Considerations In Choosing An Environmental Chamber

What Is An Environmental Chamber?

An environmental chamber is used to test various types of equipment under controlled environmental conditions. These conditions include temperature, the most common variable, and sometimes, humidity. More advanced types can run programs to cycle the variables over extensive ranges and are used to validate the performance of various types of equipment when subjected to extremes of temperature, and humidity. Also needing to be considered is the number and type of connections available for connecting to the unit under test. Power, temperature probes, thermocouples, and communication busses are passed through ports that can be on either side, both sides, and even the front door. Some specialized types of chambers are used for EMI testing and will not be covered here.

Sizes

Chambers can range in size from small sub-cubic foot to chambers you can walk into. Portable chambers are not this big, but can be large enough to hold several rack size pieces of equipment.

Temperature Ranges

Temperature ranges are determined by:                         

• Amount of power available
• Size of the chamber
• The amount of cooling needed
• The amount of heating expected from the article under test
• The number of test articles run simultaneously

Measurement units can be in either Celsius or Fahrenheit, and BTUs (British Thermal Units) are used to quantify the amount of heat that can be moved. Cooling can be provided in many ways depending on how fast or how cold the chamber needs to be. All chambers will need some level of cooling if only to maintain ambient, or a fixed rise above ambient temperature with a test article powered up inside. The lowest temperature a chamber can achieve is determined by how many compressors, or stages, it has. Single stage chambers can cool to roughly -35° C. Two stage units will achieve roughly -70° C. If you need fast cooling many chambers incorporate a liquid nitrogen fitting. Known as LN2 chambers, these can shorten temperature cycle times and, by accelerating temperature excursions, expose problems much faster. This is also due to physical stresses that are caused by rapid contraction and expansion over temperature as opposed to slower temperature transitions. Mechanical refrigeration is much slower as well as being much noisier.

Humidity

The ability of equipment to withstand harsh humid climates can be evaluated using chambers that incorporate humidity control. As with other chambers a drain for condensation is especially important to have. An additional requirement for humidity chambers is a supply of soft water. This is so that the chamber does not develop scale from hard water. Depending on the size of the chamber and the temperature swing, together with the ambient humidity, a significant amount of condensation can develop. There are two types of humidity conditions, condensing, and non-condensing. Which you use will depend on what kind of equipment test you are testing. Marine equipment will have a different requirement than laboratory equipment.

Common Sense Cautions

As with anything that produces extremes of temperature, caution must be exercised when handling test articles at the conclusion of an extreme temperature test. Remember that sub zero temperatures can cause burns as well as frostbite. It is best, unless the test protocol requires otherwise, to return the test article to the ambient temperature while it is still in the chamber.

Where To Find Environmental Chambers

Since 2005, Axiom Test Equipment has been providing a variety of environmental chambers for rent or sale. Additionally, we offer repair on most brands and types of environmental chambers. Major manufacturers we carry include Espec, Temptronic, Test Equity, Tenney, Thermonics, and Thermotron. Axiom Test Equipment offers a wide range of environmental chambers for your needs, with temperature capabilities ranging from -90°C to over 200°C and inner dimensions that work for bench top up to many cubic feet.

To learn more about any of these instruments, or to rent or purchase these or other test equipment, please visit Axiom Test Equipment’s website at www.axiomtest.com to view our inventory. If you would like help selecting the right equipment for your project, contact Axiom Test Equipment’s sales department at sales@axiomtest.com, or call an Axiom sales representative at 760-806-6600.