Repeatability of environmental conditions of constant temperature and humidity test chamber

A constant temperature and humidity test box can be used for multiple tests of the same type of product, and a batch of tested samples may also be tested in different environmental test boxes, in order to ensure that the same batch of samples are specified in the same test specification The comparability of the test results obtained under the constant temperature and humidity environment test conditions inevitably requires the repeatability of the environmental conditions provided by the environmental test equipment. That is to say, the stress level (such as thermal stress, vibration stress, electrical stress, etc.) applied by the environmental test equipment to the tested product is consistent with the requirements of the same test specification.

The repeatability of environmental conditions provided by environmental test equipment such as constant temperature and humidity test chambers is guaranteed by the national metrological verification department in accordance with the verification procedures formulated by the national technical supervision agency. To this end, users in the electronic and electrical industry must be required to purchase a constant temperature and humidity test chamber that can meet the requirements of various technical indicators and precision indicators in the verification regulations, and the use time should not exceed the time limit specified in the verification cycle. If the commonly used electric vibration table meets the technical indicators such as excitation force, frequency range, load capacity, etc., it must also meet the requirements of precision indicators such as lateral vibration ratio, table acceleration uniformity, harmonic distortion, etc. as specified in the verification regulations. And the use period after each verification is two years, and more than two years must be re-verified before it can be put into use.

Measurability and controllability of environmental condition parameters of constant temperature and humidity test chamber

Selection of constant temperature and humidity test chamber

1. Selection of volume

When placing the test sample product (electronic appliances, components, components, components or the whole machine) in a constant temperature and humidity climate environment test chamber for testing, in order to ensure that the atmosphere around the tested product can meet the environmental test conditions specified in the test specifications, The following points should be observed between the working dimensions of the constant temperature and humidity test chamber and the outer dimensions of the tested product:

a) The volume of the tested product (W × D × H) shall not exceed (20 ～ 35)% of the effective working space of the test chamber (20% is recommended). It is recommended to select no more than 10% for products that generate heat during the test.

b) The ratio of the windward area of ​​the tested product to the total area of ​​the working chamber of the test chamber on this section is not greater than (35-50)% (35% is recommended).

c) The distance between the outer surface of the tested product and the wall of the test chamber should be at least 100-150mm (150mm is recommended).

The above three points are actually interdependent and unified. Taking a cubic meter box as an example, the area ratio of 1: (0.35 ～ 0.5) is equivalent to the volume ratio of 1: (0.207 ～ 0.354). 100 to 150 mm from the wall of the box corresponds to a volume ratio of 1: (0.343 to 0.512).

The environmental conditions provided by any constant temperature and humidity test chamber and other environmental test equipment must be observable and controllable, not only to limit the environmental parameters to a certain tolerance range, but also to ensure the reproduction of the test conditions Requirements for repeatability and repeatability, and it is also necessary from the safety of product testing, in order to prevent the uncontrolled environmental conditions from causing damage to the tested product and bringing unnecessary losses. At present, various test specifications generally require that the accuracy of the parameter test should not be less than one-third of the error allowed by the test conditions.

As you in the electronic and electrical industry, if you have any doubts in the process of purchasing a constant temperature and humidity test box, please contact a professional manufacturer of constant temperature and humidity box in time, we will provide you with the most effective solution!

Hair Brush

Zhejiang Hisun Electrical Appliance Co.,Ltd , https://www.cn-hisun.com