Some standard content:
Machinery Industry Standard of the People's Republic of China
Switches for Electric Blankets and Similar Purposes
This standard adopts IEC10581 (1990) "General Requirements for Appliance Switches Part 1". 1 Subject content and scope of application
JB 621192
This standard specifies the classification, structure, performance and safety requirements for switches for electric blankets and similar purposes, as well as the corresponding test methods and inspection rules.
This standard applies to the temperature-regulating and non-temperature-regulating soft wire control switches of electric blankets, electric mattresses, electric quilts, electric heating pads, and electric heating caps, electric vests, electric stomach protectors, electric heating insoles and other electric heating appliances (hereinafter Referred to as switch). This standard does not apply to power switches and temperature switches of electric heating appliances that use electric heating wires as heating elements that are not in direct contact with the human body, as well as switches that require DC polarity markings. 2 Reference standards
National standard
Appliance switches Part 1 General requirements GB4706.1 General safety requirements for household and similar electrical appliances Special safety requirements for household and similar electrical appliances Electric blankets, electric heating pads and electric heating mattresses Requirements GB 4706.8 | | tt | | GB8278 | | tt |
GB 4208
GB 2828
GB 2829
GB 4206
Industry standard
3 terms
Electrical accessories , Controller and protector terminology Classification of enclosure protection levels
Batch-by-batch inspection and counting sampling procedures and sampling tables Periodic inspection and counting sampling procedures and sampling tables Identification of electrical terminals and general rules for marking terminals with alphanumeric symbols Appliances In addition to the terminology of switches
, in addition to complying with GB10964 and the industry standard "Terminology of Appliance Switches" and the relevant national terminology standards, the terms in this standard are supplemented as follows.
3.1 cord-grip
A device installed at the outlet of the switching power cord and external flexible cord to prevent the power cord from being pulled out. 3.2 Temperature adjustment and shutdown switchwith temperature regulator is a switch that adjusts the temperature of electric heating appliances by changing the power of the electric heating load. It can be adjusted in steps or continuously. 3.3 Constant temperature switch is a switch that controls the on and off of the control element in the switch through a temperature sensitive element placed in the electric heating appliance, so that the temperature of the electric heating appliance is automatically maintained at a fixed set value.
3.4 ??Temperature control switch switch with temperature controller is a switch that can adjust the temperature of the electric heating appliance and automatically keep it constant at the corresponding temperature according to the signal of the temperature sensitive element placed in the electric heating appliance. It can be multi-gear adjustment or stepless continuous adjustment. Approved by the Ministry of Mechanical and Electronic Industry on 1992-06-16 34
1993-01--01 implementation
3.5 push-pull switch toggle switch
JB 6211-92
By dial A small switch that moves the contacts to maintain one of two or more states of the circuit. 4Basic parameters
4.1 The maximum working voltage of the switch is divided into: 42, 130, 250V; the rated voltage of the switch is divided into: 36, 110, 220V. 4.2 The rated current priority values ??of the switch are: 0.5, 1, 2, 4, 6, (10) A. 5 categories
5.1 Product classification
5.1.1 According to protection against electric shock:
8. For Class II appliances,
b. For use in Class III appliances.
5.1.2 According to the protection level: protection against solid foreign objects larger than 1.0mm (IP4X). 5.1.3 According to the type of circuit load controlled by the switch: suitable for basic resistive load circuits with a power factor not less than 0.95. 5.1.4 According to the number of operation cycles: 10,000 times. 5.1.5 According to the ambient air temperature of use: - 25℃~55℃. 5.1.6
a.
b.
5. 1. 7
5. 1. 8
5.1.9
Classification by terminal blocks:
Terminal blocks in which the ends of power cords and external cords are not specially prepared and can be connected without using any special tools. The ends of power cords and external cords require specially prepared terminal blocks that can be wired without the use of any special tools. According to the environmental pollution level applicable to the switch without additional protection conditions: switch suitable for normal state. According to heat resistance and fire resistance: Class D switch.
According to the degree of moisture resistance: unprotected switch (IPX0). 5.1.10
a.
b.
According to the connection method:
bipolar switch;
bipolar multi-position switch.
5.1. 11
According to the nature of the power supply:
a.
b.
c.
AC switch; ||tt ||DC switch;
AC/DC switch.
5.2 model preparation method
5.2.1 model
5.2.2 characteristics
R□OO
symbol
x||tt ||x
Variety (according to Article 5.2.4)
Type (according to Article 5.2.3)
Specification code (switch rated current value in A) design Code (1~5 Arabic numerals)
Feature code (according to 5.2.2)
Category code (indicating soft wire switch)
35
a.
Push switch U
b.
Rotary switch Z
5.2.3 type
Ordinary switch P
a.|| tt||b.
Temperature control switch T
Temperature control switch K
c
d.
Thermostatic switch H
5.2 .4 varieties
stepless continuous adjustment switch [
a.
JB 6211- 92
b． Multi-gear adjustment switch (depending on the number of adjustable gears, represented by 2, 3, 4...) 6 Technical requirements and test methods
6.1 Basic requirements
6.1.1. The switch shall be manufactured according to the drawings and technical documents approved by the prescribed procedures and shall comply with the provisions of this standard. 6.1.2 The switch should be safe and reliable during normal use. Even if there is reckless use that may occur during normal use as allowed in this standard, it will not cause danger to people or the surrounding environment. Compliance with the requirements of Articles 6.1.1 and 6.1.2 is checked by carrying out all type tests specified in this standard. 6.2 Environmental conditions
The altitude does not exceed 2000m;
a.
The ambient air temperature is not higher than 55℃ and not lower than 25℃. b.
The relative humidity of the air is not greater than 85% (at a temperature of 25°C); c.
In a medium without explosion hazard, and there are no gases and gases in the medium that are sufficient to corrode metal and destroy insulation. Dust; d.
In places with ineffective strong vibration and impact;
e.
f.
In places where there is no snow or rain or water cannot get wet . 6.3 Performance
6.3.1 Electronic temperature control switches and temperature control switches should be able to work normally at 1.1 times and 0.85 times the rated voltage. The switch is connected to the load according to normal use conditions, and an ammeter with an accuracy of not less than level 1 is connected in series to the power circuit. Full adjustments are made 10 times at 1.1 times and 0.85 times the rated voltage. Observe the ammeter. It should be at 1 of the switch. . Uniform changes within 1 times the rated current range should not cause flash points or breakpoints. After the test, the switch should not be faulty or damaged, and the indicator light of the switch should be able to provide normal instructions. 6.3.2. Under rated voltage and rated load, the temperature control switch should conveniently and reliably adjust the temperature of the electric heating appliance within the temperature adjustment range specified by the switch. The constant temperature error of the switch should not be greater than 3°C. The switch is connected to the load according to normal use conditions, and four measuring points are evenly spaced within the adjustment stroke of the switch. Connect a voltmeter with an accuracy of not less than level 1 in parallel to the output end of the switch. First, stabilize the electric heating appliance at the maximum or minimum point among the four measurement points for 3 hours, and then measure the temperature of the electric heating appliance at each point in turn.
Observe the condition of the voltmeter. After the switch has been turned on and off at least three times at each measuring point, measure the temperature t2 of the electric heating appliance at the moment the switch is turned off and the temperature ti, t2 and the moment it is turned on. The difference between ti should not be greater than 3℃. 6.3.3 The thermostatic switch is connected to the load according to normal usage conditions. Power on for 3 hours at 1.1 times and 0.85 times rated voltage respectively. The switch should work properly and the indicator light should provide normal indication. The temperature of the electric heating load should be within ±1°C of the rated temperature stability value of the switch. The temperature measurement methods in Articles 6.3.2 and 6.3.3 shall be in accordance with the relevant provisions of Article 11.3 of GB4706.8. 6.4 Structure
6.4.1 Safety structural requirements of the switch during normal operation 6.4.1.1 The combined assembly of the cover and bottom of the switch must fit well and be fastened, and it is impossible to displace or displace it without using tools. Remove. Cover and bottom fasteners should not be used to fasten any other parts except the actuator. When tightening the fastening screws, it is not allowed to damage the insulation and electrical parts. The fastening screws of the cover and bottom should not be easy to fall off. Compliance is checked by observation and manual inspection. Note: ① It is considered that two unrelated fasteners will not loosen at the same time. ② Parts fastened with screws or nuts equipped with tightening washers are considered not easy to loosen as long as these screws and nuts do not need to be disassembled during normal use and maintenance by the user.
③ If springs and elastic parts do not loosen and fall off during the tests of Articles 6.12 and 6.13, they are considered to be difficult to loosen and fall off. 6.4.1.2 The power lead port and cord outlet of the cord switch should be protected by protective sleeves made of heat-resistant soft rubber or plastic and other insulating materials to prevent the cord from excessive bending at the outlet and inlet of the switch. The protective sleeve should fit well with the switch housing and be designed to prevent pulling and loosening. The length of the sheath extending beyond the outside of the switch shall be at least five times the outer diameter of the narrow side of the cord. 6.4.1.3 The switch must have a wire clamping device made of insulating material so that the wires connected inside the switch are not subject to tension or torque, and at the same time, the outer cladding of the wires is protected from scratches.
Test Articles 6.4.1.2 and 6.4.1.3 by observing, measuring and passing the tests specified in Articles 25.101.5 and 25.101.6 of GB4706.8.
6.4.1.4 For switches with power cords and external cords, the wire material and nominal cross-sectional area shall comply with Article 25.6 of GB4706.1.
Determine compliance by inspection and measurement. 6.4.1.5 For switches with power supply cords and external cords, the length of the cord at the plug end and the length of the cord at the load appliance end shall comply with the provisions of Article 4.2.2 of GB8278 or the user's requirements. Check by measuring.
6.4.1.6 The operating part of the switch should be reliably fixed and cannot be removed without the use of tools. Check through the following test.
Let the actuator withstand an axial tension of 30N for 1 minute. If the shape of the actuating part prevents it from being pulled during normal use, the actuating part is subjected to an axial pulling force of 15N for 1 minute.
After the test, the knob should not come out and the switch should still be usable. 6.4.2 Electrical structure of the switch
6.4.2.1 Both non-adjustable switches and adjustable switches should be bipolar fully disconnected structures. The opening distance when the contacts of each pole are disconnected shall not be less than the requirements in Table 2.
6.4.2.2 The rated current value of the contact capacity of each gear of the non-electronic multi-position temperature regulating switch should be the same. Check 6.4.2.1 and 6.4.2.2 by hand test and observation. 6.4.2.3 The switch should have a light display that can reliably indicate the closed position and the open position. The indicator light of the temperature adjustment and temperature control switch should be on at each adjustment position of the switch, and should only go out when the switch is in the off state. After the switch is turned on, the indicator light should not go out due to the normal and fragrant operation of the electric heating load.
6.4.2.4 When the position of the actuator is used to indicate the contact position or temperature adjustment level, there should be obvious signs of "on", "off" and temperature levels corresponding to it. The position mark of the actuator should correspond to the position of the contact. The representation method can be Chinese characters, English letters or symbols. If represented by English letters or symbols, the open position is represented by "OFF" or "0" (a circle), and the closed position is represented by "ON" or "1" (a straight line). Other temperature positions are represented by "1", "2", "3" or colored symbols.
Check compliance with the requirements of Articles 6.4.2.3 to 6.4.2.4 by hand test and observation. 6.4.2.5 The creepage distance and electrical clearance of the switch are reduced due to wear, but they should not be lower than the values ??specified in Article 6.14. The structure of the switch shall be such that if any conductive part of the switch becomes loose and falls out of its position, it is unlikely in normal use that the creepage distance or electrical clearance across supplementary insulation or reinforced insulation will be reduced to the value specified in Article 6.14 below 50%. Tested by observation, measurement and hand testing. 6.4.3 Appearance
37
JB 6211-92
The surface of insulation parts and plastic parts should have good gloss and be free of pollution, bubbles, cracks, lack of material, swelling, and obvious Defects such as deformation or shrinkage, scratches and burrs.
Check compliance by observation.
6.5 Mechanism
6.5.1 The mechanism of the switch should prevent the contacts from staying in any position between making or breaking. Note: The mechanism of the multi-position switch should prevent the contact from staying in any position between two adjacent positions. 6.5.2 The mechanism of the switch should make it impossible to accidentally change the adjusted position. If the operating part of the switch fluctuates slightly up, down, left and right, the switch should not have poor contact. When the switch is in the off position, it should not be removed from the off position due to falling or unintentional touching. Check whether it complies with the requirements of Articles 6.5.1 and 6.5.2 by hand test. During the test, the operating parts are operated according to normal use. 6.5.3 The manual multi-stage temperature control switch should have obvious gears, easy adjustment, sensitive and reliable action, and the operating force of the operating part should comply with: a. Push switch: 9~12 N;
b． Knob switch: 0.2~0.3 N·m. Use a tube dynamometer and wrench with Level 2 accuracy for measurement. 6.6 Electric shock protection
6.6.1 The switch's casing, operating parts and other easily accessible parts should be made of insulating materials. Test by observation.
6.6.2 Insulating materials must be high temperature resistant, non-deformable and flame retardant. Verified by the test specified in 6.15. 6.6.3 When the switch is operated in normal use and in any position, it shall have adequate protection against contact with the live parts of the switch and metal parts separated from the live parts by basic insulation only, or the basic insulation itself. Compliance is checked by observation and by the following tests. When the switch is in normal use, remove any removable parts and test every possible part with the test pins shown in Figure 1. Do not touch exposed live parts and metal parts that are isolated from live parts by basic insulation only. It is best to use a light bulb as an electric contact indicator, with a voltage of not less than 40V.
20
200
生
0-92
4／ 15o
sg=8
Q|| tt||Figure 1 Test Pin
6.7 Terminals
6.7.1 Switches with a rated current exceeding 1A should not be connected to the power cord by soldering, spot welding, pressing or similar methods. 6.7.2 Flexible wires that have not been specially prepared should not be connected to the switch by soldering, spot welding, pressing or other similar methods. 6.7.3 If the rated current of the switch is less than or equal to 3A, its terminals should be allowed to connect flexible wires with a nominal cross-sectional area of ??0.5~0.75mm2. If the rated current is greater than 3A, its terminals should allow the connection of flexible wires with a nominal cross-sectional area of ??0.75 ~ 1mm. Articles 6.7.1 to 6.7.3 are tested by observation and measurement. 6.7.4 The requirements and test methods of various types of terminal blocks must comply with the relevant provisions of Article 6.4 of the national standard "General Requirements for Appliance Switches Part 1".
6.8 Protection against solid foreign objects and moisture-proof
38
6.8.1 Protection against solid foreign objects
JB 6211—92
Inspected through the corresponding tests specified in GB4208 . If the corresponding test rod cannot enter the switch, the protection requirements are met. All removable parts should be removed during testing. 6.8.2 Moisture-proof
switches should be able to withstand damp conditions that may occur during normal use. Check through the following test.
The cable entry holes of the switch must be opened, and the detachable parts must be removed. If necessary, they should be subjected to moisture treatment together with the switch body. Humidity treatment is carried out in a humidity chamber. The relative humidity of the air in the box is between 91% and 95%, and the temperature is maintained at 30±1°C. The air in the box must be continuously circulated.
Before placing the sample in the humidity chamber, it should be placed in an environment with a temperature between 30 and 35°C for at least 4 hours. The sample is kept in the box for 2d (48h). After the humidity treatment, reassemble the detachable parts and immediately conduct the tests in Articles 6.9.1 and 6.9.2 in a humidity box or indoors with a temperature of 30 ± 1°C. There should be no damage to the switch after the test.
6.9 Insulation resistance and dielectric strength
6.9.1 The insulation resistance of the switch should not be lower than the value specified in Table 1. Check by the following measurements.
Immediately after the moisture treatment in Article 6.8.2, measure the insulation resistance. Measure after applying about 500V DC voltage for 1 minute. The insulation resistance of each part of the switch should not be lower than the value specified in Table 1. Use an insulation resistance meter (megohmmeter) with a DC voltage of 500 ± 50V for measurement. 6.9.2 The switch shall have sufficient dielectric strength. Immediately after the test in Article 6.9.1, the following withstand voltage test shall be carried out. Each part of the switch is subjected to 50Hz, actual sinusoidal waveform, and test voltage specified in Table 1 for 1 minute. Initially, a voltage less than half the specified value is applied and then rapidly increased to the full value. No flashover or breakdown should occur during the test, and glow discharge without voltage drop is ignored. Table 1
Insulation resistance
Tested part
When the switch is in the "on" position, between all stages connected together and the shell
The switch is in the "on" position When the switch is in the "on" position between the two disconnected points of each stage, 1
minimum value
Ma||tt| |7
7
5
Dielectric strength test voltage
V
Operating voltage
≥50
3750
2000
2000
working voltage
50
500
500
500
Note: ① Wrap the metal foil to a point 10mm longer than the cord sheath. The metal box should not be pressed into the opening, but it must be pushed into the corner or similar position with a standard test finger to make the metal foil fit tightly along the outer surface of the switch. ② For high-voltage test transformers, when the output terminal is the test voltage, the short-circuit current at the output terminal is at least 200mA. When the output current is adjusted to less than 100mA, the overcurrent relay should not trip. The deviation of the effective value of the test voltage should be within 3%. 1) For special components connected to the switch circuit, such as lamps, coils, capacitors or electronic components, one pole may be disconnected (or short-circuited) as appropriate. 6.9.3 The electronic components in the switch that provide a current path for the load should be able to withstand 400V DC and have a reverse withstand voltage of 1 minute without damage. During the test, one or both ends of the electronic component may be disconnected from the circuit if appropriate, and the component may be tested separately. 6.10 The heating test requirements and methods of the heating
switch are in accordance with Article 6.9 of the national standard "Part 1 General Requirements for Appliance Switches". The test environment temperature is 25±2℃.
39
JB 6211-- 92
The test sample of the switch is placed on the test platform specified in Article 2.2.29 of GB4706.8 for testing. The temperature rise of each part of the switch should meet the following requirements: the shell ≤ 35K | | tt | | terminal block ≤ 45K | | tt | The provisions of Table 11 in "General Requirements for Switches Part 1".
6.11 Durability
According to the relevant provisions of Article 6.11 of the national standard "General Requirements for Appliance Switches Part 1". Each circuit controlled by the switch should be loaded according to the specified rated load value and tested in a non-inductive circuit. The switch is tested in an environment of 25±5℃. After the test, the switch should meet the following requirements: all actions are still reliable, and the indicator lights and electronic components can still work normally; a.
b. The sample shall be tested in accordance with the provisions of Article 6.10, and the temperature rise of the terminal shall not exceed 55K; the C sample shall no longer be subjected to moisture treatment and shall be able to withstand the withstand voltage test specified in Article 6.9.2, but the test voltage drop shall be as specified in Article 6.9.2 75% of the specified value.
6.12 Mechanical strength
6.12.1 According to the requirement 6.12.2 in the national standard "General Requirements for Appliance Switches Part 1". 6.12.2 Drop test
In the rolling chamber as shown in Figure 2, the switch without wires must be connected to a switch as specified in Article 25.6 of GB4706.1, with a minimum nominal cross-sectional area and free For a flexible cord with a length of 50 mm, tighten the terminal screws with two-thirds of the torque specified in sub-clause 6.13. Switches with conductors shall be tested in the condition as delivered. Cut the cord to about 50mm. The sample is dropped from a height of 500mm onto a steel plate with a thickness of 3mm. The number of drops is: N
A
3mm
steel plate
30
130
40
250
Figure 2 Roll simplified
AA profile
JB 6211-92
If the mass of the sample does not exceed 100g, the number of drops is 1000 times; if the mass of the sample exceeds 100g but does not exceed 200g when the cord is not connected, the number of drops is 500 times; if the cord is not connected, the number of drops is 500 If the mass exceeds 200g, the number of drops is 100 times. The roller rotates at a speed of 5r/min, so that 10 drops can occur per minute. Only one specimen is in the drum for each test. After the test, the specimen shall not show damage within the meaning of this standard. In particular, no parts should become detached or loose. Pay special attention to the connection of the soft cord.
If the protective measures against electric shock are not affected, small pieces may fall off and operating parts may be damaged without being judged as unqualified. 6.13 Screws, current-carrying parts and connecting parts
According to the relevant provisions of Article 6.13 of the national standard "Part 1 General Requirements for Appliance Switches". 6.14 Electrical clearances, creepage distances and insulation penetration distances 6.14.1 Electrical clearances and creepage distances shall comply with the provisions of Table 2. Table 2
Tested part
Between live parts of different polarities
Completely disconnected contact ends
Reinforced insulation
50| |tt||Creepage distance
2.0
2.0
The measurement method is in accordance with the national standard "Appliance Switches Part 1 Electrical Room
1.5
2.0||tt ||Operating voltage
V
>50～130
Creepage distance
2.0
3.0
8.0
Electrical clearance
1.8
3.0
6.0
The provisions of Appendix D in General Requirements.
mm
>130～250
Creepage distance
3.0
3.0
8.0
Electrical clearance|| tt | | 2. 0 | Measure once each without connecting wires.
Place movable parts in the most unfavorable position, nuts and other threaded parts and non-cylindrical head screws are supposed to be screwed in the most unfavorable position, and all detachable parts are removed.
Switches with wires are measured once each with and without wires connected to a specified cross-sectional area. 6.14.2 The insulation penetration distance should comply with the requirements in Table 3. Table 3
Insulation types
Basic insulation
Reinforced insulation
Additional insulation
6.15 Heat resistance, flame resistance, surface leakage tracking resistance and abnormal temperature resistance Insulation penetration distance under all working voltages 1
2
1
mm
6.15.1 Heat resistance, flame resistance and surface leakage tracking resistance test according to the national standard "Appliance Switches" Relevant provisions of Article 6.15 of Part I General Requirements. 6.15.2. The casing of the switch should be able to withstand high and low temperatures under abnormal conditions. After the switch is placed in a constant temperature box at 100°C and a constant temperature freezer at -25°C for 4 hours each, there should be no cracking, breakage, deformation, etc. After the test, the switch should be able to be used and operated normally. 6.16 Anti-rust
Iron parts that may endanger safety before rusting should have adequate anti-rust protection. Inspected through the test specified in Article 6.16 of the national standard "General Requirements for Appliance Switches Part 1". 41
7 Inspection Rules
Type Inspection
7.1 Type
7.1.1 Type test a should be carried out when any of the following situations occur.
b.
CbzxZ.net
d.
e
JB 6211-92
Trial production of new products or old products transferred to factory Formulated type identification; after formal production, if there are major changes in structure, materials, and processes, which may affect product performance; during normal production, periodic inspections should be conducted every two years; when production is suspended for more than half a year and production is resumed; || tt||When the factory inspection results are significantly different from the last type inspection: when the national quality supervision agency proposes a request for type inspection. f.
7.1.2 Type inspection includes inspection of all technical requirements specified in this standard. During the test, it was divided into three test groups. The test items and order of each group are shown in Table 4.
7.1.3 Type test sampling and judgment shall be carried out in accordance with the provisions of GB2829. The unqualified quality level (RQL) of the 1st and 3rd test groups is set to 50, the judgment level (DL) is I, a one-time sampling plan is adopted, and the judgment array (Ac, Rc) is (O, 1), that is, the two The number of samples in each test group is 1. The unqualified quality level (RQL) of the second test group is 40, the judgment level (DL) is I, a secondary sampling plan is adopted, and the judgment array (A, R; Az, R2) is (0, 2; 1, 2 ), that is, the number of specimens in the first sample and the second sample of the test group is both 3. 7.1.4 When testing the second sample of Group 2, only the unqualified items in the first sample that may affect the test results before the item can be tested. Table 4
Test items
Name
Name
Mark inspection (including rating and classification) Electric shock protection inspection
Terminal and end inspection| |tt||Structural inspection
Mechanical inspection
Performance test
Inspection against solid foreign objects and moisture proof
Insulation resistance measurement and dielectric strength test
Heat generation Test
Durability test
Mechanical strength test
Inspection of screws, current-carrying parts and connectors
Measurement of electrical rooms, creepage distances and insulation penetration distances Heat resistance, Flame resistance, surface tracking resistance and abnormal temperature resistance test
Anti-rust test
Related articles
Chapter 4, 5 and 8
Article 6.6| |tt||Article 6.7
Article 6.4
Article 6.5
Article 6.3
Article 6.8
Article 6.9||tt ||Article 6.10
Article 6.11
Article 6.12
Article 6.13
Article 6.14.1
Article 6.14.2 Article
Article 6.15
Article 6.16
Test Group
Group 1
Group 2
Group 3| |tt||Attach
Note
According to Table 1 Note 1) It may be necessary to attach
Add a set of samples
7.1.5 If the type test result is judged to be unqualified, If the cause of the failure can be corrected immediately, the products manufactured after the failure is corrected are allowed to be re-inspected for type inspection. During the inspection, there are still three test groups specified in Table 4. The first and third test groups are each composed of one sample, and the second test group is composed of three samples. The samples should be randomly selected, and the retest samples should all be qualified. . 42
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