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Combined Environmental Testing – Altitude, Temperature & Humidity

Simulating real-world conditions is critical to understanding how products react in a variety of environments. Perhaps no more important conditions exist in which to proactively test products than aerospace and military defense applications. Typically, these products and components must function properly at various altitudes, temperatures, and humidity conditions. Coupled with mechanical or electromagnetic vibration, combined testing is essential to understanding the material resistance to the effects of changing temperature and humidity environments at varying altitudes

Why is Combined Environmental Testing Important?

While the individual conditions on their own can be replicated, the importance of combined temperature, altitude, and humidity testing is critical in aerospace, defense, and electronics manufacturing where products and components are functioning in extreme environments. Navigational components of commercial aircraft and guidance systems for defense articles are just a few examples of critical components required to operate functionally in diverse conditions. Combined climatic testing allows manufacturers to replicate these conditions within a controlled environment to test, validate, and diagnose for potential failures in advance of their utilization. 

Most manufacturers utilize combined methods of temperature chambers, altitude testing chambers, and humidity testing chambers for engineering development, operational testing, and qualification. Many requirements involve actively powered devices or parts in operation at altitude including aircraft, missiles, and aerospace components. By synergistically combining environmental conditions, combined climatic testing simulates the effects that are likely to occur over the majority of the deployment life of the test article.

What Environmental Conditions Can Be Created?

To verify products remain operational and durable against the full range of environmental conditions to which they might be exposed, concurrently simulating temperature and altitude or altitude and humidity can help identify potential failures that may not manifest in each condition tested separately. 

MIL-STD-810 G Test Method 520.3 specifically addresses the combined effects of temperature, altitude, humidity, and vibration on airborne electronic and electromechanical components to ensure their safety, integrity, and performance during ground and flight operations. Identifying the specific profile, procedure, and step within MIL-STD-810 G will assist your test chamber manufacturer in designing the equipment to best match your requirements. 

Most altitude test chambers possess the capability to achieve altitude up to 100,000 ft. with extended ranges in some cases to 200,000 ft. The temperature range is typically offered between -70°C and +180°C, with humidity between 10% and 95% RH. Mechanical refrigeration or the use of liquid nitrogen are used to create a wide temperature environment, while rotary vane vacuum pumps of varying sizes create the ‘vacuum’ associated with high altitude conditions. Atmospheric steam generators are typically used to introduce humidity into the system bound within a maximum dry bulb temperature generally not to exceed 85°C. 

Test profiles within military and aerospace standards require the following combined environment testing conditions. Altitude with temperature is produced by cycling 5°C per minute or steady-state temperature testing between site level and 65,000 ft. Temperature and humidity are cycled between 10% and 95% RH typically at site level only. 

What to Look for in a Test Chamber?

While many manufacturers claim to make altitude test chambers, not all are created equal. Consider the following construction factors when determining which altitude chamber manufacturer is best suited for your needs. 

The chamber liner should be constructed of a minimum 16 gauge heavy-duty stainless steel material ensuring robust strength and rustproof quality. Seams should be hermetically sealed to prevent moisture migration during low-temperature operations. Consider external or internal pressure membranes in your selection process. These should be constructed of heavy-duty reinforced welded steel plates to withstand atmospheric pressures induced during testing. 

Additionally, look for a minimum 8” foam glass insulation with a 0.25 k factor to ensure strong temperature uniformity and efficiency. Finally, your manufacturer should offer reliable parts and labor warranty with start-up and service in the field available at request. 

Russells Technical Products has developed a reputation as the industry leader in altitude test chambers, specifically those used for combined temperature, altitude, and humidity testing. There is a reason many of our units are still in operation over thirty years later. Contact us today to learn more about our altitude test chambers and which solution best meets your needs.