NTS News Center

Latest News in Testing, Inspection and Certification

NTS News Center - Latest News in Testing, Inspection and Certification

NTS offers CAD/FEA Modeling for Direct and Indirect Effects Lightning, Reducing Test Costs and Time

The NTS Lightning Technologies laboratory in Pittsfield, MA is now offering finite element analysis, allowing the performance of complex simulations that accurately model the interaction of lightning with a variety of aircraft and avionics components for our customers. This service is available to all of the customers of the 10 NTS facilities across the US offering direct and indirect lightning testing.

Lightning Testing Figure 2

Figure 1 – Current Distribution and Magnetic Field in Two Current Carrying Copper Conductors

By decomposing complex CAD-generated objects into meshable geometrical shapes, these models are able to accurately portray the lightning environment (current distribution, electric and magnetic fields, pressure waves, temperature variations, induced transients) on high fidelity renditions of real objects. Once the geometry is built, highly customizable material parameters, boundary conditions, and applicable physics interfaces (Maxwell’s Equations) are applied that generate a system of equations that is solved in COMSOL. With accurate representation of test object geometries, the solutions of these models allow for conducted and induced transients to be determined at any point in the model.

Figure 2 - Magnetic Field Penetration through Apertures on a Fuselage

Figure 2 – Magnetic Field Penetration through Apertures on a Fuselage

Utilizing simulation and modeling along with laboratory testing provides customers with a new, cutting edge way to obtain valuable test data that can reduce testing costs substantially. Making use of these models allows for the easy acquisition of difficult or impossible to obtain lab measurements (equipment limitations) without having to perform the test on an actual object. Once a model has been developed, a similar test is performed on a real piece of equipment in order to validate the model. Once the model has been validated, lightning attachment locations, cable routing configurations, and material characteristics (to name a few) are all easily modifiable to allow for many permutations of the test environment to be modeled. The results of these models can provide valuable design constraints and necessary test levels for certification. Additionally, once validated, these models can serve as a firm basis for similarity analyses for future design changes, providing the potential for a cost and schedule reduction to future programs.

Figure 3 - Magnetically Induced Voltage on Conductor inside Fuselage

Figure 3 – Magnetically Induced Voltage on Conductor inside Fuselage

For questions about our new finite element modeling and how it can be applied to your testing program or for any other lightning test related inquiries please contact our General Manager Mike Dargi at 413.499.2135 or Mike.Dargi@nts.com

NTS has 10 facilities across the US capable of performing your complex direct effects and indirect effects lightning testing. We are able to meet the full scope of RTCA DO-160 testing, as well as numerous other specifications with lightning requirements including MIL-STD-461/462, SAE ARP 5416A, and IEC 61400-24 (wind turbines). Contact us today to discuss your next test program.

How can I relate the results of MIL-STD-810 salt fog testing to the life time of my product?

This is a very common question that we get asked quite often and unfortunately there is no correlation between what the product sees in the salt fog chamber to what it will experience out in the field. In order to understandSalt Fog Testing why, you must first understand the purpose of the test.

Originally stated by V.J. Junker in The Evolution of USAF Environmental Testing(1), the test is to determine the resistance of aerospace ground and aerospace equipment to the effects of a salt atmosphere.

According to Mil-STD-810G, the test is performed to determine the effectiveness of protective coatings and finishes on materials. The stated purpose of the test is to determine design flaws such as dissimilar metals, improper coatings, uncoated materials, electrolytic action, binding of parts, etc. Therefore, results can be related to the suitability or quality of parts or assemblies, but cannot be directly related to exposure time in the marine environment.

Salt Fog and Salt Spray testing are conducted at 14 NTS locations across the country. Visit our locations page to find the lab closest to you!

(1) Junkers, V.J. The Evolution of USAF Environmental Testing, Technical Report AFFDL-TR-65-197, October 1965.

Is there a preferred sequence for EMI, EMC Tests?

EMI Testing NTS BoxboroughOne of the questions we get asked often is about order of EMI/EMC testing.  Neither MIL-STD-461 nor RTCA/DO-160 specify the order of test performance.  Leaving aside the issue of Safety of Flight tests for aircraft (which typically must be performed prior to any other testing), there are a few different approaches to take in this regard.

The first approach is to perform an analysis of the equipment under test (EUT) before going to the lab to determine what tests are most likely to cause problems, and to start with them.

This approach works best if a customer does not have any idea how their product will stand up to the EMI/EMC compliance requirements. A design analysis tends to vet out significant concerns up front, potential design solutions can be discussed prior to qualification testing. At this point, the Subject Matter Expert (SME) should be able to prioritize the threats, and work with the customer to develop a suitable test order. This approach also provides an opportunity for pre-qualification evaluations to ensure the product will not have any issues during the qualification program.

The second approach is to begin with the most benign tests, usually the emissions.  These tests have virtually no chance of harming the EUT, but they sometimes prove to be the most problematic.  Emissions testing tends to reveal inerrant design flaws the most, and generally requires some level of redesign. Changes in design could necessitate repeating other tests if emissions is not completed first. However, there may be cases were a customer feels their product does not have any emissions concerns but is likely to be susceptible to a particular immunity test. They may choose to get the immunity evaluation out of the way first, and allow time for potential modifications prior to commencing with the remaining tests. This approach would also avoid costly retests or delays due to changes to the EUT.

The third approach is to begin with the most potentially damaging tests first. The philosophy here is that all is well and good if the EUT endures those tests with no issues.  However, if there are susceptibilities that require repair/redesign, those problems can be resolved before continuing with the other tests.

In summary, the EMC / EMI testing sequence used should be an iterative decision between the lab and the customer to determine which approach best suits the product and customer’s needs.

NTS Quick Guide to Reverberation Testing

Picture4

Inside the RF chamber

A reverberation chamber (mode tuned/mode stirred chamber) is a shielded enclosure or resonant cavity for RF testing which is statistically isotropic, random polarity, having RF uniformity within specified limits. Typically it has a paddle (or tuner) which stirs up the field, randomizing the boundary conditions. Mode tuned is where the paddle is stepped to a position and then RF is applied for a dwell time sufficient to exercise the equipment. Mode stirred is when the paddle is continually turned with RF energy applied for a full paddle revolution. Reverb chambers are useful for radiated susceptibility, radiated emissions (total radiated power), shielding effectiveness, and many other troubleshooting scenarios.

The benefits to reverberation testing are numerous. RF is applied to all exposed sides of the device under test (DUT) during a full 360° turn of the paddle, instead of a single side. For direct illumination testing, many standards require the all apertures of the DUT to be illuminated. On complex items this can be difficult – even impossible. Window effects testing, required when applying direct illumination, is not required during reverb testing because the field intensities are constantly changing. SAE ARP 5583 states that the reverb is the recommended and preferred method to show compliance for large and/or complex Level A (flight critical) systems. Test repeatability is much easier to obtain in a reverb chamber with proper processes, and running the test is much less complex than a single aspect angle test. Antenna distance, aim (focus), 3 dB beam width, location of the field probe, EUT layout, and location of the EUT in the working volume are all less of a factor in the repeatability of test.

Picture6

A view from outside

You should know if reverberation testing is right for your program. Reverb chambers are random in polarity which makes it challenging in determining directivity of RF energy. Testing multiple field levels on a system, such as outside the pressure vessel level and inside the pressure vessel level, can be difficult; all equipment in the chamber is exposed to the same field. There are limitations on pulse width due to a high Q (efficient) chamber having large amount of stored energy. If you have small, simple equipment, single aspect angle tests may be faster and sufficient for test coverage. There are ways to compensate for each, and an NTS engineer can help with suggestions or assist you with a test plan.

Both direct illumination and reverberation test methods are acceptable paths to certification. They both have benefits and drawbacks that champion each as a test method. Fortunately, NTS has the ability to test in both methods and the engineering expertise to support your path to certification.

For more detailed information about reverberation testing at NTS Rockford, Fullerton, Plano, Tempe, or Boxborough, call 800-270-2516 or email us at sales@nts.com. Request a quote today!

MIL-STD-461G Released

MIL-STD-461 Testing at NTS

The G revision of the MIL-STD-461 standard was released in December 2015 and is available here. NTS’s Jeffrey Viel’s wrote an article for InCompliance Magazine reviewing the proposed changes which was published back in August 2015. These changes have carried into the final released standard and are worth reviewing.

A few highlights of the MIL-STD-461G standard:

  • FFT receivers are now permitted for use
  • Interconnecting cable routing now specified for floor standing equipment
  • Test method CS106 has been removed
  • Test method CS114 system check updates
  • The addition of test method CS117, conducted susceptibility, lightning induced transients, cables and power leads
  • The addition of test method CS118, personnel borne electrostatic discharge
  • Test methods RE102 and RS103 technical updates

Contact NTS today to discuss your next MIL-STD-461 test program.

The Benefits of Pre-Compliance EMC Testing

EMC Pre Compliance Testing

One of the biggest product development challenges today is ensuring electromagnetic interference is optimally controlled. With proper electromagnetic compatibility (EMC) testing and design, you can ensure the correct operation of various devices in the same electromagnetic environment. EMC is achieved by addressing both emission and susceptibility issues by taming the sources of interference and by strengthening the potential victims.

EMC Testing

A number of international EMC standards are in place to standardize product EMC performance. The FCC and CE are two of the most common EMC standards. Electromagnetic compatibility testing is broadly divided into
emissions testing and immunity testing.

EMC Emissions Testing

EMC emissions involve two types of testing: radiated emissions and conducted emissions testing. With radiated emissions tests, the goal is to check for unplanned emissions that exceed a given pass band as defined by the class of the product. Conducted emissions testing involve shorter frequency range — for example, 30 Hz to 10 KHz.

EMC Immunity Testing

Immunity testing is required for EMI compliance in the U.S. for medical devices and for a wide range of consumer products in the EU. A number of immunity tests may be required depending on the type of device and its application.

Pre-Compliance EMC testing

EMC testing is time-consuming, and failed tests can delay product launches. Your budgets will be stretched, and your reputation is at stake if you are not meeting customer’s demands. Many devices fail during EMC testing, often during radiated emissions testing.

By building EMC testing into the product design and development phases from day one, one can build a product that has a lower risk of failing EMC tests at the end. With pre-compliance EMC testing, you perform EMC tests and incorporate best practices throughout the design and development process. This allows you to meet EMC compliance more easily and effectively during your final testing.

Pre-Compliance EMC Testing Is Important

The best way to avoid expensive retesting and noncompliant EMI issues is by checking for emissions from your device throughout the product development cycle. Pre-compliance EMC testing has multiple benefits.

  • Detect Errors Upstream in the Product Development Cycle

product-development-cycle-table

The earlier in the product development cycle you can identify issues with emissions, the easier it is to correct the issues. Also, the solutions or options to correct EMI are more in the early stages of product development versus later. Correcting EMI issues after compliance testing is costly and results in loss of precious time versus fixing upstream in the design phase.

Imagine leaving EMC testing of your device at the end of the development of the product. Any issue that may have been smaller and possibly easier to isolate early on is now more complex and amplified due to more parts and subsystems within your device. For example, it’s much cheaper to make an EMC fix on a circuit board versus correcting once the design is final. As a specific example, a resistor-capacitor low-pass filter on data signals before crossing a radiating cable may cost you .1 to .5 cents per PCB. However, if the PCB is finalized and you need to solve against the radiating cables, a cable choke will cost you more than $1 per cable.

Mechanical changes, EMI shields, use of EMC foam and other design changes are made to counter emission issues. When EMC testing is done early, it allows you to make better decisions on types of changes to make to become EMC compliant.

  • Integrate Pre-Compliance Testing Into Product Development

When testing is integrated into product development, one can tap into a well-known testing company for ongoing support. It can provide testing infrastructure and subject matter experts during the entire product development cycle. This is an upfront investment that pays off by keeping your project on time and by reducing risks from noncompliance.

Experienced design engineers that offer pre-compliance EMC testing as part of their suit of services will continuously look for areas of risk during product development. For example, testing during product development can provide the designer options to add in preventative measures in the form of additional circuitry, or other mechanical or system design changes. When product designers come up with a fix, it is helpful to test it immediately before making major design changes.

  • Eliminate Overdesign

If you are not performing pre-compliance EMC testing, you may be overengineering your product to ensure it meets EMC compliance at the end. Since you are not testing along with design and development, you may be adding countermeasures which may be redundant. These measures may considerably add to your product cost.

Overdesign or overengineering is common across various industries. This can include coding for software, designing automobiles or airplanes, or design of bridges and building structures. With pre-compliance testing, you have the option to test more often and throughout the design and development. This can help you to avoid using parts with higher-than-necessary specs or even avoid parts you may be incorporating to stay EMC-compliant.

  • Design for EMC Compliance

This is not a test, but it’s one of the most ignored pre-compliance strategies. You can do a detailed and systematic schematic and layout design review as part of your pre-compliance processes. This can significantly reduce the risk of your product failing at an EMC test lab.

You can detect many potential emissions and immunity issues in a design review. A solid design review will catch many of the root causes of emissions and immunity problems even before your first test PCB is created. If you do not have in-house expertise for EMC-compliance design, work with a testing company that can provide this service. This can increase your first-time pass rate.

Pre-Compliance EMC Testing Options

Pre-compliance EMC testing can be done by hiring a testing lab or by doing it on your own once you have the right equipment and testing gear.

  • EMC Testing Lab

You can rent equipment and hire personnel from a testing company for pre-compliance testing. Professional testing labs have fully compliant test gear, which will allow you to perform tests with high accuracy. A reliable test lab will also be able to assess your test device and provide recommendations on potential root causes. This way, you can focus on addressing those as part of your pre-compliance effort. Some labs can provide turnkey pre-compliance and final compliance services as one package, which can keep your overall costs low.

Advantages to this approach include:

  • Your test results have a high level of accuracy since the same testing equipment is also used for final compliance testing
  • You don’t need to invest capital to procure test equipment
  • You get absolute measurements when performing emissions testing. If you do this on your own, you get measures which are relative

About NTS’s EMC Testing

NTS offers a wide range of services to help clients meet EMC compliance across various industries – consumer, industrial, automotive, medical, military, space, aircraft, telecommunications, etc. Our range of EMC/EMI services includes engineering, design analysis, testing and technical training.

NTS also has the largest network of commercial EMC testing labs in North America. We have a deep knowledge of various EMC compliance standards, and we are fully versed in FCC and CE standards and testing requirements.

Our labs and equipment use the latest technology and are powered by the most respected and experienced engineers and technicians. We have people, processes, tools and knowledge capabilities that allow us to test to extreme limits and complex standards.

We offer a wide array of EMC and EMI testing services:

Electrostatic discharge (ESD)

Electrostatic discharge (ESD) testing measures a device’s ability to tolerate discharge events. These events occur when a user touches the device and another metallic surface at the same time.

Harmonics and flicker

Harmonic frequencies greater than 50 Hz and voltage dips in the 5 to 15 Hz range can cause harmful interference for electronic devices. Devices need to be tested under these conditions to meet EMC compliance.

Electrical fast transients

Electrical fast transients testing (EFT) simulates a common type of real-world interference which was previously neglected. EFTs involve a high-frequency disturbance on a power line which occurs as a result of inductive loads being turned on or off.

Voltage dips and interrupts

Testing for voltage dips and interrupts (VDIs) involve simulating the conditions of voltage dips and voltage interruptions. The device is tested in the simulated environment to assess tolerance against VDIs.

Electrical surge

Surge testing is a key part of EMI analysis. NTS produces a low frequency, high energy electrical transient to simulate the effects of a lightning strike on a nearby power line. The device’s response is measured under these stringent conditions to test its tolerance against the surge.

Radiated susceptibility up to 200V/m, 10kHz to 40GHz

Military and Aerospace applications commonly require radiated susceptibility tests. NTS can perform radiated immunity testing up to 200V/m field strength in accordance with various military standards from 10kHz to 40GHz.

HIRF testing

High intensity radiated fields (HIRF) are divided into three frequency bands. HIRF-testing-frequenciesEach of these bands can affect airplane electronics in various ways:

  • Low frequency electromagnetic emissions between 10 kHz
    and 50 MHz
    — Low frequency HIRF use electrical parts like an antenna, carrying currents in the fuselage skin. These create little interior penetration.
  • High frequency electromagnetic emissions in the range of 100 MHz and 18/40 GHz — High frequency HIRF generates strong field penetration into the fuselage.
  • Medium frequency electromagnetic emissions between 30 MHz and 400 MHz — Medium frequency HIRF combine both LF and HF emissions effects. As a result, these emissions mimic both of the antenna-like performance as well as fuselage penetration.

HIRF certification generally involves measuring transfer functions to estimate the potential effects of EMI on an aircraft. NTS employs a variety of tools and techniques to produce accurate testing that is fully compliant with all required specifications.

NTS can help you meet requirements for HIRF certifications including RTCA/DO-160E/F, Boeing and Airbus requirements, and FAA HIRF Rule & Advisory Circular 20-158.

Lightning-multiple stroke, multiple burst and single stroke

NTS has lightning simulation capabilities that include:

  • Single Stroke
  • Multiple Stroke
  • Multiple Burst
  • DO-160 Section 15-22
  • Radiated Fields 200 +V/m
  • Electrostatic Discharge

We can precisely measure direct and indirect effects of a lightning strike. When it comes to direct effects, a lightning strike causes damage due to temperatures exceeding 20,000°C and electric spikes of more than 250,000 amperes. To simulate these conditions, NTS facilities have a series of high current generators and an indoor test area that measures 40 x 120 feet.

A lightning strike can also create a temporary rise in earth voltages after an impact. This indirect effect creates an intense electromagnetic field that can harm equipment up to a radius of one kilometer. NTS can run a variety of tests, including pin injections, transformer injections, and field immersions to determine the indirect effects of lightning. Together, these tests allow our engineering team to perform a thorough field and transient analysis. This further allows us to assess the indirect effects of a strike on everything from individual circuit parts to complex interconnected electronic systems.

MIL-STD-461 Testing

The MIL-STD-461 is a standard of the Department of Defense (DoD) that describes how to test equipment for electromagnetic compatibility. Even if this standard isn’t required, a device complying with this relatively strict standard will comply with most other common standards.

NTS can also help you with additional tests:

  • Magnetic susceptibility dc to 10kHz
  • Full CE immunity
  • Mode tuned chamber

EMC/EMI Engineering Services

Besides specific testing, NTS has the know-how to consult you on various engineering services related to EMC/EMI:

  • Electromagnetic environmental effects (E3) analyses of systems and platforms
  • EMC control plan
  • Independent EMI/EMC reviews
  • NARTE-certified engineers
  • Performance requirements definition and flow down
  • Requirements gap analysis
  • Risk mitigation plans
  • System EMC design
  • Test procedures and corrective action

Contact NTS for EMC Solutions

NTS testing labs can provide comprehensive HIRF and other electromagnetic interference testing for today’s most demanding clients and standards. NTS is the nation’s largest independent product testing and standards compliance organization. We regularly service the needs of military contractors, avionics manufacturers and more.

contact-nts-pullquote

NTS is renowned globally as an industry leader in providing EMC and EMI engineering and compliance services. Our experienced program managers and veteran engineers work closely with you to meet your EMC pre-compliance needs from conception, design and development to final test and production. We have expertise in various EMC/EMI engineering services to perform a variety of tests to meet standards across multiple industries and geographies.

With more than 50 years of experience, NTS has a long list of satisfied clients in our portfolio. Clients include organizations like Boeing, Cisco, U.S. Department of Defense, EMC, General Electric, Hewlett-Packard, Lockheed Martin, Microsoft, Motorola, Sony, Pratt & Whitney Rocketdyne, Texas Instruments and Tyco Electronics Corp. Contact us today to learn how we can help your business.

Using Programmable Logic Controllers for Test Automation and Process Control

Programmable Logic Controllers, or PLC’s, are basically a small computer with usable inputs and outputs. A PLC can be used to replace a set of relays, both time delay and regular, using counters and timers with input filtering and control. They typically run on ladder line programming (developed to let engineers and technicians use them without extensive programming knowledge) along with a graphic interface for ease of use.

Salt fog ControlThe real advantage of a PLC is flexibility and reliability. NTS Tempe is able to incorporate all of our customer requirements into one unit via a control point on a laptop and make changes on the fly.

The NTS PLC is composed of an OMRON ZEN microcontroller on an open board with solid state relays and terminal strips. The OMRON PLC has up to 6 transistor outputs good to 32VDC 10A, more than enough to either control things directly or drive an SSR (solid-state relay). It has up to 12 inputs 0-32VDC on the base unit that can be either positive or negative, and doubled with expansion units.

In one scenario, our team needed to control a hydraulic cylinder to preload the test item, start vibration for a set amount of time/number of cycles, then release the preload and repeat a specific number of times. In this instance, the PLC controlled the timing of an analog signal directly to the shaker amplifier and provided step signal attenuation on startup to avoid excessive shocks to the test unit from the shaker. A hydraulic cylinder was driven through an SSR and hydraulic valve.

The goal was to preload the unit to a specified amount measured with a load cell. We simply adjusted the pressure with a precision hydraulic regulator to get the required force. The shaker was then started and ramped up to the required levels, measured again with a load cell, held for a set time, then ramped down and stopped. We then depressurized the hydraulic cylinder and unloaded the test unit. After things had settled down, this sequence was repeated a few hundred times keeping a count of actual cycles. Using the PLC made all of this relatively easy.

In another instance a PLC was used to replace the entire control system in a liquid to liquid thermal shock machine. It controlled the movement of test items from hot to cold and back and monitored sensors indicating when test items were all the way into a tank or one of the drip positions ensuring that nothing was get out of sequence.

For ease of setup, external solid state timers set tank hold and drip periods driving the appropriate inputs of the PLC. A Watlow F4 controlled tank temperatures. In event of an error, the PLC would stop the test and initiate removal of a test item from the tank, then hold it in a neutral position.

SaltFog ChamberA final example has the PLC controlling all functions in a large salt fog chamber equipped with sulfur dioxide gas. It monitors salt and fresh water levels and fills the tanks from reservoirs as necessary. It also controls air flow to the salt fog towers ensuring air and SO2 are shut off during the fresh water bubbler fill. The PLC also acts as an interface between the Watlow F4 that controls temperature and SO2 cycles and the rest of the chamber. This allows the low level signal from the F4 to also control the system and shuts off the SO2 flow if the temperature goes out of tolerance, the salt fog chamber experiences an interruption or alarm.

NTS Tempe has seen much success using PLCs instead of conventional relays and timers. We recommend that if you have an older piece of equipment to update or need a custom setup, you consider using a PLC instead of traditional equipment. It gives a degree of flexibility along with control and safety that is sometimes difficult to obtain.

If you have any questions regarding the test cases in this article or would like to know how NTS Tempe engineers can apply their expertise to get your product qualified, please call the lab directly at 480.966.5517 or email our technical specialist Harold.Sibert@nts.com

Solar Testing Explained: MIL-STD-810 and Commercial

Solar 1

The first question a customer always asks is: “Why should I do solar testing and which test should I use?”

The answer to the first part is relatively simple. You should perform solar testing if your product will be exposed to sunlight. This could be in front of a window located indoors, beneath a transparent canopy, or permanently stationed outside. The second part of the question gets a bit more complicated. There are several different types of solar testing. It can incorporate halogen, full spectrum or UV only lamps and can include temperature, humidity and water spray.

First let’s focus on MIL-STD-810. It and other compliance standards require solar testing as part of product acceptance in which two different types of testing can be performed: Procedure 1 and Procedure 2.

Procedure 1 is primarily a heating effect test and is usually preformed with halogen lamps following a diurnal cycle profile. The purpose is to determine the highest maximum temperature the test unit will reach with repeated cycles in a controlled environment. The lamp intensity is varied from 0 W/m2 to 1120 W/m2 over a 24 hour cycle with the lamps and chamber temperature following a profile that simulates a natural day/night cycle.

Procedure 1 will reveal temperature related issues with the test unit and establishes the target test unit temperature for Procedure 2. This test can run 3 to 7 days in length with the equipment under test either powered on not. The airflow across the test articles is controlled to be the equivalent of a light breeze (300 to 600 feet per minute). MIL-STD-810 requires 3 days of stable and equal unit/chamber temperatures out of 7 days of testing. Full spectrum lamps can be used, but the difficulties controlling the intensity of full spectrum arc discharge lamps can sometimes be cost prohibitive.

Procedure 2 is a combination actinic and heating effects test using full spectrum lamps. The solar aging properties combined with heating effects can degrade items such as LCD or LED displays as well as coatings and seals causing deterioration, fading and discoloration. The lamp intensity is fixed at 1120 W/m2 by varying the distance of the test unit to lamps and the cycle normally runs in one of two variants. The first is 20 hours on and 4 off and the second is with the lamps continuously on. The purpose of the on and off lamp cycle is to expose issues related to rapid temperature changes caused by solar loading while continuous exposure will find the maximum actinic effects.

MIL-STD-810 calls for 20 hours on 4 hours off with exposure durations of 10 to 56 days or longer. Normally 10 days would be used for units that are primarily inside with some outdoor exposure while 56 day or longer would be for articles left outside such as transparent armor. With the 20 hour lights on cycle, solar aging is 2.5 times normal solar exposure. 10 days are the equivalent of 25 days outside in the sun and 56 days will be equivalent to 140.

It is important to note that Procedure 2 uses the maximum part temperature established in Procedure 1 as the target part temperature and the airflow across the test unit is controlled to maintain target temperature with the lights on. If Procedure 2 testing is to be performed, Procedure 1 should be run first to establish the maximum temperature.

Most commercial standards like ASTM or ANSI use similar lamp intensities and color spectrum as MIL-STD-810 (simulations with varying exposure times and environmental conditions), however some tests require a different type of simulator entirely.

One example would be fluorescent UVA or UVB lamps with a combination of temperature, humidity and water spray. This type of testing is usually performed on small samples and can run anywhere from 3 days to several hundred days. A specification such as this is written around a specific type of tester, one of which is a QUV environmental simulator. They do not incorporate significant heating effects and are mostly actinic UV and weathering tests.

Lastly, a common type of solar testing is performed on solar panels using lamps that provide high levels of UV and white light but little infrared and heating effects. This is typically done to establish power output and life cycle stability.

NTS Tempe performs fully accredited MIL-STD-810 Procedure 1 and Procedure 2 testing along with UV testing using a QUV environmental test unit. Our specialty is customizing solar testing to meet special customer requirements. For more information on how we can help qualify your products please call the lab directly at 480.966.5517 or email our technical specialist Harold.Sibert@nts.com

Why do I need EMC Compliance?

EMC TestingThere are a variety of reasons why your electrical/electronic products may be required to go through the Electromagnetic Compatibility (EMC) compliance process.

Regulatory Requirements

Most industrialized nations have established agencies or other regulatory bodies responsible for defining and enforcing EMC standards. If EMC regulations exist in a country, equipment manufacturers cannot legally ship their product into that country until compliance with those regulations is met. Professional compliance laboratories like NTS understand the global compliance process and possess the accreditations and capabilities needed to perform testing and certification to meet the relevant standards in all of your target markets.

Customer Requirements

There are many situations in which your customer may dictate EMC requirements. For example, if your customer is an RBOC (Regional Bell Operating Company), an extensive set of tests referred to collectively as Bellcore, are required before the RBOC will purchase your product. If your product or component will be included in a third-party product, your OEM customer will need proof that your product or component will meet appropriate regulatory standards. Your OEM customer will dictate the amount of testing and documentation they require. It is not unusual for an OEM customer to ask for compliance exceeding legal requirements.

Reliability/Performance

In some cases, you may want to self-impose reliability standards for your products; for example, if you only plan to ship your product in the United States, unlike in Europe, you are not required to pass immunity standards. However, you may want to establish your own immunity standards to ensure customer satisfaction by minimizing field failures.

How do I achieve EMC compliance?

Determining Relevant Standards

The first step in the compliance process is to determine the list of target markets where you plan to market and sell your products. Compliance regulations vary from country to country, so an investigation of current standards is required for each market where you intend to operate. Countries such as India have no formal Electromagnetic (EMC) requirements, whereas Taiwan has a very strict submission policy.

Self-Certification

Over the past several years, regulatory agencies around the world have been moving away from agency submittal applications because they are slow and inefficient. Most government agencies now allow for self-testing and self-certification. This means that you can simply affix a CE or FCC mark to your product and begin shipping without gaining government regulatory approval first.

However, self-testing and self-certification does not relieve your company from meeting the standards implied by the mark you place on your product. In fact, if you place a mark on your product when it doesn’t comply, it could result in serious consequences.

NTS has the formal accreditations to provide both the testing and the reports you need to meet a wide range of regulatory self-declaration requirements. We also create the reports that you must keep on file should an issue arise requiring proof of compliance.

Third party Verification

This is the process of having an independent party validate a product’s compliance. Third party verification adds significant credibility to a product’s test/compliance program, either for marketing or regulatory purposes.

Formal Certification

With certain types of products and in certain countries, a formal certification process may be required. For example, in Taiwan, a formal submission and approval is required, whereas the European Union might allow self-certification. In the USA a formal FCC submission, called a Certification, is required for any products designed to transmit radio signals. In addition to the testing costs to meet the relevant standards, you should also expect to pay agency submittal fees ranging from a few hundred to a few thousand dollars depending on the country and the type of product.

Understanding Testing in a Reverberation Chamber

REVERB

A reverberation chamber (mode tuned/mode stirred chamber) is a shielded enclosure or resonant cavity for RF testing which is statistically isotropic, random polarity, having RF uniformity within specified limits. Typically it has a paddle (or tuner) which stirs up the field, randomizing the boundary conditions. Mode tuned is where the paddle is stepped to a position and then RF is applied for a dwell time sufficient to exercise the equipment. Mode stirred is when the paddle is continually turned with RF energy applied for a full paddle revolution. Reverb chambers are useful for radiated susceptibility, radiated emissions (total radiated power), shielding effectiveness, and many other troubleshooting scenarios.

The benefits to reverberation testing are numerous. RF is applied to all exposed sides of the device under test (DUT) during a full 360° turn of the paddle, instead of a single side. For direct illumination testing, many standards require the all apertures of the DUT to be illuminated. On complex items this can be difficult – even impossible. Window effects testing, required when applying direct illumination, is not required during reverb testing because the field intensities are constantly changing. SAE ARP 5583 states that the reverb is the recommended and preferred method to show compliance for large and/or complex Level A (flight critical) systems. Test repeatability is much easier to obtain in a reverb chamber with proper processes, and running the test is much less complex than a single aspect angle test. Antenna distance, aim (focus), 3 dB beam width, location of the field probe, EUT layout, and location of the EUT in the working volume are all less of a factor in the repeatability of test.

REVERB2You should know if reverberation testing is right for your program. Reverb chambers are random in polarity which makes it challenging in determining directivity of RF energy. Testing multiple field levels on a system, such as outside the pressure vessel level and inside the pressure vessel level, can be difficult; all equipment in the chamber it is exposed to the same field. There are limitations on pulse width due to a high Q (efficient) chamber having large amount of stored energy. If you have small, simple equipment, single aspect angle tests may be faster and sufficient for test coverage. There are ways to compensate for each, and we can help with suggestions or assist in creating a test plan.

Both direct illumination and reverberation test methods are acceptable paths to certification. They both have benefits and drawbacks that champion each as a test method. Fortunately, NTS Rockford has the ability to test in both methods and the engineering expertise to support your path to certification. Should your project require this type of testing don’t hesitate to contact the lab directly at (815) 315-9250 and speak to one of our engineers!