Views: 241 Author: Site Editor Publish Time: 2019-12-11 Origin: Site
How to choose temperature and humidity test chambers？
The selection of temperature and humidity test chamber needs many considerations to make a suitable decision. Next, we will introduce how to select the temperature and humidity test chamber. When purchasing cost-effective equipment, we should pay attention to the size of the equipment at first, and then observe whether the manufacturer has perfect after-sales service.
Qingsheng temperature and humidity test chamber series provide consumers with appropriate products and reliable services.
Select the appropriate temperature and humidity test chamber, we can refer to the following ten aspects in detail.
The following provisions shall be followed between the working dimension of the climate box and the outline dimension 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% to heating products in the test.
B) The ratio of the windward sectional area of the tested product to the total area of the chamber on the section shall not be greater than (35-50)% (35% is recommended).
C) The distance between the outline surface of the tested product and the wall of the test chamber shall be at least 100-150 mm (150 mm is recommended).
In fact, the above three provisions are interdependent and unified. The working chamber volume of the climate environment test chamber shall be at least 3-5 times of the outline volume of the tested product.
At present, the range of foreign temperature test chambers is generally - 73 ～ + 177 ℃, or - 70 ～ + 180 ℃. In general, most domestic manufacturers are - 80 ～＋ 130 ℃, - 60 ～＋ 130 ℃, or - 40 ～＋ 130 ℃, and also have high temperature to 150 ℃. These temperature ranges can generally meet the needs of most domestic military and civil products for temperature test. Unless there is a special need, such as the product installed near the engine and other heat sources, the upper temperature limit cannot be blindly increased.
The humidity index given by environmental test chamber at home and abroad is mostly 20-98% RH or 30-98% RH. If there is no dehumidification system, the humidity range should be 60-98%. This kind of test chamber can only do high humidity test, but its price is much lower.
There are two cases of temperature and humidity test chamber, constant test chamber and alternating test chamber.
The ordinary high and low temperature test chamber generally refers to the constant high and low temperature test chamber. The alternating test chamber has the function of constant test chamber. But the manufacturing cost of the alternating test chamber is higher, generally more than 20% higher than the price of the constant test chamber.
Ordinary high and low temperature test chamber has no index of cooling speed, and the time from ambient temperature to nominal minimum temperature is generally 90-120min. High and low temperature alternating test chamber and high and low temperature alternating humidity and heat test chamber have the requirements of variable temperature speed, which generally requires 1 ℃ / min. The speed can be adjusted within this speed range.
The rapid temperature change test chamber has a fast rate of temperature change. The rate of temperature rise and temperature drop can reach 3 ℃ / min ~ 15 ℃ / min, sometimes even more than 30 ℃ / min in some temperature sections. There are two expressions about the temperature change rate of the rapid temperature change test chamber. One is the average temperature rise and fall speed in the whole process, the other is the linear temperature rise and fall speed (actually the average speed every 5 minutes). From a certain point of view, the linear temperature rise and fall speed (average speed every 5 minutes) is more scientific.
According to the relevant standards, the wind speed in the environmental test chamber shall be less than 1.7m/s during the environmental test. For the test itself, the smaller the wind speed is, the better the accuracy of the test data will be higher. If the wind speed is too quick, it will accelerate the heat exchange between the surface of the test piece and the flow air inside the chamber, which is not conducive to the authenticity of the test. However, in order to ensure the uniformity of the chamber, it is necessary to have circulating air in the chamber. However, in order to pursue the rate of temperature change, it is necessary to speed up the velocity of circulating air in the rapid temperature change test chamber, which usually is about 2-3m / s.
Temperature fluctuation is a relatively easy parameter. The actual temperature fluctuation of most test chambers produced by all environmental test equipment manufacturers can be controlled within the range of ± 0.3 ℃.
In order to more accurately simulate the actual environmental conditions of products in nature, it is necessary to ensure that the surrounding of the tested products are in the same temperature environment in the environmental test. Therefore, the temperature gradient and temperature fluctuation in the environmental test chamber must be limited.
Most of the humidity in the environmental test chamber is measured by the wet and dry bulb method. According to the requirements of GB10586, the relative humidity deviation shall be ± 23% RH. In order to meet the requirements of humidity control accuracy, the temperature control accuracy of humidity test chamber is high, and the temperature fluctuation is generally less than ± 0.2 ℃.
If the test chamber is equipped with a refrigeration system, the refrigeration system needs to turn to cold at first. There are two types of test chamber, air cooling and water cooling.