Temperature and humidity test chambers include constant test chamber and alternating test chamber.The common high and low temperature test chamber generally refers to the constant high and low temperature test chamber. Its control mode is: set a target temperature
The inspection chamber has the ability to automatically stabilize the temperature to the target temperature point. The control mode of the constant temperature and humidity test chamber is also similar. Set a target temperature and humidity point. The test chamber has the ability to automatically stabilize the temperature to the target temperature and humidity point. The high and low temperature alternating test chamber has a program for setting one or more high and low temperature changes and cycles.
The test chamber has the ability to complete the test process according to the preset curve, and can accurately control the temperature rise and drop rate within the range of the maximum temperature rise and drop rate, that is, the temperature rise and drop rate can be controlled according to the slope of the set curve. Similarly, the high and low temperature alternating damp heat test chamber also has the ability to preset the temperature and humidity curves and control them according to the presets.
Of course, the alternating test chamber has the function of a constant test chamber, but the manufacturing cost of the alternating test chamber is relatively high. Because the alternating test chamber needs to be equipped with an automatic curve recording device and a program controller in the west, and the problem of starting the refrigerator when the temperature in the chamber is high must be solved. Therefore, the price of the alternating test chamber is generally more than 20% higher than that of the constant test chamber. Therefore, we should be realistic and take the needs of test methods as the starting point, and choose a constant test chamber or an alternating test chamber.
Temperature Change Rate
Ordinary high and low temperature test chambers have no index of cooling rate, and the time from ambient temperature to nominal minimum temperature is generally
90~120 min. The high and low temperature alternating test chamber and the high and low temperature alternating damp heat test chamber all have the requirements for temperature change speed, which generally requires 1 ℃/min, and the speed can be adjusted within this speed range. The temperature change rate of the rapid temperature change test chamber is fast. The rate of temperature rise and drop can reach 3 ℃/min~15 ℃/min, and the rate of temperature rise and rise can even reach more than 30 ℃/min in some temperature sections
The temperature range of fast temperature change test chambers of various specifications and speeds is generally the same, that is, – 60~+130 ℃, but the temperature range for assessing the cooling speed is different. According to different test requirements, some of the temperature ranges of fast temperature change test chambers are – 55~ +80 ℃, while others are 40~+80 ℃.
There are two ways to describe the temperature change rate of the rapid temperature change test chamber, one is the average temperature rise and fall speed in the whole process, and the other is the linear temperature rise and fall speed (actually the average speed every 5 min). The overall average speed refers to the ratio of the difference between the highest temperature and the lowest temperature and the time within the temperature range of the test chamber.
At present, the technical parameters of temperature change rate provided by foreign environmental test equipment manufacturers refer to the average rate of the whole process. Linear temperature rise and fall speed refers to the temperature change speed that can be guaranteed every 5 minutes. In fact, for the rapid temperature change test chamber, the most difficult and critical part to ensure the linear temperature rise and fall speed is the cooling rate that the test chamber can reach within the last 5 min of the cooling section.
From a certain point of view, the linear temperature rise and fall speed (average speed every 5 min) is more scientific. Therefore, it is better for the test equipment to have two parameters: the average temperature rise and fall speed in the whole process and the linear temperature rise and fall speed (average speed every 5min). Generally speaking, the linear temperature rise and fall speed (average speed every 5 min) is 1/2 of the overall average temperature rise and fall speed.
According to relevant standards, the wind speed in the temperature and humidity chamber shall be less than 1.7m/s during the environmental test. For the test itself, the smaller the wind speed, the better. If the wind speed is too high, it will accelerate the heat exchange between the surface of the test piece and the flow in the chamber, which is detrimental to the authenticity of the test. However, in order to ensure the uniformity in the chamber of the test chamber, it is necessary to have circulating air in the test chamber. However, for the rapid temperature change test chamber and the temperature, humidity, vibration and other multi factor comprehensive environmental test chamber, in order to pursue the temperature change rate, the flow rate of the circulating air in the chamber must be accelerated, and the wind speed is usually 2~3 m/s. Therefore, the wind speed limit is different for different purposes.
Temperature fluctuation is a relatively easy parameter to realize. Most test chambers produced by all environmental test equipment manufacturers are actuallyThe temperature fluctuation can be controlled within ± 0.3 ℃.
Uniformity of temperature field
In order to more accurately simulate the actual environmental conditions of products in the nature, it is necessary to ensure that the
The surroundings are in the same temperature environment.
Therefore, it is very important to set the test temperature gradient and temperature fluctuation that meet the standard.
The humidity in the environmental test chamber is mostly measured by the wet and dry bulb method. The manufacturing standard of environmental test equipment requires that the 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 ℃. Otherwise, it is difficult to meet the requirements of humidity control accuracy.
If the test chamber is equipped with a refrigeration system, the refrigeration system needs to be cooled. The test chamber has two types of air cooling and water cooling.