Temperature Test Chamber Testing Standard | I

With the advancement of modern technology, temperature test chamber has become an important and indispensable equipment for product reliability assessment. This article discusses the standard process of temperature and humidity testing.

I. Pre-test Preparation

Temperature and humidity test is never simply put the sample into the temperature test chamber so simple. Scientific testing has begun from the preparation stage.

temperature test chamber

We need to ensure that:

1. Calibration of temperature test chamber

Usually by the professional metrology department once a year for external calibration, the main test before the calibration certificate to check whether the validity period, to confirm that the equipment is in a usable state.

2. Stability of the test environment

Equipment placement selection of well-ventilated, away from heat sources and direct sunlight in the test area.

3. Sample pre-treatment

According to the characteristics of different products, the necessary cleaning and pre-treatment of samples.

Sample pre-treatment key requirements:

1. Geometric parameters

Cross-sectional area: Keep uniform and regular;

Total volume: meet the space requirements of the temperature test chamber;

Minimum spacing: keep at least 10cm from the equipment wall.

2. Physical Characteristics

Density: uniformly distributed;

Weight: not exceeding the equipment load limit;

Material: consistent thermal conductivity.

3. Placement principle

Do not cover the temperature and humidity sensors;

Avoid covering each other between samples;

Ensure smooth air convection.

4. Quantity control

According to the effective testing space of the temperature test chamber;

Ensure that each sample is fully exposed.

II. Sample Load

The total mass of the load does not exceed 80 kg per cubic meter of workspace volume;

The total volume of the load is not greater than one-fifth of the workspace volume;

In any cross-section perpendicular to the dominant wind direction, the sum of the load area should not be greater than one-third of the cross-sectional area of the workspace, the load is placed so as not to block the flow of airflow.

The specific selection of the test load can also be negotiated between the two sides, or according to the provisions of the relevant standards.

III. Temperature and humidity test items

Temperature and humidity test mainly includes the following typical methods and common test parameters:

1. Temperature gradient test

This process through a specific rate, gradually raise or lower the temperature and store the same time period at the set temperature, through the instrumentation to monitor the electrical properties of the product under test in different temperature conditions or other forms of change. Each step on the temperature gradient is used to calibrate the sample to work in accordance with the design requirements, therefore, whether the temperature gradient can be executed accurately and without error, is for the control ability of the temperature test chamber and the output of hot and cold energy control ability to put forward high requirements.

2. Temperature cycling test

Temperature cycle test simulates the adaptability of the product in the process of changing temperature. Temperature and humidity test chamber will maintain a specific rate of temperature rise and fall, through repeated uniform temperature changes, so that the test samples inside and outside the loading and unloading stress is fully released, while testing the product's thermal deformation fatigue as well as testing the stability of materials.

3. Damp heat test

Damp heat test can be divided into constant damp heat test, alternating damp heat test, temperature and humidity combination cycle test.

1. Constant damp heat test

Constant temperature and humidity test requires the temperature test chamber at the same time to control the temperature and humidity, with a fixed temperature and humidity conditions to the sample to impose a balanced stress, the core of this experiment is a stable test conditions and a long period of time, the assessment is the diffusion of moisture and infiltration, from the point of view of the “quantitative to qualitative change” to verify the reliability of the product. The test conditions are often carried out under 40-95% relative humidity and temperature range of 20-85℃. This test can simulate tropical, subtropical and other humid environments to test the moisture resistance and corrosion resistance of products. However, the test conditions are implemented according to various standards, and the temperature and humidity test standards will be different for different industries and products. For example, electronic components, medical equipment, aerospace and other areas of the test standards have their own characteristics. This test program does not allow interruption, otherwise it will lead to test failure.

2. Alternating temperature and humidity test

Alternating temperature and humidity test is based on the constant humidity and temperature, highlighting the temperature changes in the process of generating a large number of condensation on the mechanical and electrical properties of the product, focusing on the “breathing effect” under the influence of water penetration by strengthening the effect of the verification of the stability of the sample. This test has a much higher level of resistance to humidity and heat than the constant humidity and heat test.

3. Temperature and humidity combination cycle

Test temperature and humidity combination cycle is a very destructive test, in short, the sample is fully absorbed water, and then add a few times frozen, through the physical change of water into ice to further expand the sample gap, amplifying the “breathing effect”. Combined temperature and humidity cycling test is more severe: more temperature changes or “respiration” in a given period of time; a greater range of temperature cycling changes; a higher rate of temperature cycling changes; including multiple temperature changes below 0 ℃. Accelerated “breathing” and the freezing effect of moisture adsorbed in the crevices of the test specimen are the basic characteristics of the temperature and humidity cycling test.

It should be emphasized, however, that the icing effect only occurs if the gap is large enough for adhering moisture to penetrate, which is usually the case with metal component seals or lead end seals.

Note: Condensation on the surface of the sample should be avoided under constant temperature and humidity conditions and can be achieved by preheating small samples; the alternating temperature and humidity test is used to determine the suitability of components, equipment or other products for use, transportation and storage under conditions of high cyclic humidity and temperature combinations that normally produce condensation on the surface of the test specimen. If this test is used to verify the performance of a packaged sample during transportation and storage, the test shall be performed with the package. For small, lightweight samples, it may be difficult to produce condensation on the surface of the sample and the user should consider alternative tests; due to the nature of the temperature cycling test, it is recommended that this test method be limited to samples whose structure produces the “breathing” and freezing effects of the moist temperature test and whose thermal characteristics are compatible with those of this Z/AD test. The recommended test method is limited to component test specimens whose structure produces the “breathing” and freezing effects of the damp temperature test and whose thermal characteristics are compatible with the rate of temperature change of this Z/AD test. For solid test specimens with small cracks or porous materials, such as those encapsulated in plastics, where water vapor absorption or diffusion plays a dominant role, constant temperature and humidity test is preferred. Where the temperature and humidity test, the general cycle is relatively long, therefore, for the temperature test chamber, the stability must be reliable, otherwise the test interruption must start again. Temak temperature and humidity test chamber temperature range -70 ℃ ~ +150 ℃, relative humidity range 10% -98% (10 ℃ ~ 95 ℃). Temperature and humidity regulation performance is accurate, with high consistency, repeatability and stability. Collected data can be multi-channel output, the output form includes graphics and excel data table.

Reference to the test standards, the purchase of temperature test chambers should also consider what aspects of it, we explain in the next issue.

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Temperature Test Chamber Testing Standard | II

Standard process and practical skills for temperature and humidity testing

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