This article contains information about altitude chambers and their use.
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An altitude chamber is a test chamber that is designed to simulate the altitude, vacuum, and temperature of environmental conditions at heights that match the flight patterns of all forms of aircraft, from commercial to military. The purpose of altitude test chambers is to test components and parts used in aircraft and the endurance and resilience of parts when they are shipped using airborne shipping methods.
Unlike hypobaric test chambers that test the effects of terrestrial altitude conditions, altitude test chambers combine multiple factors with altitude including temperature, humidity, icing, and, at times, vibrations. By taking all of the possible factors related to high altitude environments and combining them, it is possible to simulate and create real world high altitude conditions.
There tends to be confusion regarding altitude test chambers and hypobaric test chambers. Though they are designed to test the effects of altitude, their purpose is quite different. People unfamiliar with the test chamber industry believe that chambers used to enhance athletic performance and the effects of terrestrial high altitudes are the same as altitude test chambers. In many instances, the terms are used interchangeably.
Industrial altitude test chambers create far more extreme environments than those used to train and test people. The reason for this differentiation is the need to create conditions that examine the strength, durability, resilience, and capabilities of parts, components, and instruments used for aircraft and the shipment of delicate and sensitive tools.
To simulate the specific conditions at high altitudes of several thousand feet, specialized equipment is needed to produce the kind and quality of air found in such environments. A variety of vacuum pumps of different sizes are used for creating atmospheric conditions of 100,000 feet, which can be extended to 200,000 feet.
There are a variety of factors that have to be examined at high altitudes, such as a drastic loss in cabin pressure. Altitude chambers can simulate the loss by decompressing at a rate of close to 15 seconds or less.
Though the basic design of altitude test chambers is to recreate conditions high above the earth, they can also mimic the types of pressure found below sea level.
Each of these factors, high altitude, rapid decompression, and being below sea level, can be simulated through the adjustment of programmed controls and instrumentation, which can instantly produce situations that meet the testing parameters. These highly technical and complex devices save lives, improve products, and produce data that ensures protection for personnel and products.
Although altitude test chambers are referred to as altitude test chambers, the function of an altitude test chamber encompasses the creation of all of the possibilities that are found at extreme heights. One essential part is matching the temperature, which requires the use of single stage or cascade refrigeration.
The control of temperature in an altitude test chamber requires the ability to perform two functions, which are to create heat and cold. Regardless of the predetermined temperature, it has to be uniform throughout the space of the chamber. This particular function is an aspect of altitude test chambers that manufacturers take a great deal of pride in monitoring and creating.
In a single stage refrigeration system, the refrigerant is compressed once. During the process, the refrigerant is pulled into a cylinder and compressed with a single piston stroke. Additionally, a single stage system has one low side pressure or evaporator pressure and one high side pressure or condenser pressure. The benefit of a single stage refrigeration system is low cost and control over a limited range of temperatures.
A cascade system uses a refrigerant to condense a primary refrigerant that is operating at the proper level for the evaporator temperature. A high stage refrigeration circuit is used to cool a low stage circuit to achieve very low temperatures. This type of system has a low operating cost and is energy efficient. Its main benefit is its ability to achieve extremely low temperatures as low as – 120° C.
Additionally, cascade refrigeration systems are easy to maintain, making them ideal for use with high altitude test chambers. The wide range of temperatures along with the precision control system makes a cascade system the ideal choice for producing specific altitude conditions.
Added to the mix of tests performed by an altitude test chamber is humidity testing, which is done in conjunction with temperature and altitude testing. The addition of humidity to the other tests makes it possible to perfectly simulate actual real life conditions that a product may endure at high altitudes.
As with temperature and altitude, products can be severely damaged by humidity. The use of humidity tests helps determine the practicality and durability of coatings, paints, types of metals, and other materials. By properly diagnosing and measuring the effects of humidity, it is possible to extend and increase the lifespan of a product.
Vibration testing is designed to test a product‘s ability to withstand the effects of vibrations, which are common in aircraft. The test aims to simulate transportation conditions, flight control use, and control instrumentation while in flight, which are the types of conditions that a component will confront. The test applies vibrations to determine a part, component, or device‘s point of failure.
The data from the test provides formation regarding the limitations of a product and acts as a guide for improvements and further development.
Test chamber manufacturers take pride in the quality and performance of their altitude test chambers. Using expert designers and engineers, they carefully select the proper materials and instruments to ensure the precision and accurate performance of their products.
Altitude test chamber systems are highly complex with several subsystems, including the main chamber, pumping system, control system, and refrigeration system.
These complex and intricate systems require advanced technological expertise. Since the data acquired from test chambers is essential to the success of a product, the chambers are custom engineered to meet the specific conditions of a customer.
One of the main distinguishing features of altitude test chambers is their size, ranging from 5 cubic feet up to 65 cubic feet or larger. This aspect of an altitude test chamber is determined by the materials and components to be tested as well as how many components or materials will be tested at one time.
As with all types of industrial equipment, the facility where the test chamber will be used has to have sufficient area and space to store it. To provide the best possible performance, an altitude test chamber should smoothly fit into the operational space of the organization. Choosing the correct size ensures accurate test results and optimum performance.
As with all test chambers, the controls of an altitude test chamber are critical. Though there are simple controls for less sophisticated test chambers, altitude test chambers require an array of controls to monitor, set, and adjust the many functions that altitude test chambers can perform.
Since an altitude test chamber collects so much data, it is essential to have a controller that can provide instantaneous results while the chamber is in operation. Data is collected by dozens of sensors built into the chamber and has sufficient sensitivity to register all of the existing conditions and the reaction of the tested component to them.
As may be expected, in the technological age, computer interfaces are available for monitoring, activating, and assessing the activities of the chamber from a desktop or laptop computer. This added feature makes it possible to check data that is being collected from remote and off site locations.
When testing groups of products, it may be necessary to have shelves in the test chamber. They have to be configured to fit the needs of the product and the testing that is being completed.
The refrigeration unit provides the appropriate temperature for an altitude test chamber. The size of the refrigeration unit will vary depending on the size of the test chamber and the desired temperatures. An air cooled condenser may be necessary depending on the size of the compressor.
The interior and exterior of an altitude test chamber is made of steel with the interior being made of stainless steel that is tightly and securely welded. In order to maintain an air tight chamber, insulation is placed between the interior and exterior walls, which is normally 0.25 k factor fiberglass.
The exterior walls and frame are made of welded steel that has conveniently located access panels to enable servicing, maintenance, checking, and replacement of components. As with all the other aspects of the chamber, the interior and exterior of the doors are made of steel with exceptionally sturdy and smooth operating hinges.
Though there are standard colors for altitude test chambers, manufacturers make it possible for customers to choose the color they desire.
The image below offers a clear representation of the stainless steel interior of an altitude test chamber and its steel exterior walls.
The vacuum pump is an essential part of an altitude test chamber since it is required to bring the chamber down to the set vacuum level. The pump connects directly to the chamber and pumps through large ports. Vacuum pumps pump at speeds of hundreds of cubic feet per minute.
Interior lighting is designed to illuminate the workspace when the chamber is closed and in operation and when the door is opened. Proper lighting is necessary for users to see the objects being tested and for their safety. Generally, incandescent lighting is used.
A thermal alarm is included in an altitude test chamber as a safety measure such that heat in the chamber will not exceed its limit. A fixed temperature is entered into the control system. When the temperature in the chamber surpasses the preset temperature, the alarm activates.
Altitude test chamber testing is an essential part of the testing of products that can be influenced by changes in pressure. These specially configured and designed chambers are capable of easily simulating the effects associated with increased altitude by adjusting the air pressure in the chamber to meet the atmospheric conditions and circumstances of being on a mountain or flying.
Products that have a sealed case with a liquid or chemical as their contents may burst when subjected to high altitudes, which can become critical if the contents are acidic or harmful. By placing the sealed product in an altitude test chamber, the viability of the casing material can be determined as well as the pressure and height at which the casing will fail.
The implementation and use of test chambers have been for the perfection of products and to assess their weaknesses or points of failure. In the modern age, data collected by test chambers can prevent accidents and ensure the longevity of a product. Every aspect of natural environments can be recreated in a controlled method for evaluation, assessment, and examination.
Altitude test chambers are used to check the strength and weaknesses of instruments, machines, and devices that are required to operate under high pressure at high altitudes. Powering up a mechanical device to see if it remains operational at increased pressure and altitude can provide information regarding the ability of the device to perform its function when under pressure. In the case of aircraft and spacecraft, this aspect of the testing can be critical in preventing a malfunctioning component from being installed where it may fail. .
The array of tests and assessments that altitude chambers are capable of performing run the full gamut of products from ones for the home that may fail when pressure is applied to more important ones that are necessary to save people’s lives. As with all aspects of testing, high altitude testing provides data and information that can decide the success or failure of a product.
The multiple capabilities of altitude test chambers make it possible to vary the temperature in the chamber to match the parameters of different altitude conditions. In the majority of cases, altitude testing is completed at room temperature. This may not always be the case for implements since high altitude temperatures can vary in accordance with positioning and height.
To meet the needs of such testing, temperatures in altitude chambers can be adjusted from – 68° C up to 200° C to match the variations in temperature as well as the changes in humidity.
The reason for the rise in the use of testing chambers has been their ability to precisely create conditions that a product will confront during its use. Due to the critical nature of products, instruments, and components used at high altitudes, it requires more precision to ensure that the exact environmental parameters are being recreated.
Manufacturers of altitude test chambers work diligently in the development of control mechanisms that are capable of recreating the most minute details of pressure, altitude, climate, and atmospheres to match the requirements of a product and to determine its optimal level of performance.
Although conditions can be controlled from touch panels installed on the chamber, they can also be accessed from an offsite laptop or computer. Advancements in technology and new innovations in instrumentation have made it possible to program the exact details of an experiment and set the time for the adjustments to stop or be changed.
The reason for the use of altitude chambers for creating test conditions is that traditional pressure regulators are not capable of making the sudden pressure changes found at high altitudes. An altitude test chamber is necessary to achieve the steady pressure reduction to achieve the complex control algorithms. The many valves, pumps, and pressure instruments can only be precision controlled in an altitude test chamber.
An aspect of the control of altitude test chambers is the need for safety such that an experiment or test does not take the conditions to extremes that are beyond the parameters of its design. Every altitude chamber has a fail safe control that terminates the conditions when they reach a point at which they may be unsafe or detrimental to the chamber, the test material, or the surrounding conditions.
Safety features can be created in several ways, the first of which may be established by the manufacturer for the protection of the chamber and to ensure its performance. The second set of controls are in the hands of the technicians performing the tests who can enter the lower and upper limits of the test to avoid exceeding the requirements of the test and specifications of the chamber.
In its most basic description, an altitude test chamber is a form of giant computer that creates programmed conditions, controls and monitors those conditions and ensures that every aspect of the test is completed safely within the set requirements. As with any form of machine, it may have errors that need to be watched and controlled with safety measures.
A condition that is applicable to all test chambers is the control of airflow, which is necessary for the creation of the proper vacuum and pressure conditions. Airflow is one of the first elements that engineers examine when developing an altitude chamber since the pressurization of air is an essential part of altitude tests.
The control of airflow to fit the conditions and have the correct temperatures requires technical instrumentation and precise calculations. Included in the oversight of airflow is control of the amount of moisture to manage the humidity, which can grossly affect the testing outcomes.
The air circulation in an altitude test chamber has a downward flow similar to cleanrooms, which keeps the flow constant and even.
Altitude test chamber manufacturers are proud to point out how tightly sealed their chambers are to avoid contamination of the testing conditions. All chambers are welded on the outside and inside lining and carefully tested for any leaks, cracks, or unsealed openings. Highly trained professional technicians work diligently to ensure that the chamber is capable of flawlessly performing its function.
The enhancement of the seal on an altitude test chamber is created through the use of high grade steel and stainless steel to ensure a vapor tight interior lining. These factors are an essential part of all test chambers and altitude test chambers in particular.
The testing of the durability of products has existed for several years. It began in a crude fashion and rapidly advanced into more technologically sophisticated methods. Manufacturers use a variety of testing methods to ensure that the products they sell will be capable of meeting the demands placed on them by users.
Test chambers have been developed to assess the levels required by users of products and to determine to what extent products can withstand use. Common test chambers examine a product‘s reaction to inclement weather, extended storage, shocks or vibrations, and other potentially damaging conditions.
A specialized version for testing a product‘s endurance is an altitude test chamber, which has become more vital as the demands of the supply chain have increased. Small and highly technical products are being produced offshore and flown to factories for assembly. It is essential that the products are not damaged during transit since such harm affects production and other supply chain elements.
Altitude chambers have become a necessary part of evaluating potential problems that will affect a part that is air shipped. The technical designs of altitude test chambers make it possible for testing to replicate the exact conditions found at different altitudes. From the accumulated data, manufacturers make adjustments to their components and parts to overcome any difficulties.
A more crucial aspect of the need for altitude test chambers is their use in testing components, instruments, parts, devices, and mechanisms that are used in commercial aircraft and military aircraft where faulty instrumentation can lead to disastrous consequences.
Unlike hyperbaric chambers that are used to assist athletes, prepare flight crews, and create terrestrial altitude conditions, altitude test chambers simulate the precise conditions that an essential piece of aircraft equipment may encounter during a flight. As controls are activated in the chamber, technicians and engineers are able to observe the behavior of an instrument as the atmosphere changes. Any faults, irregularities, or failures are observed and recorded such that adjustments and changes can be made to meet the created conditions.
The wide selection of altitude chambers and their capabilities make it possible for any company that produces technical flight equipment to rent or purchase an altitude test chamber that exactly fits their needs. The precision controls and accuracy of the provided data have proven to be an exceptional assist in helping provide technical components that are fail proof and highly reliable.
When manufacturers produce products for critical industries, they must follow the regulations and standards that monitor and oversee the performance of their products for that industry. Several regulating agencies, from those that publish international standards to those that are published nationally, have stipulations regarding the testing practices for instruments and components that are used in airborne equipment.
The United States military, when having equipment contracted for manufacturing, has precise standards for materials to be produced and goes as far as to list the exact steps to be taken during testing. Included in the military regulations are the necessary requirements for test equipment, which are strictly adhered to by altitude test chamber manufacturers.
The ISO is an international manufacturers‘ guideline organization that has representation from over 150 countries. The committee for the organization meets regularly to establish standards and update the present ones.
ISO 7137 includes standards regarding the different environmental conditions and test procedures for airborne equipment. The main focus of the standards is regarding transport aircraft applications.
The EUROCAE was founded in 1963 to standardize processes and procedures regarding airborne and ground equipment and systems. EUROCAE ED 14 lists the minimum environmental test conditions for airborne equipment. The purpose of the tests is to examine the characteristics of airborne devices in representative conditions.
MIL STD standards clearly and succinctly outline the practices and procedures for testing equipment and materials for military use. The requirements are detailed and cover the minutious details of testing procedures.
MIL STD 810 outlines program planning and engineering for the examination of environmental stresses that would influence the performance of a component during its time of use. The substance of the standards outlines the kinds of real world conditions required for testing various systems.
The RTCA was founded in 1935 to provide technical guidance regarding all aspects of the air transportation industry. It is a non-profit membership organization that provides data and information to government and non-governmental organizations.
RTCA DO 160 outlines the environmental conditions and testing procedures for all airborne equipment. Since it is essential that aircraft navigation and communication systems operate flawlessly in a wide array of conditions, the RTCA has published a set of best practices for critical component testing.
DO-160 outlines the procedures necessary for testing airborne equipment. It was published in 1980 and is regularly revised to meet ever changing technological innovations. Altitude test chambers are capable of performing all of the required tests.
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