Complete Guide to Environmental Test Chambers / Temperature Humidity Chambers

Every product manufactured by industry is subject to environmental damage. Environmental testing can help you find problems in your products. In order to check the usability of your products, environmental test chambers accelerate environmental changes or increase the number of situations where the natural environment cannot be reached. So with the help of an environmental test chamber you can get information on how long your product can be used in a natural environment and find out how high your product can peak in extreme environments.

1 What is an environmental test chamber?

An environmental test chamber is used to test whether the sample to be tested is intact and functioning properly under the specified conditions. The environmental test chamber consists of two parts: the environment and the test chamber. The environment refers to various environmental conditions, the sum of external conditions that the sample to be tested is subjected to at a given time, which can be mechanical, climatic, biological, and various other environments. A test chamber is an enclosed space capable of achieving the specified test conditions and is used to simulate different test environments.

One of the very important test items is the climate chamber test, such as high temperature, low temperature, high humidity, low humidity, light, and even alternating heat and humidity cycle test links. Therefore, the environmental test chamber is also known as artificial climate chamber, environmental test chamber, constant temperature and humidity test chamber, high temperature and high humidity chamber, high and low temperature alternating chamber, etc. The main areas involved are electronic component reliability testing, chemical and new energy material stability investigation, automotive and parts design and manufacturing, semiconductor wafer production and packaging, drug (chemical, traditional Chinese medicine and biopharmaceutical) related stability research, cosmetics and food microbiological testing, and third-party testing.

If a product has quality problems, this is most likely due to external factors, such as different use environments and scenarios such as temperature, humidity and vibration, which were not anticipated or taken into account during design. For example, warm to cool climates, different corrosion effects, and many other factors.

In addition to the conditions of use, the various stresses to which the product may be subjected during packaging, transport and storage operations, which may cause damage or shorten the product’s service life, are also taken into account.

2 Types of environmental test chambers

When an item is placed outdoors, it is likely to be subjected to natural environments such as wind, sun, altitude, humidity, cold, shock, salt spray, sand and dust. For different natural environments there are different testing standards and different types of environmental test chambers.

Common environmental tests mainly include: low-pressure test, high-temperature test, low-temperature test, thermal shock test, solar radiation (sunshine) test, rain test, moisture test, mould test, sand and dust test, water immersion test, freezing rain test, etc.

3 Working principle of environmental test chambers

The working principle of environmental test chambers can be interpreted mainly through two physical parameters, including temperature and humidity.

The environmental test chamber consists of two parts: temperature regulation (heating and cooling) and humidification. Through the rotating fan installed in the top of the chamber, the air is discharged into the chamber to achieve gas circulation and balance the temperature and humidity inside the chamber. The data collected by the temperature and humidity sensors built into the chamber is transmitted to the controller for editing and processing to regulate the temperature and humidity.

Temperature control

In order to control the temperature, the test chamber must be able to perform two functions: heating and cooling. In addition, it must be possible to regulate the temperature inside the chamber evenly.

Specific technology for the distribution of air within the environmental test chamber guarantees a high degree of uniformity of temperature throughout the chamber, ensuring that all components and surfaces are subjected to the same temperature.

The mechanical cooling system of the environmental test chamber consists of a closed circuit system with the following main components: compressor, condenser, expansion valve, evaporator.

Through the compression and subsequent expansion of the refrigerant gas, the environmental chamber will achieve uniform cooling throughout.

Environmental test chambers are usually classified according to two minimum temperature values: single stage with a minimum temperature of -40℃ and double stage (i.e. with a cascade system) with a minimum temperature of at least -70℃.

The mechanical heating system consists of electrically heated elements placed near the ventilation system, through which the heated air is transferred to the interior of the chamber. The two functions, cooling and heating, are controlled by a PLC according to the cycle parameters set by the operator to ensure the required performance.

Humidity control

In order to control humidity, the test chamber must be able to perform both humidification and dehumidification tasks, and must also be able to achieve a uniform distribution of humidity within the chamber.

Direct humidification is achieved by means of an electric humidifier, which ensures aerosol-free humidification by injecting steam through the airflow holes behind the air recirculation fan. The humidifier is controlled by a dedicated algorithm for increased reliability.

The test chamber is dehumidified by a mechanical system based on the condensation principle, using the same mechanical system as for cooling. According to this principle, when a cooler object is exposed to a warmer environment, the moisture in the air condenses on the surface of the cooler object. The evaporator is the lowest temperature element in the test chamber and will therefore be used with a dedicated section to reduce the humidity level in the chamber.

4 What tests are environmental test chambers used for?

We use different environmental test chambers for different purposes. For environmental testing, chambers are typically used for four main types of tests.

Steady-state testing

A test chamber that controls temperature, humidity or other factors within a certain range and maintains the temperature for a certain period of time. You can use this type of test to measure the service life of a product or to test stability over a long period of time in a specific environment. The results of this test will be more accurate.

It can simulate the adaptability of products under different environmental conditions such as high temperature and high humidity / high temperature and low humidity / high temperature / low temperature. It is widely used for testing products in electronics, electronics, food, automotive, rubber and plastic, metal, chemical and building materials.

Thermal cycling test

In this test, the test chamber provides your product with two extreme environments and switches between them over a period of time. This is a slow process. The changes in your product should be visible during the test.

Thermal shock test

This test is exactly what it sounds like – the test chamber quickly provides an extreme environment for your products. You will then find out the limits of their ability to combat extreme environments.

Salt spray test

Also known as the salt spray test, it is widely known as a type of corrosion test. Using this test, you can discover the usability of your products when exposed to a real environment.

Although the thermal cycling test and the thermal shock test are similar, they are not the same. The thermal cycling test is a slower process than the thermal shock test. Although both provide two environments for the product, the thermal cycling test is slower than the thermal shock test. The thermal cycling test will provide manufacturers with accurate results when controlling certain temperatures and humidity. The thermal shock test, on the other hand, will provide you with data on the durability of your product when switching between the two extreme environments.

Rapid temperature change test, is the product in the design strength limit, the use of temperature acceleration techniques to change the external environmental stress, so that the product in the thermal stress and should change, through the acceleration of stress to make the potential product defects emerge, for improving product shipping yield and reduce the number of rework has a significant effect. The products are widely used in aerospace, military, scientific research institutes, universities, quality control institutes, automotive parts, electronic and electrical, new energy, LED, mobile phones, plastics, displays, communications, chemical hardware and other industries.

5 How to read the parameters of environmental test chamber?

High and low temperature test chamber, for example, in the environmental test chamber pre-evaluation, and even the back-end production commissioning process, in addition to the temperature range mentioned at the beginning, we will also focus on the following key indicators.

Temperature change rate: simply put, every minute, the internal temperature rise / fall of the value of the chamber.

Temperature deviation: After the device has reached the set value and stabilised, the temperature value at each measuring point is recorded against the temperature value indicated by the device, once every minute, 30 times in total. The deviation of the maximum/minimum value from the set value during the process is the desired value.

Temperature fluctuation: again using the data collected during the temperature deviation process described above, the maximum value of the temperature difference between each collection point in the working space over a period of 30 min.

Temperature uniformity: again using the data above, the arithmetic mean of the maximum spatial temperature difference between the 9 test points at each minute over 30 minutes.

Q: With temperature uniformity, do I still need temperature fluctuation as an indicator?

Yes.

Although the temperature uniformity can be expressed in the box space temperature balance of good or poor, but due to the calculation are used in the method of multiple averages, so that the temperature fluctuations at each point of the factor basically removed.

However, for the test equipment temperature performance indicators only marked temperature uniformity is not enough, there must also be temperature fluctuation indicators, that is, the size of the temperature change at each point over time, in order to fully describe the changes in the temperature field in the box, especially when the temperature fluctuations are large.

Q: With temperature deviation, why do I need temperature uniformity and fluctuation?

Temperature test chamber fluctuation is a very important indicator

Constant temperature and humidity test chamber, high and low temperature alternating humidity and heat test chamber and other equipment is a special requirement for temperature fluctuations, so the need to mark the temperature fluctuations. Because when the temperature fluctuation of the humidity and heat chamber, will bring a larger humidity fluctuations, increase the humidity error, may exceed the humidity allowable deviation.

6 How do I choose a temperature and humidity chamber?

How do I choose the volume size?

When placing the test product (component, assembly, part or machine) into the climate chamber for testing, in order to ensure that the atmosphere around the test product can meet the environmental test conditions specified in the test specification, the volume of the working chamber of the climate chamber should be at least 3 to 5 times the volume of the outline of the test product.

What is the appropriate temperature range?

The higher the upper temperature limit, the greater the temperature difference between the inside and outside of the box, the less uniform the flow field inside the box and the smaller the available studio volume. On the other hand, the higher the upper limit temperature, the higher the heat resistance requirements for the insulation materials (e.g. glass wool, etc.) in the chamber wall sandwich. The higher the requirements for the sealing of the chamber, the higher the cost of making the chamber.

At present, the temperature test chamber range is generally -70℃ ~ +180℃. These temperature ranges can usually meet the needs of most military and civilian products temperature testing.

How much humidity range is appropriate?

Most of the humidity indicators given by the environmental test chamber is 20% ~ 98% RH or 30% ~ 98% RH, if the humidity and heat test chamber without dehumidification system, the humidity range of 60 ~ 98%, this type of test chamber can only do high humidity test, but its price is much lower.

The vast majority of the current temperature and humidity box are using the principle of refrigeration dehumidification, in the box of air pre-conditioning chamber plus a set of refrigeration light tube. When the wet air passes through the cold tube, its relative humidity will reach 100% RH, as the air is saturated with condensation on the light tube, making the air drier. This type of dehumidification can theoretically reach a dew point temperature below zero degrees, but when the surface temperature of the cold spot reaches 0°C, the water droplets condensing on the surface of the light tube will freeze, thus affecting the heat exchange on the surface of the light tube and reducing the dehumidification capacity. And because the box cannot be absolutely sealed, the wet air in the atmosphere will seep into the box and bring the dew point temperature back up. On the other hand, the wet air flowing between the light tube is only in contact with the light tube (cold spot) the instant it reaches saturation and precipitates water vapour, so this dehumidification method is difficult to make the dew point temperature in the box to 0 ℃ below. The actual zui low dew point temperature achieved is 5 to 7°C. Dew point temperature 5 ℃ is equivalent to the absolute moisture content of 0.0055g/Kg, corresponding to a relative humidity of 20% RH temperature of 30 ℃. If the required temperature of 20°C into the relative humidity of 20% RH, the dew point temperature at this time is -3°C, using the cooling method of dehumidification is very difficult, you must choose the air drying system to achieve.

Control methods

Temperature and humidity test chambers have constant test chambers and alternating test chambers in two cases. Ordinary high and low temperature test chamber generally refers to the constant high and low temperature test chamber, its control mode: set a target temperature, the test chamber has the ability to automatically thermostat to the target temperature point. Constant temperature and humidity test chamber control control method is similar, set a target temperature, humidity point, the test chamber has the ability to automatically thermostat to the target temperature, humidity point. High and low temperature alternating test chamber has the ability to set one or more high and low temperature changes, cycling procedures, the test chamber has the ability to complete the test process according to the preset curve, and can be within the range of the maximum temperature rise, cooling rate capability, precise control of temperature rise, cooling rate, that is, you can set the slope of the curve to control the rate of temperature rise, cooling. Similarly, the high and low temperature alternating heat and humidity test chamber also has the ability to preset the temperature and humidity curves, and control them according to the preset. Of course, the alternating test chamber have constant test chamber function, but the alternating test chamber manufacturing costs are higher, because the alternating test chamber need to be configured with automatic curve recording device, program control instrument, but also to solve the test chamber in the case of high indoor temperature to open the refrigeration machine and other issues, therefore, the price of alternating test chamber than the price of constant test chamber is generally higher than 20%. Therefore, we should be realistic to the needs of the test method as the starting point, the choice of constant test chamber or alternating test chamber.

Wind speed

The relevant standards provide for environmental testing, temperature and humidity chamber wind speed should be less than 1.7m / s, for the test itself, the smaller the wind speed the better, the wind speed will accelerate the test piece surface and air flow within the chamber heat exchange, the authenticity of the test is not conducive. But in order to ensure the uniformity of the test chamber, the test chamber has a circulation of wind is necessary. However, rapid temperature change test chamber and temperature, humidity, vibration and other multi-factor integrated environmental test chamber, in order to pursue the rate of temperature change, must accelerate the flow of circulating air within the chamber, the wind speed is usually 2 ~ 3m / s. Therefore, for different purposes, the wind speed limit is not the same.

Temperature fluctuations

Temperature fluctuation is a relatively easy parameter to achieve, and the actual temperature fluctuation of most test chambers produced by all environmental test equipment manufacturers can be controlled within a range of ±0.3°C.

Uniformity of temperature field

In order to more correctly simulate the actual environmental conditions suffered by the product in nature, the surrounding area of the product under test must be guaranteed to be under the same temperature environment conditions in the environmental test, for which the temperature gradient and temperature fluctuations within the test chamber must be limited. For example, in the general rules of the environmental test method for military equipment, it is clearly stipulated that “the temperature of the measurement system near the test sample shall be within ±2°C of the test temperature, and its temperature work shall not exceed 1°C/m or a total value of 2.2°C (the test sample does not work)”.

Accurate control of temperature

The majority of environmental test chambers in the measurement of humidity is the wet and dry bulb method, the relative humidity deviation should be ± 23% RH. To meet the requirements of humidity control accuracy, humidity test chamber temperature control accuracy is high, temperature fluctuations are generally less than ± 0.2 ℃. Otherwise it is difficult to achieve the requirements of humidity control accuracy.

Cooling method

If the test chamber with refrigeration system, the refrigeration system needs to be cooled. There are two forms of air-cooled and water-cooled test chambers.

7 What industry sectors are environmental test chambers suitable for?

Many industries test product prototypes to check reliability, characteristics, resistance to stress and other applications in the environment in which they are used. If the results of these tests are unsatisfactory, it is necessary to find the cause or defective components and to address the root cause and improve the product. Environmental test chambers are often used in the following industries to check the usability of products.

Aerospace

Environmental test chambers are used in the aerospace industry to simulate and reproduce typical environmental conditions during the landing, take-off and flight phases to ensure qualified, reliable and high standards of product performance and quality.

The automotive industry

Regulations in the automotive industry are constantly being updated and safety requirements are increasing. In addition to the basic issues of driver and passenger safety, there is also the issue of complying with emissions regulations in order to protect the environment.

Electronics industry

Environmental testing of electronic equipment is carried out to reduce the risk of product failure in the field. Testing is essential to ensure that products have a long service life and maintain their initial performance.

Battery industry

Environmental test chambers for battery testing are dedicated to lithium-ion battery testing. The purpose of the tests is not only to check the battery life, but also the degree of safety rating under specific environmental conditions.

Other areas

Environmental test chambers can also be used in the food industry, construction industry, energy industry, pharmaceutical industry, etc.

With the rapid development of modern industrial technology, electrical and electronic products are being widely used. At the same time, environmental conditions are becoming increasingly complex. Only by properly regulating the environmental protection measures of the products can they be protected from damage during storage and transport, and be safe and reliable during use.