What is an environmental test chamber?

An environmental test chamber is a system that allows a user to control the environmental conditions of an enclosed space to run controlled tests on a subject. Environmental test chambers can run in size from half a cubic foot all the way up to 12,000 cubic foot drive in rooms. There are also multiple environmental conditions that test chambers can recreate: temperature and humidity conditions, temperature only conditions, and corrosive conditions through the use of salt spray.

How does a test Chamber Work?

To create temperature and temperature humidity conditions, environmental test chambers use electric heaters to create temperature and refrigeration systems to cool or remove temperature from the environment. The refrigeration systems can be either mechanical or a liquid cooling based system with pros and cons for each. To introduce humidity to the system, steam generators are used and to remove humidity a mechanical dehumidifying system is used. To boost the humidity range of the test chamber an air dryer can be added to allow the test chamber to reach a lower relative humidity. Learn more about AES’ wide line of temperature and humidity test chambers here. To create the salt spray, a salt solution is prepared and stored in the tank then compressed air is used to force it through a nozzle and create a mist in the test chamber. The MX Series chamber is a unique style of salt spray chamber with its clear walls allowing total product visibility during testing.

Diving in further, there are multiple types of temperature testing and different test chambers built for those types of testing. Steady state testing means the test chamber holds the environment at a certain temperature (and humidity if necessary) for a long period of time. Test chambers built for this kind of testing have a high temperature control to ensure that the test is as accurate as possible. The LH Series is a good example of a chamber with this kind of testing capacity. Thermal cycling testing has the test chamber cycling from a selected temperature to another with a focus on the ramp rate that it takes to reach those temperature levels. At AES we have two styles of chambers for thermal cycling that will fit almost any lab space: the FD/HD Series is our floor standing line and the SD/BHD Series is our benchtop line. Finally, there is thermal shock testing. This style of testing is when a product is quickly exposed to drastically different temperatures. At AES we use a two zone test chamber in our SM Series to achieve this with one cool zone and one heated zone and the product is then transferred between the two zones via a pneumatic elevator. By rapidly exposing your product to two drastically different temperatures you can test to find product failures and as well as testing your products ability to cope with the different climatic zones.

Thermal Cycling vs Thermal Shock

There are two types of temperature testing that while similar in name, are very different in their actual procedures. Both thermal cycling and thermal shock testing require bringing a product to two different temperature extremes but where they deviate is the time it takes to reach those extremes.

Thermal cycling is a slower process where the product is brought to the two temperature extremes over a period of time. The biggest factors in testing like this is the ramp rates of the test chamber to the two temperature extremes. Depending on how you want to test your product, you can vary the ramp rates to meet the level of stress you want to put on the product. The ramp rate is very important to the test since it is what applies the level of stress to the test chamber. Also thermal cycling has long soak periods where the product is left at a certain temperature level to “soak” in that thermal condition.

Where thermal cycling is a slower process, thermal shock testing is much quicker in terms of introducing the product to the other temperature. In a multiple compartment thermal shock test chamber, the chamber has two (or three) zones. One zone is the upper temperature limit and the other zone is the lower temperature limit, the third zone can be added for ambient temperature exposure. A basket is then used to quickly and autonomously transfer the product being tested between the zones. This allows for the product to be taken from extreme and immediately be exposed to other extreme, hence the name “thermal shock testing.” The biggest factor in this type of testing is recovery time. Recovery time applies to two areas in testing depending on what standard is being tested for. It can either apply to the product or the air. When it is air recovery it means that the air of the temperature has to recover to set temperature when the product is introduced. Product recovery means that the product has to reach the set temperature in a certain amount of time after it was introduced to the zone.

Are there standards for these types of testing?

Depending on what you are testing there are multiple standards that apply to each type of testing. There are JEDEC standards that apply for thermal cycling of microelectronics as well as ASTM standards for cycling photovoltaic modules. For thermal shock testing, there are military standards for product testing for products entering the defense industry.

Salt Spray Testing

Salt spray environmental test chambers are used to test the corrosive properties of products. Salt Spray test chambers are primarily used to test how well finishes, paints, and other products can last when exposed to a real world situation. By using a salt spray environmental test chamber, our customers can see years of corrosive exposure in a much shorter period of time.

Our salt spray test chambers hold the internal testing environment at a constant 95ºF and the salt and the spray is generated by using compressed air to create a pressure differential in the nozzle. This pressure differential sucks salt solution into the nozzle and as it passes through the nozzle, the spray that saturates the interior of the test chamber is created.

There are many standards that apply to salt spray testing and salt spray test chambers. The two major organization that have standards for salt spray testing are American Society for Testing and Materials (ASTM) and the United States Department of Defense (MIL-STD). By creating test standards, it allows for products entering those markets to be held to the same level of quality and end users know what level of scrutiny their product has passed through. Especially for products going to the Department of Defense, it allows the military to know how much field stress they can put on products without them failing.

Two of the more common standards for salt spray testing are ASTM-B117 and ISO 9227. Both specifications layout the apparatus, procedure, and conditions required to create and maintain the salt spray test environment. ISO 9227 applies specifically metals, alloys, and coatings, whereas ASTM-B117 does not have specific test specimen and is a broad spectrum standard.

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