NTS News Center

Latest News in Testing, Inspection and Certification

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

Environmental Testing Coming to Colorado!

NTS is pleased to announce that our Longmont, Colorado facility is now offering environmental testing starting in September, 2016. In addition to our current world-class EMI capabilities we can now provide:

DynamicsNTS Longmont Ling 335 shaker

  • Electro Dynamic Shakers:
    Sine, Random, Classical Shock
  • Shock Testing:
    Aircraft, Transportation, Bump
  • Constant Acceleration, Crash Safety

Environmental/ClimaticChamber 59 w car

  • Thermal Cycling
  • Temperature/Humidity
  • Temperature Shock
  • Temperature/Altitude

Whether you need to qualify for MIL-STD 810, MIL-STD 167, MIL-STD 1540 or RTCA DO-160, we can answer any questions you might have. When you are ready, our team can provide a competitively priced testing proposal and scheduling to fit your needs.

Click here to learn more about the NTS Longmont expanded capabilities.

Solar Radiation Testing in Accordance with Method 505 of MIL-STD-810

MIL-STD-810 Procedure 2 Solar TestingSolar radiation (sunshine) testing is one of the basic tests required for any military equipment planned to be deployed in the open and therefore subject to direct radiation from the solar source. The effects of this radiant energy can generally be divided into two groups or classes, heat effects and photochemical effects. Heat effects on exposed equipment can raise the internal temperatures of the equipment substantially above the ambient air temperature. Temperatures in excess of 160oF have been recorded in parked aircraft exposed to the sun while ambient air temperature was in the 90oF range. Photochemical effects of sunlight may hasten the fading of colors and lead to the deterioration of plastics, paints, rubber and fabrics. The combined effects may lead to the outgassing of plasticizers in some materials along with discoloration and a reduction in transparency.

MIL-STD-810, Method 505.5 outlines two procedures for performing the Solar Radiation test. Procedure I requires a cyclic exposure based on the diurnal cycle and is most useful for determining heating effects on exposed materiel as well as materiel enclosed within a container. Procedure II is a steady state (non-cyclic) exposure most useful for evaluating actinic (photochemical) effects of ultraviolet radiation on materiel since it represents an accelerated test with a factor of 2.5. Because Procedure I is more akin to a natural cycle and does not have the acceleration factor of Procedure II, it is not an efficient cycle with which to evaluate long term exposures. Therefore, when it is used mainly to evaluate the direct heating effect, Procedure I can be performed with source lamp arrays emitting less than the full solar spectrum. Procedure II however, demands full spectrum sources emitting light in the ultraviolet range if the total effects of long term exposure are to be properly evaluated.

The solar light spectrum has been accurately measured over the wavelength range of 280 – 3000 nm as well as the power distribution within this range, and it is this range that we would seek to reproduce in the Solar Radiation test.  Reproducing this entire range using lamp sources however can be quite challenging. Sources emitting ultraviolet wavelengths between 280 and 400 nm tend to be quite costly and their performance deteriorates quickly. Some of the MIL-STD recommended sources such as xenon arc and carbon arc fall into this category.  In fact, it was reported that the first commissioned sunshine test facility in 1945 fell short of the contract requirements due to several deficiencies, one of which was the amount of UV that could be produced at the test item. Cost and reliability issues are why many test labs have chosen to perform only Procedure I  with source lamps covering the visible and infrared spectrum range of 400 – 3000 nm (0.4 – 3.0 µm).

Reproduction of the required environment for the Solar Radiation test requires a chamber space in which the ambient air temperature and airflow over the test item can be controlled as well as a solar light source which may consist of a single source in the case of arc-type lamps or a multiple source array in the case of metal halide or incandescent type lamps. The distance of the light source from the test item may be varied to achieve the required irradiance. Airflow over the test item can significantly impact test results. When MIL-STD-810D introduced the “cycling for heat effects” (Procedure I) the guidance for airflow was to use airflow as low as possible consistent with achieving satisfactory control of the ambient air temperature at the test item or between 0.25 and 1.5 m/s (50 to 300 ft/min). The current guidance from MIL-STD-810G has changed for procedure I to 1.5 to 3.0 m/s (300 to 600 ft/min) in recognition of better field data. The requirement for peak radiation intensity at 1120 W/m2 has changed little over the history of the Solar Radiation test although there have been slight changes to the spectral energy distribution based on updated measurement techniques of the actual solar source.

When the primary concern is testing for heat effects, the question is often asked why an oven or chamber test for enclosed equipment could not be used in place of the Solar Radiation test.  The primary reason is that ovens and chambers transfer heat from a uniform ambient atmosphere surrounding the test item, whereas the solar test transfers heat through direct radiation. The directional effect of radiant heating produces temperature gradients through the test item that are not replicated in ovens or temperature chambers.

When a Solar Radiation test is required,

  • Perform the Solar Radiation test prior to the High Temperature test, as the product temperature measured in the solar chamber may need to be used as the ultimate high operating temperature for the product.
  • Consider the orientation of the test item within the solar chamber so as to replicate the in-use conditions with respect to both the direct radiant light energy and the airflow direction. This will affect both the temperature gradients and any cooling effects provided by the airflow.
  • When testing to Procedure I, remember that several consecutive cycles will likely be required for the product to achieve the ultimate high operating temperature for the most critical area of the test item to be within 2oC of the previous cycle. This usually means 3 to 7 cycles.
  • If operation of the test item is required, operational times will need to coincide with the peak response temperature of the test item in each cycle which will not coincide with the peak radiation intensity.

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.

Q & A: What is the correct order for Sand, Dust, and Salt Fog in MIL-STD-810

Blowing Sand and Dust Test

Blowing Sand and Dust Chamber for MIL-STD-810, MIL-STD-202 and RTCA DO-160

Question: I have a military customer who requires Blowing Sand, Blowing Dust, and Salt Fog tests according to MIL-STD-810. However, my customer did not specify which test should be performed first. Is there a specific order in which these tests should be performed? Does it matter?

NTS Answer: Although not necessarily clear in previous revisions, guidance was added to Method 509 starting with the F revision of MIL-STD-810:

Although generally inappropriate, if sand and dust testing is required on the same test item, perform it following salt fog testing.

This is due to the fact that the sand and dust tests can produce severe abrasion of a test item. This is particularly true for the surface treatments often applied to the exterior surfaces of items in order to reduce or eliminate the possibility of corrosion. Paint, anodizing, iridite, and other surface preparations can all be adversely compromised by the sand and dust tests so that the test item could easily show corrosive effects if subsequently subjected to the salt fog test.
Additional guidance was also added to method 510 (Sand & Dust):

If both sand and dust procedures are to be applied to the same test item, it is generally more appropriate to conduct the less damaging first, i.e., blowing dust and then blowing sand.

Therefore, the most appropriate sequence for the three tests in question would be:
1. Salt Fog
2. Blowing Dust
3. Blowing Sand

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