Environmental testing has nothing to do with an evaluation of the earth’s environment. Not the environmental testing we’re writing about here anyway.
Also known as environmental simulation, environmental testing involves putting your electronic product through environmental extremes and then determining what hardware failures occur. This process is crucial for pinpointing design flaws for ensuring the reliability and ruggedness of your equipment.
Environmental testing is split into two types: climatic and dynamic.
Climatic testing is performed in climatic test chambers. They range in size from desktop to hangar-sized. The McKinley Climatic Laboratory at Eglin Air Force Base in Florida is 55,000 square feet, and accommodates a hulking Lockheed C5 Galaxy transport aircraft.
Dynamic testing is performed on shakers and similar devices. It includes testing for shock, vibration, and earthquake/seismic. See a video of MET’s MIL-S-901D Hammer Shock rig being constructed and deployed.
Highly Accelerated Life Testing (HALT) is a form of environmental testing that combines climatic and dynamic components. It integrates vibration into the chamber environment, where temperature and humidity extremes can also be applied simultaneously. HALT is a faster, more effective version of the old environmental stress screening (ESS).
Testing should be conducted during the development of your hardware, so that all failures can be determined before the design is finalized. It is much better to fail during environmental testing than to fail in service, possibly causing user harm and often leading to warranty or recall expense.
With HALT, failure is a good thing, although it might not feel like it. It serves as a catalyst for redesign that improves the durability and ruggedness of the device, allowing you to lower your product’s infant mortality rate and reduce claims under your product warranty.
MET Labs owns and operates dozens of environmental test chambers and an impressive shock/vibe/seismic capacity in multiple locations across North America, as well as 24-hour HALT Testing on both coasts. Contact us for a free fast-response quotation.
The electromagnetic compatibility (EMC) requirements for telecom and military equipment are considered among the most difficult to meet for any industry. Not many electronics manufacturers conduct testing for both requirements, but it happens occasionally. For those who do, it’s an advantage to pursue both at the same time, as there is some overlap. Following is a short MET Labs overview on some of the primary similarities and differences.
MIL-STD-461 is the primary EMC standard for military approvals. The current version is MIL-STD-461F, but previous versions may still be specified in U.S. military contracts.
GR-1089-CORE is the primary EMC standard for telecommunications (NEBS) equipment. The current version is Issue 6.
MIL-STD-461 is similar to section 2 and 3 of GR-1089 in that they both include EMC conducted and radiated emissions and susceptibility requirements, however the test methods are quite different.
For emissions, MIL-STD-461 requires use of a peak detector and the limits are more stringent for some platforms, like Army Ground. On the other hand, the radiated emissions test method could be considered less thorough because the test antenna and EUT are placed in one position, while for GR-1089 radiated emissions, the EUT is rotated 360 degrees and the antenna height is adjusted to find the maximum radiated emissions.
For susceptibility testing, MIL-STD-461 test method CS114 is similar to GR-1089 conducted susceptibility. Test method CS115 is somewhat similar to GR-1089 section 2 EFT. RS103 is similar to GR-1089 radiated susceptibility, however, for some military platforms, the test level is much higher than GR-1089 (up to 200V/m).
MIL-STD-461 does not include ESD testing, although many military test programs include IEC 61000-4-2 ESD testing along with -461. GR-1089 includes ESD testing in section 2 and references IEC 61000-4-2 for the test procedure.
Another occasionally-referenced military standard – MIL-STD-1399-070 DC Mag Field – is not like any GR-1089 test. This is a 1600A/m DC field, which is quite strong. If the EUT has no magnetic sensors, compass, or other magnetically sensitive components, it shouldn’t be a problem. If the EUT does have those components, it would have to be specifically designed to withstand this test.
MIL-STD-461 is the standard that defines the test limits, test levels, and test procedure for various electromagnetic phenomena for electronic equipment used by the U.S. Army, Navy, and Air Force on all platforms (ground, sea, and air). MIL-STD-461F is the latest version. Following are answers to common questions about this often-utilized military EMC standard.
Where can I find MIL-STD-461 and how much does it cost?
The standard is free and approved for public release. It can be downloaded from a number of sites, but we recommend using the official U.S. Defense Logistics Agency (DLA) ASSIST site. This site requires registration and a wait for approval.
What is included in MIL-STD-461?
Test methods cover electromagnetic emissions, which are an unintended, but unavoidable byproduct of every electronic device, as well as electromagnetic susceptibility, which is a measure of the equipment under test’s (EUT) ability to withstand electromagnetic disturbances.
Test methods include specific types of conducted, radiated, transient, and continuous emissions and susceptibility tests. See a full list of test methods on MET’s Military EMC Testing page.
The first few sections define general aspects of the standard and testing, such as terminology, test facilities, test equipment, setup of the EUT, applicable tests for equipment to be used on various platforms, etc.
Section 5 contains a test procedure for each test method, which defines the test equipment needed, instructions for setup, and a procedure for how to conduct the test.
Is compliance with MIL-STD-461 mandatory?
MIL-STD-461 is usually only required when part of a specific military contract between the U.S. military and an electronic equipment manufacturer.
The contract would specify the specific test methods within -461 which need to be performed and passed by the equipment being built for the military.
MIL-STD-461 testing is sometimes voluntarily performed by electronic equipment manufacturers for marketing purposes, to attract possible military contracts and/or for quality purposes, to ensure a rugged design.
I want to voluntarily perform MIL-STD-461 testing and am not worried about my EUT’s susceptibility to electromagnetic disturbances. What are the best test methods for determining compliance with the standard’s electromagnetic emissions requirements?
CE102 and RE102 are the most applicable test methods for this.
CE102, conducted emissions, power leads, 10 kHz to 10 MHz, is performed to verify that electromagnetic emissions from the EUT do not exceed the specified requirements for power input leads, including returns.
This will ensure that the EUT does not cause interference to other electronic equipment operating from the same power source, since the emissions can conduct along the supply lines.
A special piece of test equipment called a line impedance stabilization network (LISN) is connected in series with each conductor of the input power lines to the EUT.
The LISN establishes a 50 Ohm impedance on the power line and has a coaxial measurement port, which allows for connection to a 50 Ohm spectrum analyzer for measurement of the RF emissions.
The EUT is exercised in a way typical of its normal use and the emissions are compared to the limit. If CE102 emissions exceed the limits, the tests are considered not compliant.
RE102, radiated emissions, electric field, 10 kHz to 18 GHz, is performed to verify that electric field emissions from the EUT and its associated cabling do not exceed specified requirements.
This will ensure that radiated emissions from the EUT do not cause interference to other electronic equipment operating nearby.
The EUT and test antenna are set up within a shielded test enclosure, which is internally lined with RF absorbent material.
The shielded enclosure prevents RF ambient noise from entering the test area, while the RF absorbent material reduces RF reflections from the metallic chamber walls, allowing for accurate radiated RF measurements of the EUT emissions with a test antenna.
The test antenna is connected through coaxial cable and chamber wall bulkhead connectors to the spectrum analyzer outside the test chamber.
The EUT is exercised in a way typical of its normal use and the emissions are compared to the limit. If RE102 emissions exceed the limits, the tests are considered not compliant.
For MIL-STD-461 testing for marketing purposes only, does MET issue a test report?
MET can issue a test report and a one-page certificate upon completion of testing.
The test report and certificate would not guarantee acceptance of the product by the U.S. military. However, you are free to use your engineering judgment to make claims of compliance for similar projects, based on the test report and certificate provided.
MET Labs has a reputation for high quality test results and our test reports will increase the credibility of your marketing claims.
Request a free quotation for MIL-STD testing for military or marketing requirements.
The U.S. Department of Defense (DoD) recently issued Change Notice 1 to MIL-STD-810G, Environmental Engineering Considerations and Laboratory Tests. This change notice incorporates more changes – climatic and dynamic – than any previous revision of -810.
A PDF of Notice 1 is available here. It’s a bulging 1,058 pages, over 280 pages more than the Revision G alone and more than twice as many pages as Revision F. Changes are marked by lines in the margins.
Major changes include:
- In Part 1, a significantly expanded section on the Life Cycle Environmental Profile (LCEP)
- In Part 2, all test methods – 500 through 528 – have been updated with a new note
- Only Method 528 can be called out in blanket fashion now
- A rewrite of mechanical shock
- Additional guidance in combining procedures
MIL-STD-810 is used by both the U.S. military and industry to assure that the environmental design and test limits of equipment match the requirements that equipment will face in actual use.
Whether a military product must be tested to Change Notice 1 is dependent on the DoD contract. The DoD uses the product’s life cycle environmental profile and its anticipated deployment region to determine which standard version to specify.
MET Labs is an elite 3rd Party Test Lab for Military and Commercial Aircraft equipment testing, and has top-flight experience working with every top defense contractor and commercial aircraft manufacturer and many of their suppliers. Contact us for a rapid-response quote for EMC or Environmental Simulation testing.
Some Military EMC testing projects are routine. This post describes a recent one that wasn’t.
Hydraulics International, Inc. asked us to test its four-wheeled 2-ton hydraulic power generator (pictured in MET’s Military EMC chamber), which is used to check the flight control of the Bell Boeing V-22 Osprey. The V-22 Osprey is well known for its Rolls-Royce engines that tilt, allowing it to take off like a helicopter and fly like an airplane.
The test plan was based on MIL-STD-461F, but MET was able to get approval on a couple deviations to save the customer time and money.
The first deviation was to decrease the unit’s RPM during testing. The test procedure called for measurements taken at 2,500 RPM, but MET was able to justify a lower RPM by proving that the unit’s electronics would not be affected by its engine speed. This deviation was important because the EUT’s 160 HP diesel engine would heat the military test chamber rapidly when run at high RPM.
The second deviation was for test method RS101, which normally requires many close proximity measurements using a small radiating loop sensor. For this large EUT, a non-deviated test plan would have required 60 hours’ worth of testing just for RS101. MET was able to acquire a deviation from the Navy by getting permission to take measurements only near the unit’s electronic control panel.
A challenge that did not require a deviation was how to exhaust the diesel fumes out of the test chamber, while maintaining the 200 V/m EMC chamber’s RF shielding effectiveness. Radiated emission ambients were shielded by using a small diameter steel exhaust tube that was secured to the chamber ceiling using metal-to-metal bonding techniques.
This project also required Data Item Description (DID) documentation. Read more about DID documentation, its benefits, and process on the bottom of this Military EMC testing page.
Have an upcoming MIL-STD-461 test requirement? Ask about MET’s complimentary MIL-STD-461 Pre-Testing Program, which greatly increases your chance of first time compliance. Contact us today.
Most Military/Avionic EMC test programs include radiated emissions testing. This is the test method where the unintentional emissions which
radiate from a piece of electronic equipment under test are measured with an antenna and spectrum analyzer and plotted against the required limit. One issue which must always be dealt with during radiated emissions and other EMC test methods is control of the ambient emissions. Ambient emissions such as television, radio, and wireless signals are attenuated by the shielded EMC test chamber; however, they can travel into the chamber on the cables which connect to support equipment outside of the chamber.
If ambient emissions are not mitigated, they can appear as an EUT failure during testing. One way to deal with this issue proactively is to use shielded cables with shielded bulkhead connectors or feed-through capacitors (Figure 1) to decouple the ambient signals to ground.
In Figure 2, note how the ambient emissions exceed the Army ground limit at 28MHz when the power and signal
cables pass directly through an oversize chamber hole. In Figure 3, see how the ambient emissions have been attenuated below the noise floor of the measurement system, due to power cables connecting through 1uF feed-through capacitors and the shielded serial cable connects through a wall-embedded bulkhead connector.
Utilizing our machine shop, steel panels, and a variety of connectors, MET Labs provides custom bulkhead panels for all military and avionics test programs, at no additional cost to the customer.
Similarly, some electronic equipment requires water as part of its normal mode of operation, such as aircraft
galley equipment or water-cooled high power equipment. MET has installed regulated water at its Military/Avionic EMC test chambers using bulkhead fittings that maintain the shielding effectiveness of the chamber. MET has a variety of hoses and fitting available and trained staff to provide professional hookup to the equipment under test. This too is a free service provided to all MET customers.
Visit our quote center for an immediate EMC testing need, or Ask Pat, our resident electrical product compliance expert, for questions relating to chamber pass-throughs for water pipes and power & signal cables.
Although it was developed by the United States military, MIL-STD-810 is a test methodology that is used by many manufacturers now, regardless of whether they plan to sell to the U.S. Department of Defense.
MIL-STD-810G allows for tailoring an equipment’s environmental design and test limits to the conditions that it will experience, also known as ruggedizing a product.
Depending on the ruggedness requirement of a product (dictated by where and how it will be used), models have different pass criteria.
Within the computer laptop industry, three marketing categories are used to characterize the durability of business laptops: business-rugged, semi-rugged, and fully rugged.
A business-rugged laptop will typically feature a magnesium alloy chassis with shock-resistant hard drives and spill resistant keyboards. They are tested for shock, vibration, drops, low pressure, blowing sand, low/high temperatures, humidity, liquid spill and domestic dust.
Semi-rugged devices feature additional protection including display protection, outdoor viewable display and port covers. They go through the same tests as business-rugged laptops, but are exposed for a longer test period, or have higher pass criteria.
Fully rugged laptops have to survive the most extreme conditions. These systems must withstand higher drops, more vibration, temperature shocks, intense rain, salted fog, explosive atmosphere, blowing sand/dust and function at a wider range of temperatures than less rugged devices.
In addition, most fully rugged systems pass a variety of other certifications such as IP-65 for ingress protection, ANSI/ISA 12.12.01 for hazardous locations, and MIL-STD-461F for resistance to electromagnetic interference.
Despite some reports to the contrary, the Federal Aviation Administration (FAA) and the European Aviation Safety Agency (EASA) will accept RTCA/DO-160 commercial aircraft equipment test reports from accredited and non-accredited labs.
Accreditation is a 3rd party assessment of a laboratory’s quality systems, processes, and documentation. Accreditation assures a minimum level of competence, but it does not guarantee competence to properly perform particular tests and to provide bullet-proof documentation.
More important than accreditation is experience. Does a lab have skilled, experienced, and knowledgeable engineers and technical writers? Does a lab have experience testing similar equipment to the same standards?
Here are 4 key items to keep in mind:
- Understand what your customer and regulatory agencies require. For example, FAA may require witnessing by an approved DER or DAR.
- Develop a solid test plan and follow it closely.
- Witness testing. No one knows better than you how the EUT is operated, wired, and configured.
- Make sure everything is documented meticulously: photos and descriptions of setups, test equipment (including calibration information), and test results.
Register for an upcoming free webinar on RS105 EMP Immunity Testing.
A draft of Revision G of MIL-STD-461 has not been released yet, but MET Labs has obtained information about proposed changes to the Military EMC test. As covered in this previous post, one of the primary changes is the incorporation of indirect lightning testing heavily leveraged off of Section 22 of RTCA/DO-160G. There is no lightning requirement in MIL-STD-461F, which was released in 2007.
There is one test that is very likely to be added to MIL-STD-461G: CS117
There are two additional tests that are being considered, but are much less likely to be included: RS106 & RS108
Information about the CS117 test:
- Derived from DO-160 Section 22 lightning induced transient susceptibility
- Includes Multiple Burst/Single Stroke same as DO-160
- Idea is not to change waveforms; services (Army, Navy, Air Force) would need to control the application
- Cable injection only – no pin injection testing
- Limited applicability (aircraft electronics) based upon specific program contact call out
Information about the RS106 test:
- Similar to RS105 (EMP free field test for equipment)
- Limited applicability – mainly for external stores (missiles, pods, ground equipment, etc.)
Information about the RS108 test:
- Similar to RTCA/DO-160 Section 23 Lightning Direct Effects
- Limited applicability (antennas or other external located items) based upon specific program contact call out
The rollout of MIL-STD-461G is currently scheduled for an initial draft in June 2013, a final draft in September 2013, and release in Fall 2014.
Want to know more about upcoming changes to MIL-STD-461? Consider attending one of these events:
In two days, MET is hosting a MIL-STD Testing Seminar in Santa Clara, California.
Next week, attend this Lightning Testing Webinar.
In August, Pittsburgh is hosting the EMC Symposium, where MET Labs is exhibiting in booth #1024.
Or contact us with questions or a quote request.
We often get the question: What version of RTCA/DO-160 should I use?
As per usual, it depends. RTCA/DO-160G, Environmental Conditions and Test Procedures for Airborne Equipment, is the latest version; it is dated December 8, 2010. According to an Advisory Circular dated June 22, 2011 from the U.S. DOT Federal Aviation Administration, “The FAA strongly encourages the use of RTCA/DO-160G for new articles.”
However, if the Technical Standard Order (TSO) does not specify the environmental qualification, the applicant may choose any environmental standard conditions and test procedures appropriate for their airborne equipment.
If the TSO does specify a version, you may request a deviation, in accordance with the requirements of 14 CFR part 21 subpart O, to use the conditions and procedures in a different version of RTCA/DO-160.
If the version of RTCA/DO-160 specified in a TSO is version D or later, and an applicant wishes to use a version prior to RTCA/DO-160D, then the applicant must meet the requirements of paragraph 6a by comparing the specific procedure and category changes, section by section, between the two versions. The applicant must also address the differences between the two test results when providing an equivalent level of safety.
When a new application is based on the design of an existing approved article, the applicant may ask to use environmental test data from the existing article’s environmental qualification, based on similarity between the two articles. This request must be fully supported with a detailed similarity assessment comparing the changes from the earlier approved article to the article in the new application. The aircraft certification office (ACO) may accept the data if the similarity assessment clearly shows that the design changes will not adversely affect the environmental qualification.
If you are an applicant installing equipment, you may use RTCA/DO-160, any version, to support compliance with the appropriate airworthiness requirements except as identified in paragraphs 7c, 7f, 7g, and 7h.
When installing equipment previously qualified to other environmental standards, such as MIL-STD-810G, the equipment must comply with applicable airworthiness requirements. You may use DO-160G to do a comparison analysis to show that it provides an equivalent level of safety in the expected operating environment.
Some of the environmental conditions and test procedures contained in RTCA/DO-160 such as waterproofness, sand and dust, or salt fog, may not be applicable to your installation based on intended location of the equipment. You must determine which sections and categories are applicable to your specific project.
About RTCA/DO-160: The airborne equipment standard, and its precursor RTCA/DO-138, has been used since 1958. Its purpose is to show compliance with certain airworthiness requirements. It is not the intent of RTCA/DO-160 to be used as a measure of service life of the airborne equipment subjected to these tests. The standard was developed by RTCA SC-135.