Environmental Test Chambers

Environmental chambers evaluate product quality and reliability, and identify manufacturing flaws and weaknesses in those products before they are released to the general market. Common tests undertaken in environmental test chambers are extremes of temperature and sudden variations of temperature in temperature chambers and cryogenic chambers, the effects of humidity and moisture in humidity test chambers, and salt spray test chambers which record the degrading effects of salt water on objects for manufacturer analysis. Other types of chambers include: AGREE chambers, altitude chambers, thermal shock chambers and vacuum test chambers. Causal environmental conditions such as airborne and structural vibrations, shock, dust and sand, electromagnetic and UV radiation are further tests carried out in test chambers to evaluate a product's reaction to the elements. As the nature of the tests which environmental chambers perform is widely varied, the common sizes of the chambers are also as broad. Test chambers can range from simple, smaller benchtop test chambers which can be used to test a small component, to a variety of sizes of altitude chambers, to the larger, more complex walk-in test chambers, and even drive-in chambers for vehicles and aircraft.

The validity of environmental test results is important as it is these results that future product modifications and improvements are based upon. Therefore, design and construction of the environmental test chamber has to be carefully considered. As it is a process test, chambers typically have a means of viewing and monitoring the testing procedure either through a viewing hole, or through a video feed. In some cases, an environmental test chamber will have a reach-in capability in order for the testing engineer to handle the product or material being tested. The method of process control is another consideration to be undertaken as control panels can be either analog or digital, fed by a computer or the web etc. The consistency with which an environmental test is performed is crucial to the reliability of the results, therefore it is wise to refrain from including unnecessary man-made interference with the process to keep it as uniform as possible. Each element of the test and testing conditions has to be taken into consideration - such as already existing environment and climate, the potential addition of interior chamber lighting and thus extra heat, and the variations that already exist between products and materials. Strict control during the process will yield the most accurate and useful results from the tests.

Test chambers are designed with the capacity to replicate not only normal, but also extreme environmental conditions. Temperature chambers can typically reach temperatures above 1000 degrees Fahrenheit, and cryogenic chambers produce temperatures on the other end of the scale achieving lows of -200 degrees Fahrenheit, or even lower with the help of liquid nitrogen. In addition to temperature variations which can be further tested by thermal shock chambers, humidity and air moisture content can be replicated with humidity ranging from 10-100% in most humidity chambers. These are basic tests which are commonly carried out on most products. Altitude chambers simulate extremely high altitudes to test the effects of pressure and air change, and routinely 10-8 Torr levels are achieved in vacuum environmental chambers. Means must be implemented to record the data of the product response to these tests for analysis, verification and future development and adjustment planning. Therefore, there is a two areas of focus within a testing chamber - that of producing the controlled conditions for the testing of the object or product, and the accurate recording of the results of that testing.

Industries which use environmental testing include: automotive, engineering, construction, medical, pharmaceutical, food processing, packaging and consumer. Everyday products such as car parts, cigarettes, make-up, medicines and kitchen appliances undergo testing by manufacturers to ensure their durability and effectiveness in certain environmental conditions. An important reason for the process of environmental testing is that it finds flaws and weaknesses in product design and lifespan before it reaches the public market. These findings allow for production adjustments and result in a better quality product arriving on the market. Once a product is tested and approved in extreme circumstances, there will be lower warranty claim expenses from replacement and repair, and this saves manufacturer expenditure. Without testing products in a variety of environmental conditions, it is a high risk for a manufacturer to sell the products under warranty. Customers are increasingly demanding longer warranties on products and goods, and it is imperative that a manufacturer has tested the product that he or she is guaranteeing to avoid high reimbursement costs. Testing can take many hours and can be a costly procedure depending on the size and process undertaken, and yet it is a wise manufacturing choice to undergo environmental testing, especially in terms of long-term expenditure and future benefit.

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Environmental Test Chamber Types

• AGREE chambers can produce fast temperature changes of 41-104˜F (5-40°C) per minute, even with large loads. Vibration test systems can be integrated within agree chambers, as they have removable floors.
  
• Altitude chambers test the effects of low pressure on an object and are capable of replicating low-pressure environments found at altitudes of up to 200,000 feet above sea level.
  
• Bench top test chambers reduce test time when testing small items.
• Cryogenic chambers replicate extremely low temperatures from -238 degrees F to absolute zero.
• Drive-in chambers accommodate large items, such as vehicles, and are useful when performing batch testing.
  
• Engineering Stress Screening (ESS) chambers change the temperature of a product at a highly accelerated rate through high air velocity conditioning.
  
• Environmental chambers replicate environmental conditions for engineering tests.
• High Altitude Simulation (HAS) chambers replicate environmental extremes that an airplane typically endures when in operation.
  
• Humidity Chambers are able to simulate a variety of humidity conditions in order to test the effects of humidity on an object. Used for specific testing in industrial and biotechnology applications.
  
• Mixed Flowing Gas (MFG) chambers are used to expose electronic equipment to a mixture of pollutant gases in an environment in which the temperature and humidity are controlled.
  
• Reach-in chambers often contain shelves and other amenities for easy storage and user convenience.
  
• Salt spray or fog chambers test the corrosion resistance of an object. The object usually hangs from a rod while the chamber introduces a salty residue, which creates a foggy atmosphere, although the object remains visible throughout the process.
  
• Temperature chambers test the effects of temperature on an object. Temperature cycling is performed alone or in conjunction with other tests, such as altitude and vibration tests.
  
• Thermal cycling or stress screening chambers involve the subjection of an object to extreme changes in temperature within a single chamber in which the temperature alternates between cold and hot for a given number of cycles.
• Test Chambers are enclosures designed to provide controlled environments for tests and experiments.
• Thermal shock chambers initiate automatic changes between two compartments, in which one compartment contains an extremely cold environment and one compartment contains an extremely hot environment. The rapid transference of the object between these two compartments of extreme temperatures causes a shock to the object.
  
• Thermotron chambers are used for thermal and dynamic testing and have shock and vibration capacity.
  
• Vacuum chambers are chambers from which almost all matter, especially air, has been removed.
  
• Vibration chambers apply shock vibrations of varying frequencies to an object, including the bumping, shaking and bouncing of an object, and can be administered in conjunction with temperature and humidity testing. Vibration chambers have sensors that perceive and monitor the object's reaction to the vibration.
  
• Walk-in chambers vary in size and can usually accommodate one or more persons. Walk-in chambers are useful when testing large objects and performing batch testing.  

Environmental Test Chamber Terms

Absolute Humidity - The amount of water vapor, or moisture, in a unit of air.
 
Absolute Vibration - The measurement of an object's vibration in comparison to a fixed point in space.
 
Accelerated Life Testing - The subjection of a product to stress during the development phase in order to gauge the quality of the product. The stress applied to the product often exceeds that which the product would sustain during normal use.
 
Accelerated Stress Testing - The subjection of a product to stress after production in order to identify production flaws before the product reaches retailers and consumers.  
 
Aggravated Testing - The process of applying greater stress to an object than that which the object would sustain during normal use, the purpose of which is to identify guidelines by which the product may be used.
 
Air-To-Air Thermal Shock - Also called "two-zone thermal shock," this process is the transferring of a product from a hot chamber to a cold chamber or other sudden changes of the air temperature.
 
Ambient Environment - The given temperature and humidity content of an indoor (internal) or outdoor (external) environment.
 
Atmospheric Pressure - The amount of force the atmosphere exerts upon the earth's surface, measuring 14.7 psi at sea level.
 
Batch Testing - A test procedure in which multiple items are tested at the same time.
 
Burn-In - The hastening of a product's aging process through the continuous operation of the product, usually at higher than moderate temperatures, in order to evaluate product quality.
 
Calibration - The process of comparison between the current operation of an object or a system and the operating standards of that object or system. Calibration determines the efficiency of an object and identifies errors and the manner in which the system can improve.
 
Corrosion - The gradual deterioration of a metal caused by oxidation or chemical reaction.
 
Critical Frequency - The frequency level at which point the destruction of the object subjected to such frequency begins.
 
Damping - Decrease in the vibration of an object.
 
Dew Point - The temperature of a given unit of saturated (containing the maximum amount of water vapor) air.
 
Dry Room - An environmental chamber in which the humidity level remains below a 14° F/-10° C dew point.
 
Environment - The internal and external conditions, regardless of the source, which affect a given object. The environment includes temperature, humidity, electricity, precipitation, etc.
 
Environmental Stress Screening - The determination of the working efficiency of an object or system through the identification of the effects of thermal changes upon the object or system.
 
Frequency - The rate of movement, measured in cycles, of a wave within a set time frame, usually one second. Frequency is often measured in hertz (Hz), which equals one wave cycle per second.
 
Highly Accelerated Life Test (HALT) - A test that assesses the lifetime of a product, reduces its development cycle time and increases confidence in the life-cycle reliability of the product.
 
Highly Accelerated Stress Test (HAST) - Product reliability test in which an object is subjected to high temperature, humidity and pressure. HAST has also come to be called Autoclave or Pressure Cooker Test (PCT).
 
Hermetic - The airtight sealing of an object.
 
Life Cycle Testing - The subjection of a product to stress comparable to that which the product will sustain during use in order to determine product quality.
 
Liquid-To-Liquid Thermal Shock - Alternately immersing an object in hot and cold liquids.
 
Product Recovery Time - The recovery time of a physical product after it has been subjected to testing. Product recovery time is dependent upon the location of the sensor in the load.
 
Psi (Pounds Per Square Inch) - Unit that measures the amount of pressure applied to an object.
 
Relative Humidity - The ratio of the current amount of water vapor in a given unit of air at a given temperature to the greatest amount of water vapor the unit of air could hold at that temperature.
 
Relative Vibration - The measurement of an object's vibration in comparison to a fixed point on the object.
 
Saturation Humidity - The maximum amount of water vapor a given unit of air can hold at a given temperature. Air becomes saturated when relative humidity reaches 100%.
 
Stress - Condition or force applied to an object that may impair the object's quality and performance.
 
Temperature/Humidity/Bias (THB) Test - Product reliability test in which an object is subjected to high humidity under a constant temperature. Test time greatly exceeds that of HAST test time.
 
Thermal Cycling - Subjecting an object to extreme changes in temperature within a single environmental chamber.

Thermal Shock - Stress sustained by an object as a result of rapid temperature changes.
 
Three-zone Thermal Shock - Moving the object from a hot to a cold chamber and vice versa, with an intermediate step of exposure to room temperature.
 
Transfer Time - The amount of time it takes for an object to be moved from one chamber to another.
 
Upstream Recovery Time - Also called "downstream recovery time," this is the time required for the air temperature to recover in the new zone. Upstream recovery time can be measured in the air stream prior to or following the test load.
 
Vibration - Motion of an object around a position of equilibrium.