Temperature Test Chambers | Differences between constant and alternating humidity?

Damp heat tests simulate the effects of hot and humid environments on products in actual use on the one hand, and accelerate the ability of components and materials to withstand the effects of moisture deterioration under typical high temperature and high humidity conditions on the other. There are two types of heat and humidity tests: constant heat and humidity and alternating heat and humidity. Both tests rely on a temperature and humidity test chamber.

Test Definition and Criteria

Constant damp heat is mainly used to determine the adaptability of electrical and electronic products for use, storage and transportation under high humidity conditions; alternating damp heat is mainly used to determine the adaptability of electrical and electronic products for use, transportation and storage under a combination of high humidity and cyclic changes in temperature.

Corrosion process

Constant Hygrothermal: High temperature and high humidity acting on the sample can constitute water vapor adsorption, absorption and diffusion. Many materials in the moisture absorption expansion, performance deterioration, causing material strength reduction and other major mechanical properties of the change, adsorption of water vapor insulation materials will cause a decline in electrical properties.

Alternating humidity and heat: In high humidity conditions, the use of temperature cycling caused by condensation and drying of the alternating process, so that the water vapor into the internal samples of the “respiratory” effect, thus accelerating the corrosion process.

Commonly used test standards

Constant humidity and heat: GB/T 2423.3, IEC 60068-2-78;

Alternating humidity and heat: GB/T 2423.4, IEC 60068-2-30.

Temak temperature and humidity test chamber

Test method

According to the actual situation, determine whether the test sample should be pre-treated;

Place the sample in the constant temperature and humidity box, adjust the distance between the sample and the wall of the test box, the test box should be maintained as a standard atmospheric environment (25 ℃ room temperature, 50% R.H);

Increase the temperature to the specified severity level at a rate of not more than 1°C/min and allow the sample to stabilize. Keep the humidity at constant (50% R.H.) during this period to avoid condensation of the sample; then adjust the humidity in the chamber to the specified test severity level within 2h;

After the temperature and humidity in the chamber reach the specified value and stabilize, start to calculate the duration of the test and keep it under the high temperature and high humidity environment for the specified time;

Recovery after test: the humidity shall be reduced to normal humidity within 0.5h, and then the temperature shall be restored to normal temperature within 0.5h.