Brief introduction of relevant standards for Temperature Humidity Chamber

1. International standards

The basic environmental test procedures are a set of environmental test standards developed by the technical committee 50 (TC 50) of the International Electrotechnical Commission (IEC) (IEC publication No. 68).

Because there are a large number of electricians and electronic products in domestic and international circulation, both users and producers are very concerned about the performance, reliability and safety of the products in storage, transportation and use, and require the establishment of common standards to ensure that the products can work satisfactorily.The Basic Environmental Testing Procedures were developed from the 1960s to the 1980s to meet this need.

This series of environmental test standards has absorbed the experience of standardization in various countries and concentrated the wisdom of experts from various countries, so it has the advantages of complete system, rigorous structure, easy to use, perfect content and so on, and is scientific and advanced, and has been widely adopted in various countries around the world.Not only electrical, electronic products, other industry products are also used.


2. United States Military Standards (MIL)

The basic standards are Mil-STD-810C environmental test methods for space and land use and MIC-STD-202F test methods for electronic and electrical parts.

The U.S. military logo, like the IEC standard, has been widely adopted internationally.

In the 1980s, China's relevant departments organized and formulated GB 2421-2424 basic environmental test regulations for electrical and electronic products, GJB 150 environmental test methods for military equipment, and GJB 360 test methods for electronic components, which are respectively equivalent to IEC 68 publication, MIL-STD-810C and MIL-STD-202F.In the 1990s, in order to improve the competitiveness of our products in the international market, the relevant state departments clearly stipulated that the test methods and standards for civil and military products should be the same as those of IEC and MIL respectively.


3. Technical conditions of environmental testing equipment

The above is the environmental test method standard, there is another kind of environmental test equipment product standard or technical conditions.

The technical conditions of well-known foreign products are as follows:

BS 3898-1965 technical conditions for laboratory hot and humid tanks is a british standard and widely used in other countries.

Astme-145-1968. technical conditions for gravity convection and forced ventilation in aging cabinets. American society for testing materials standard.

ASTMD 2436-68 "standard technical conditions for laboratory ovens for forced convection in electrical insulation" astm Standard.

IEC publication no. 216, "Guidelines for testing the heat resistance of electrical insulating materials", Part 4, ageing ovens.

China's relevant departments have also successively formulated various technical conditions of environmental test equipment, such as: GB 10586 "technical conditions of wet and hot test chamber" GB 10589 "technical conditions of low temperature test Chamber" GB 10592 "technical conditions of high and low temperature test chamber", etc.


4. Verification methods for relevant environmental testing equipment

China's relevant departments to formulate the GB 5170 "electrician and electronic product environmental testing equipment basic parameter calibration method", the HB 6783 "military airborne equipment climate environment chamber (room) verification methods, HB 7122 the civil aircraft airborne equipment climate chamber (room) verification methods, verification and certification rules-based making environmental testing equipment, the equipment quality guaranteed.


5.Temperature performance indexes in test methods and technical conditions

A. In the test method, the main index is tolerance (allowable error), and some standards also require temperature variation (temperature fluctuation degree).

"Tolerance" is stated in note IEC68-2-3, 2.1 that "the tolerance of temperature ±2 ° C is due to the consideration of absolute errors of measurement, slow temperature changes and temperature fluctuations in the workspace".

In IEC 216 publication no. 4, Oven for ageing, "temperature deviation" is defined as "temperature error due to a combination of temperature fluctuations and temperature gradients".

In MIL - STD - 810-4.4.1 tolerance test conditions specified in the "sample should be completely surrounded by air (with the exception of the necessary supporting points), and test the temperature of the measuring system and surrounded by specimen everywhere temperature gradient (near the sample measured) should be within plus or minus 2 ℃ test temperature and no more than 1 ℃ or the total maximum of 2.2 ℃ per meter (specimens not work)".

In MIL-STD-202F, 2.2.1 and MIL-STD-883C, 4.5.8, permissible temperature change for environmental test chamber:

(1) Temperature change in the working area: The temperature change at any reference point and in the working area is kept within ±2℃ (i.e., the temperature fluctuation at any point).

(2) Spatial temperature change in the working area: The temperature at any point in the working area deviates from the base point no more than ±3 ° C within a given time (i.e., tolerance)

In IEC publication No. 68 and GB 2423, the performance index is defined as "tolerance". For tolerance size, it is defined as ±2℃ for high temperature test chamber and ±3℃ for low temperature test chamber.

B. Temperature performance index in product technical conditions

(1) Technical conditions of foreign products

There is a temperature difference and temperature by the ASTM, D2436 volatility, difference in temperature of the test method is: decorate nine thermocouples which began after testing the stability of temperature in the cabinet, once every 5 minutes surveying, measuring total of five times to get 45 data, calculating the average 45 data as box temperature, from 45 number selected two maximum and minimum value minus the respective box temperature, and then choose two from four difference maximum and the average, this value is the difference in temperature.

IEC publication No. 216, Part IV, Also provides temperature difference and fluctuation indexes in aging ovens. The test method of temperature difference is the same as THAT of ASTM. D2436.

BS 3898, temperature indicators for temperature uniformity and temperature fluctuation degree, its temperature uniformity test method is: when the temperature stability, decorate with the chamber of thermocouple testing two consecutive hours, each test point are calculated respectively and the center point of the average temperature difference, the largest is the temperature uniformity, and the plus sign means.

In the product samples of foreign companies, there are only two temperature indexes, namely tem. constancy and unifortmty, or tem. Variation and temperature error, which are not found in the product samples of foreign manufacturers.

(2) Technical conditions of domestic environmental test equipment products

There are three indexes of temperature fluctuation, temperature uniformity and temperature error stipulated in the technical conditions of products in China, such as low temperature test chamber, high and low temperature test chamber and wet and hot test chamber.The temperature fluctuation degree is the time error of the temperature at any point in the box, and the temperature error is the error value between the temperature at each point in the box and the nominal temperature, that is, the space error.National standard on the temperature fluctuation and the temperature error in the sense of understanding and testing methods are basically the same, but the technical conditions of temperature uniformity in the test and data processing and foreign different, our country rules using 30 minutes closed to each test point data, 15 respectively calculate the difference between the highest and lowest temperature in each data, then calculate the average difference of 15 times as evenness, apparently because not compared with nominal center of temperature or temperature, so temperature evenness index sign.

Due to the above technical requirements, three temperature performance indexes are used in the product samples and specifications by domestic manufacturers.

At present, the National Center for Quality Supervision of Environmental testing equipment only measures the temperature error and unexpected temperature uniformity when verifying environmental testing equipment in accordance with GB 5170 "Verification Method for Basic Parameters of Environmental testing Equipment for Electrical and Electronic Products".

6. Testing of the temperature performance index of environmental testing equipment at home and abroad

A working space is defined in the IEC general: "requirements as prescribed in the working space is to maintain a specified tolerance range of test chamber of that part of the" foreign manufacturers such as Japanese companies regulation 1/6 working space in the box wall side except outside the area, that is to say, meet the technical index of space only 30% of the trunk space.The product standard of China stipulates that the working space shall be 51% of the chamber space except the area 1/10 of the length from the box wall.It can be seen that the working space of our equipment is much larger and more products can be tested.

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