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.
At this week’s 2011 International Symposium on Electromagnetic Compatibility in Long Beach, CA, Fred Heather of the US Navy in Patuxent River, Maryland, gave an overview on the proposed addition of electrostatic discharge (ESD) and lightning testing to MIL-STD-461. Heather is the Electromagnetic Environmental Effects (E3) Lead for the U.S. government’s F-35 Joint Strike Fighter Program.
Currently, MIL-STD-461 is at revision F, so the new standard version will be MIL-STD-461G.
The changes propose to add four additional tests:
These tests are primarily based on the requirements from RTCA/DO 160 sections 22 and 23.
These changes are largely being driven by the use of composite materials in airframe construction, including that used in the Boeing 787 Dreamliner and Airbus A380. Many composites don’t conduct lightning currents the way metal airframes do, leading to the possibility of higher voltages and currents affecting aircraft equipment.
The changes were proposed for revision F, except the Navy and Air Force reportedly couldn’t agree on pin injection testing, thus delaying its implementation.
Read more about the requirements of MIL-STD-461 and other military EMC tests.
Due to industry demand, iNARTE is launching two new EMC certifications this year:
- MIL-STD EMC Specialist
- EMC Design Engineer
This is in addition to its existing certifications:
- EMC Engineer
- EMC Technician
- ESD Engineer
- ESD Technician
- Product Safety Engineer
- Product Safety Technician
MIL-STD EMC Specialist
iNARTE’s EMC Engineer and Technician certification programs began 27 years ago as a result of requests from NAVSEA and the U.S. Navy to identify experts who could resolve EMI issues in the fleet. As the years went on, the iNARTE certification program took on a wider appeal, and today these certifications have less than 20% military content. The new MIL-STD EMC Specialist certification refocuses emphasis on this military legacy.
EMC Design Engineer
Attention has shifted to EMC Design Engineering as manufacturing and some of its associated product testing has moved to lower labor cost regions. When that happens, product design and development often remain at company headquarters in the developed region. Thus, in some areas, there is an increased emphasis on EMC design.
For the EMC Design Engineer, there are three levels of certification:
- EMC Design Engineer – for those employed for less than three years
- Senior EMC Design Engineer – for those with four or more years of experience
- Master EMC Design Engineer – reserved for grandfathering of acknowledged experts
The first examination for the EMC Design Engineer level will be administered August 19 in Long Beach, CA at IEEE International Symposium on Electromagnetic Compatibility 2011, where MET Labs will occupy booth #340.
iNARTE certifications are not required by regulators or accreditation agencies; rather, they are a good differentiator for professionals, and are viewed favorably by hiring manufacturers and test labs.
iNARTE (formerly NARTE) is a nonprofit, professional credentialing association which certifies qualified engineers and technicians in the fields of Telecommunications, Electromagnetic Compatibility/Interference (EMC/EMI), Product Safety (PS), Electrostatic Discharge control (ESD) and Wireless Systems Installation.
With the recent news that the U.S. President’s $223 million “doomsday plane” is protected from electromagnetic pulse (EMP) came the inevitable questions. What is EMP and how is it created? How can a plane with a reported 165,000 pounds of state-of-the-art electronics possibly be protected from such a sinister attack?
EMP & Its Creation
EMP is a high amplitude, short duration, broadband pulse of electromagnetic energy which can have devastating effects on unprotected electronic equipment and systems.
The electromagnetic pulse effect was first observed during the early testing of high altitude airburst nuclear weapons. During the explosion, gamma rays (high energy photons) are rapidly released in all directions from the blast. These gamma rays interact with air molecules in the earth’s atmosphere, which creates electromagnetic energy. This interaction process is called the “Compton Effect.”
Energy of these pulses disperse across a broad spectrum, but the majority of pulse energy resides in the frequency spectrum of 10MHz-100MHz. For a large quantity of electronic equipment, this is the operating range and hence the greatest risk. Peak field strengths are estimated to reach into thousands of volts.
Non-nuclear EMP technologies – called “Directed Energy Weapons” – are increasingly being developed. They are capable of graduated effects on electronics ranging from disrupting operation, to permanent damage, and complete destruction. These weapons include:
- Arc Discharge EMP Generator
- Flux Compression Generator (FCG)
EMP Immunity Testing
The RS105 test method specified in MIL-STD-461F addresses the risk of radiated exposure to an EMP event. The U.S. Navy, among other military branches, requires RS105 testing for nearly every installation platform, from surface ships, submarines, and aircraft, to ground applications.
The test follows this procedure:
- Start at 10% of specified level
- Verify waveform
- Apply pulse 5 times at the rate of not more than 1 pulse per minute
- Rotate equipment under test (EUT) 90 degrees, and pulse 5 more times
- Rotate another 90 degrees and pulse 5 times
- Monitor for signs of degradation
The purpose of RS105 testing is not to damage the equipment, but to determine its immunity threshold to the electromagnetic pulse.
Hollywood’s Take on EMP
Last, and most important, was the EMP attack, or “pinch,” featured in the 2001 movie Ocean’s Eleven possible? If you remember, George Clooney and his fellow con artists utilize a “Z-pinch” that detonates an intense electromagnetic pulse that blacks out Las Vegas’ entire power grid for a few moments (in order for them to sneak into a casino vault).
No, says Sandia National Laboratories, owner of the world’s most powerful Z-pinch. The super-charged electrical generator creates a rainbow spectrum of intense x-rays, but a feeble EMP.
Read more about RS105 and other military electromagnetic compatibility (EMC) tests.
For manufacturers of products that require military standard (MIL-STD) testing, but have more of a commercial than military application, it pays to explore whether the product can be exempted from restrictive provisions in the Arms Export Control Act and the International Traffic in Arms Regulations (ITAR).
If after reviewing the U.S. Munitions List and other relevant parts of the ITAR, in particular ITAR §120.3 and §120.4, you are unsure of the export jurisdiction of an item or service, you should request a Commodity Jurisdiction (CJ) determination from the U.S. Department of State.
Some resources to help with the application:
- All CJ requests must be submitted electronically using the 5-page DS-4076 CJ request form
- FAQs regarding the CJ process
- For general questions on CJ, contact the Response Team at (202) 663-1282 or DDTCResponseTeam@state.gov
Applicants are not required to be listed with the U.S. Department of State’s Directorate of Defense Trade Controls to submit a CJ request. Following a successful submission and electronic confirmation receipt, the applicant will receive a Commodity Jurisdiction case number via email within 48 hours.