free air conditions Conditions in an infinite space, in which the movement of air is only affected by the heat dissipating test sample itself, and the energy radiated by the test sample is completely absorbed by the surrounding air.
4.5 Relevant specification A set of technical requirements to be met by the test sample and the detection method used to determine whether these requirements are met. 4.6 Ambient temperature ambienttemperature Air temperature defined according to the following two situations. Note: When applying these definitions, guidance should be sought from GB/T2424,1. 4.6.1 Ambient temperature of non-heat dissipation test sample The air temperature around the non-heat dissipation test sample. 4.6.2 Ambient temperature of heat dissipation test sample
The temperature of the air around the heat dissipation test sample where its heat dissipation effect can be ignored under free air conditions. Note: In fact, the ambient temperature is the average of several temperatures above a horizontal plane 0mm to 50mm below the test sample, and at the same distance from the test sample and the test chamber wall or at 1㎡ from the test sample, the smaller of the two. Appropriate measures should be taken to prevent thermal radiation from affecting the measurement of these temperatures.
4.7 Surface temperature (case temperature) surfacetemperature (casetemperature) The temperature measured at a specified point (one or more) on the surface of the test sample. 4.8 Thermal stability
The state when the difference between the temperature of each part of the test sample and its final temperature is within 3℃ (or other values specified in relevant specifications). Note
1 The final temperature of the non-heat dissipation test sample is the average temperature of the test chamber where the test sample is placed at that time. The final temperature of the heat dissipation test sample needs to be repeatedly measured to determine the time interval for the temperature change of 3℃ (or other values specified in relevant specifications). When the ratio of two adjacent time intervals is greater than 1.7, it is considered that the thermal stability state has been reached.
2 When the thermal time constant of the test sample is less than the duration of exposure at a given temperature, no measurement is required; when the thermal time constant of the test sample is of the same order of magnitude as the exposure duration, an inspection should be carried out. a) Whether the non-heat dissipation test sample is within the required range of the average ambient temperature. b) For the heat dissipation test sample, repeatedly measure the time interval required for the temperature change of 3℃ (or other values specified in relevant specifications) to determine whether the ratio of two adjacent time intervals is greater than 1.7.
GB/T2424.1 provides relevant information on heat dissipation test samples and non-heat dissipation test samples. 3 In practice, it may not be possible to directly measure the internal temperature of the test sample. In this case, some other parameters that have a known functional relationship with the temperature can be measured for inspection.
4.9 ChamberbzxZ.net
GB/T 2421 - 1999
refers to a closed body or space, a part of which can reach the specified test conditions. 4.9.1 Working space The part of the test chamber (room) that can maintain the specified test conditions within the specified tolerance range. 4.10 Combined test
A test in which two or more test environments act on the test sample at the same time. Note: Measurements are usually taken at the beginning and end of the test. 4.11 Composite test A test in which the test sample is exposed to two or more test environments in sequence. Note
The time interval between each exposure may have a significant effect on the test sample and should be accurately specified. 1
2 Generally, no pretreatment, recovery and stabilization are performed between each exposure. 3 Testing is usually carried out before the first exposure and after the last exposure. 4.12 sequence of tests the order in which the test specimens are exposed to two or more test atmospheres. NOTES
1 The time interval between exposures does not normally have a significant effect on the test specimens. 2 Preconditioning and recovery are normally performed between exposures. 3 Tests are normally performed before and after each exposure, the final test of the previous exposure being the initial test of the next exposure. 4.13 reference atmosphere reference atmosphere atmospheric values measured under any conditions are corrected by calculation. 4.14 referee measurements repeated measurements made under precisely controlled atmospheric conditions when the correction factors used to adjust atmospheric parameters sensitive to the reference atmosphere are not satisfactory and when measurements made within the recommended range of ambient atmospheric conditions do not give satisfactory results. 4.15 conditioning the process of exposing the test specimens to atmospheric conditions of specified relative humidity or completely immersed in water or other liquid at a specified temperature for a specified period of time. NOTE The space used for conditioning tests may be the entire laboratory (where the specified conditions are maintained within specified tolerances) or a special test chamber, depending on the actual situation.
5 Standard atmospheric conditions
5.1 Reference standard atmospheric conditions
Temperature: 20℃;
Air pressure: 101.3kPa (1013mb)
Note: Since relative humidity cannot be corrected by calculation, it is not specified. If the parameter to be measured varies with temperature or air pressure, and the law of its variation is known, the parameter value shall be measured under the conditions specified in 5.3. If necessary, it can be corrected to the above-mentioned reference standard atmospheric parameter value by calculation. 5.2 Standard atmosphere for arbitration measurement and test
If the law of variation of the measured parameter with temperature, air pressure and humidity is unknown, one of the standard atmospheric conditions for arbitration measurement and test listed in Table 1 shall be selected by agreement for measurement.
Normal value
Temperature,
Smaller tolerance
Larger tolerance
1) Range value including the first and last two items. Note
GB/T 2421
Standard atmosphere for arbitration measurement and test
Relative humidity\,%
Narrow range
125℃ is mainly used for semiconductor device and integrated circuit testing. Wide range
60-~70
2 Smaller tolerances can be used for arbitration measurements. Larger tolerances can only be used when relevant specifications allow. 3 Relative humidity can be ignored when it does not affect the test results. 5.3 Standard atmospheric conditions for measurement and testing
5.3.1 The range of standard atmospheric conditions for measurement and testing is shown in Table 2. Table 2 Standard atmospheric conditions for measurement and testing
Temperature1
15℃~35℃
1) The range of values including the first and last two items. 2) Absolute humidity ≤ 22g/m2
Relative humidity 112
25%~75%
86~106
86-~106
86～106
(860~1 060)
(8601 060)
(860~1 060)
Air pressure"
86 kPa~106 kPa
(860 mb--1 060 mb)
1 The changes in temperature and relative humidity during the series of measurements made as part of the sample test shall be kept to a minimum. 2 For larger samples or where it is difficult to maintain the temperature within the test chamber within the above specified range, the range may be appropriately relaxed when permitted by the relevant specification, with a lower limit of 10°C and an upper limit of 40°C.
5.3.2 If the relevant specification considers that it is impractical to measure under these standard atmospheric conditions, the actual conditions of the measurement shall be recorded in the test report.
Note: Relative humidity may be ignored if it has no effect on the test results. 5.4 Recovery conditions
After the conditioning test and before the final measurement, the test sample shall be stabilized at the ambient temperature at the time of the measurement. When the electrical parameters of the test sample are affected by moisture absorption or surface condition and change rapidly (for example, the insulation resistance increases significantly within about 2 hours after the sample is removed from the humidity chamber), the "controlled recovery conditions" specified in 5.4.1 of this standard should be used. ". When the electrical parameters of the test sample do not change quickly due to moisture absorption or surface conditions, the recovery can be carried out under the test standard atmospheric conditions specified in 5.3 of this standard.
When the recovery and measurement are not carried out in the same test box (room), the indoor temperature and humidity conditions should be such that no condensation will appear on the sample surface when the test sample is transferred to the measurement box (room). The recovery conditions and duration are specified in most test methods of GB/T2423. Unless otherwise specified in the relevant specifications, the conditions specified in GB/T2423 should be used.
5.4.1 Controlled recovery conditions
The controlled recovery conditions are as follows:
Temperature: actual test room temperature ±1°C, but within the range specified in 5.3, that is, between 15°C and 35°C; Relative humidity: 73%~～~77%;
Air pressure: 86kPa~106kPa (860mb~1060mb); GB/T 2421-- 1999
Recovery time: If it is different from the provisions of GB/T2423, it should be specified in the relevant specifications. In specific cases, if different recovery conditions are required, the relevant specifications should specify them. Note: Controlled recovery conditions can also be used for pretreatment. 5.4.2 Recovery procedure
Conditional test Within 10 minutes after the test, place the test sample in the recovery box. (If the laboratory environmental conditions permit, the sample can be placed in the laboratory for recovery) If the relevant specifications require immediate measurement after recovery, the measurement should be completed within 30 minutes after the test sample is taken out of the recovery box, and the parameters that change the fastest should be measured first. The difference between the temperature in the recovery box and the laboratory temperature should not exceed 1C to prevent the test sample from absorbing moisture or drying when it is taken out of the recovery box. The recovery box must have good thermal conductivity and can strictly control the humidity in the box. 5.5 Standard drying conditions
5.5.1 If the test sample is required to be dried before measurement, it should be dried for 6 hours under the following conditions unless otherwise specified in the relevant specifications. Table 3 Standard drying conditions
55℃+2℃
1) Range values including the first and last two items. Relative humidity
Air"
86 kPa~106 kPa
(860mb~1060mb)
5.5.2 If it is difficult to dry under standard drying conditions, the actual drying conditions should be recorded in the test report. 5.5.3 When the specified high temperature test temperature is lower than 55C, a lower temperature should be used for drying. 6 Application of test methods
These test methods can be used for type testing, identification testing, quality inspection testing or any related purposes in accordance with the relevant specifications. 7 Climate test sequence
The sequence of climate tests is mainly applicable to various types of components. In order to use them when required, it is generally believed that there is a certain connection between low temperature, high temperature, low pressure and alternating damp heat tests, and it is called the climate sequence. The order of conducting these tests is as follows: high temperature;
Alternating damp heat (the first cycle of test Db with an upper limit temperature of 55C); low temperature:
Low pressure (when required);
Alternating damp heat (the remaining cycles of test Db with an upper limit temperature of 55℃ ). The time interval between these tests should not exceed 3 days, except for the time interval between the first cycle of the alternating damp heat test and the low temperature test, which time interval including the recovery time should not exceed 2 hours. Measurements are usually only carried out at the beginning and end of the climate sequence, unless otherwise specified.
8 Climate classification of components
When climate classification is used for components, it should be based on the general principles in Appendix A. 9 Application of tests
9.1 The relevant specification should specify whether the test should be carried out under "power on" or "power off" conditions. If the shipping box is considered to be part of the sample, the relevant specification may also specify that the "packaged" sample be tested when necessary. 9.2 When the test sample is too large or too heavy to be tested with the entire sample, the main components can be tested separately, and the relevant specification should give details of the test method to be adopted
Note: This method is only applicable to components that do not affect each other unless these effects can be taken into account. 10 Numerical meaning of the value
GB/T 2421 —1999
In (GB/T2423 environmental test methods, quantitative values of various test parameters (temperature, humidity, stress, duration, etc.) are provided. These values can be expressed in different ways according to the requirements of each test. The two most commonly used cases are:
a) expressed as a nominal value with tolerance.
b) expressed as a range of values.
For these two cases, the meaning of the values is discussed as follows: 10.1 Nominal value with tolerance
Two examples of expression are as follows:
a) (40±2)C;(2±0.5)se
b) (93 +2)%.
The significance of expressing quantitative values as nominal values with tolerances is that the test should be carried out at the specified value. The specified tolerances are mainly considered in the following aspects:
a) It is difficult for the test equipment adjustment device to accurately adjust the test parameters to the specified value, and this adjustment value will drift during the test;
b) Instrument error:
c) In the space where the test sample is placed (no special tolerance is specified), the environmental parameters are not uniform. The purpose of specifying tolerances is not to allow the parameter values in the test space to be adjusted within this range. Therefore, when the quantity is expressed as a nominal value with a tolerance, the test device should be adjusted to the nominal value to take into account the instrument error. In principle, even if the test equipment error is so small that it can be ensured that the limit value is not exceeded, the test equipment should not be adjusted to and maintained at the limit value.
For example: if the quantitative value is 100 ± 5, the test equipment should be adjusted and maintained at the ear mark value of 100, taking into account the instrument error, and should never be adjusted and maintained at the target value of 95 or 105. Note
1 In order to avoid the test sample exceeding any limit during the test time, it is necessary to adjust the test equipment to a certain tolerance limit in some cases. 2 In special cases, when a quantity is expressed as a nominal value with a unilateral tolerance (generally speaking, it is not recommended to express it unless these special cases are justified), taking into account the measurement inaccuracy, the test device should be set to the nominal value (which is also a tolerance limit) as accurately as possible, depending on the equipment used for the test (including the instrument measuring these parameter values). For example: If the quantity is expressed numerically as 100 °C, and the total uncertainty of the test device can control the parameter within ±1, then adjust the test device to maintain the target value at 99. On the other hand, if the total uncertainty is ±2.5, then the target value should be maintained at 97.5. 10.2 Quantitative value expressed in numerical range
For example:
(15～35)C;
.Relative humidity (80～100%;
-1h~2 h.
Note: The numerical range indicates the value, which may cause misunderstanding. For example, "80%~100%" is considered by some to exclude the values of 80 and 100, while others are considered to include the value. Using symbols such as \>80 or ≥80" can usually reduce misunderstandings and should be used first. The significance of expressing the value in a numerical range is to indicate the value to which the test equipment is adjusted, which has little effect on the test results. If the inaccuracy of parameter control (including instrument error) is allowed, any expected value within the given range can be selected. For example, if the temperature is specified to be 15C~35C, any value within the range can be used (but it should not mean that the temperature should be varied within the entire range). In fact, the intention of the test method writer is that the test should be carried out at normal ambient temperature. 12
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