Mil-Std-810G – Part 8 (Rain)

This is part 8 of a series delving into the intricacies of Mil-Std-810G.

 

810G covers rain exposure in Method 506.5. This method comprises 11 pages. The purpose of Method 506.5 is to help determine effects of rain, water spray or dripping water:

•  The effectiveness of protective covers, cases, and seals in preventing the penetration of water into the materiel.


• The capability of the materiel to satisfy its performance requirements during and after exposure to water.


• Any physical deterioration of the materiel caused by the rain.


• The effectiveness of any water removal system.


• The effectiveness of protection offered to a packaged materiel.

 

Method 512.5 covers immersion and is considered a more stringent test than 506.5. If the material configuration is the same as when tested for 512.5, 506.5 testing is redundant.

 

Limitations to this section include:

• The method is not intended to examine rain erosion effects such as radomes, helicopter blade leading edges, etc.


• It may be difficult to determine rain effects on electromagnetic radiation and propagation because of the size of the required facility.


• Determining adequacy of aircraft windshield rain removal.


• Does not address pressure washers or decontamination devices.


• Effects of extended periods of exposure to rain or light condensation drip rates caused by an overhead surface with pooling water.

 

Method 506.5 provides three procedures:

• Procedure I – Rain and blowing rain. Applicable to material that will be deployed out-of-doors.


• Procedure II – Exaggerated. For use for large objects that may not fit in a chamber. Uses water spray under pressure from a nozzle.


• Procedure III – Drip. Appropriate when material is normally protected from rain but may be exposed to falling water from upper surfaces.

 

As with all of Mil-Std-810G, the test methods are intended to simulate real world conditions. For example, it may be advantageous to start the test with the tested item warmer (10°C) than the “rain”. The “rain” will cause a lower temperature and subsequent lower pressure within the tested equipment which may draw in water revealing a possible failure point.

 

While rainfall rates around the world vary, and it may be appropriate to mimic those higher rates, in general, a rate of 4 in/hr is not an uncommon occurrence and will provide a reasonable degree of confidence.

 

Wind is also a factor and provision should be made to provide a simulated velocity of at least 40mph. Higher velocities may be appropriate depending on the intended environment. The item under test should be oriented to maximize potential rain penetration.

 

For Procedure I (rain and blowing rain), the test duration should be at least 30 minutes per surface. Rotate the item under test for each surface to be exposed to the wind.

 

Chassis Plans has engineered and produced rugged enclosures for exterior environments.

 

By David Lippincott Chassis Plans www.chassis-plans.com

Mil-Std-810G – Part 8 (Rain)

Mil-Std-810G – Part 7 (Solar Radiation - Sunshine)

This is part 7 of a series delving into the intricacies of Mil-Std-810G.

 

810G covers Solar Radiation in 505.5 and serves two purposes:

1. To determine heating effects from sunshine impinging directly on equipment (Procedure I).


2. To help identify material degradation from sunshine (Procedure II).

 

Mil-Std-810G, Method 505.5, is a rather complicated section at 15 pages with three Annexes (A – Detailed Guidance on Solar Radiation Testing), (B – Instrumentation Installation, Placement and Guidance), (C – Guidance on Tables and Figures) at 15 additional pages combined.

 

Of primary concern to users of computers, the heating effects of solar radiation are more important than material degradation.  Computers are generally manufactured with metal enclosures.  On the other hand, LCDs may suffer from both heating effects and material degradation.  Coatings may degrade somewhat with color changes but the impact of plastic becoming brittle, for example, does not apply to a computer.  A computer painted black sitting outside will become very hot with the subsequent impact on keeping the internal components within operating temperature specifications.

 

The maximum surface and internal temperatures attained by materiel will depend on:

 

• the temperature of the ambient air.


• the intensity of radiation.


• the air velocity.


• the duration of exposure.


• the  thermal  properties  of  the  materiel  itself,  e.g.,  surface  reflectance,  size  and  shape,  thermal conductance, and specific heat.

 

Materiel can attain temperatures in excess of 60°C if fully exposed to solar radiation in an ambient temperature as low as 35 to 40°C.  Paint color and composition can have a major impact on surface temperature.

 

810G Method 501.5 (High Temperature) mentions Method 505.5 as a factor to consider (Aggravated solar) when determining effects of high temperature.  In addition, Method 503.5 (Temperature Shock) also references 505.5 in section 2.3.1 for ‘Climatic Conditions’.

 

As you can imagine, 505.5 specifies “Use this Method to evaluate material likely to be exposed to solar radiation during its life cycle in the open in hot climates”.

 

The impact of solar radiation heating effects include:

 

• Jamming or loosening of moving parts.


• Weakening of solder joints and glued parts.


• Changes in strength and elasticity.


• Loss of calibration or malfunction of linkage devices.


• Loss of seal integrity.


• Changes in electrical or electronic components.


• Premature actuation of electrical contacts.


• Changes in characteristics of elastomers and polymers.


• Blistering, peeling, and de-lamination of paints, composites, and surface laminates applied with adhesives such as radar absorbent material (RAM).


• Softening of potting compounds.


• Pressure variations.


• Sweating of composite materials and explosives.


• Difficulty in handling.

 

Material effects of solar radiation, primarily from UV exposure, include:

 

• Fading of fabric and plastic color.


• Checking, chalking, and fading of paints.


• Deterioration of natural and synthetic elastomers and polymers through photochemical reactions initiated by shorter wavelength radiation. (High strength polymers such as Kevlar are noticeably affected by the visible spectrum. Deterioration and loss of strength can be driven by breakage of high-order bonds (such as pi and sigma bonds existing in carbon chain polymers) by radiation exposure.)

 

Testing is performed in a chamber with a bank of full-spectrum lamps mimicking the sun’s light and heat output.  A maximum irradiance intensity of 1120W/m² is provided and uniform across the top surface within 10 percent of the desired value.  The Method outlines several scenarios for lamp selection and operation to give the desired results.

 

The ability to vary the lamp output to mimic diurnal variation in solar radiation should be provided for non-static testing.  Where only thermal effects are considered, infrared lamps may be used but realize that coatings and filters on the test item may respond differently to those wavelengths versus sunlight.  As a side note, infrared account for 42.1% (471.5 W/m²) of the sun’s total irradiance

 

For Procedure I (temperature), for worldwide deployment, a peak chamber temperature of 120° F is provided along with airflow of 300 to 600 ft/min to mimic naturally occurring winds.  Generally, an airflow of as little as 200 ft/min can cause a reduction in temperature rise of over 20 percent as compared to still air.  If the item is shielded from the wind in the operating environment, then no airflow would be provided during test.  Maintaining the proper chamber temperature can be challenging as the lamps themselves will generate considerable heat and the unit under test will also be warming the air.  Thus, cooling the chamber may be more problematic versus heating it.

 

Humidity is generally not a concern unless the material under test is known to be sensitive to moisture.

 

The test item should be clean while being tested.  That being said, in many parts of the world, dust and dirt are prevalent and should be considered when planning the testing.  Dust and other surface contamination may significantly change the absorption characteristics of irradiated surfaces.

 

Testing for thermal effects should be performed with the test item in a mode that generates the most heat.

 

Spectral distribution changes with the anticipated operational altitude.  There is more damaging UV radiation at higher altitudes which should be considered.  For example, a long duration high altitude UAV manufactured with composite wings would be tested for that environment looking for material degradation in the wings which may cause structure failure.

 

As with other 810G Methods, Method 505.5 is a general outline and it is left to the end user to create a test plan to align the test with the anticipated environment.  An item in the middle of an asphalt parking lot in Phoenix would be tested differently than an item on a car dash in Anchorage.  The tests should replicate the intended environment.

 

The tests can be performed mimicking the diurnal cycle (24 hours with variable lamp output and variable chamber temperature) or can be steady state (20 hours with the lamps on and 4 hours off).  Repeat the cycle the number of times outlined in the test plan.

 

Chassis Plans has engineered rugged industrial computers for deployment in exposed locations in high-temperature environments and can assist with your project.

 

by David Lippincott Chassis Plans www.chassis-plans.com

Mil-Std-810G – Part 7 (Solar Radiation - Sunshine)

Mil-Std-810G – Part 6 (Contamination by Fluids)

This is part 6 of a series delving into the intricacies of Mil-Std-810G.

 

810G covers contamination by fluids in 504.1.  Use the contamination by fluids tests to determine if equipment is affected by temporary exposure to contaminating fluids such as may be encountered during its life cycle.  In the case of rugged computers in the military environment, these fluids can include:

• Water and salt water


• Jet fuel (kerosene)


• Gasoline


• Diesel fuel


• Hydraulic fluids


• Lubricating oils


• Solvents and cleaning fluids


• Deicing and antifreeze fluids


• Disinfectant


• Fire extinguishants.

 

Fluids can be intentionally applied in the normal course of operation such as cleaning fluids or there may be inadvertent exposure such as splashing, spillage, or fluids on hands or gloves.

 

The effects of such fluids can include:

• Dissolving or softening paint on the equipment


• Damaging plastic parts


• Conductive effects


• Insulation effects such as leaking across switch contacts


• Gumming up the works such as a full-travel keyboard


• Binding or slackening of moving parts


• Differential contraction or expansion rates or induced strain rates of dissimilar materials


• Changes in electrical and electronic components


• Electronic or mechanical failures due to rapid water or frost formation.


• Excessive static electricity


• Interruption of electrical continuity (such as “grounding” fingers on EMI strips)


• Increase in electrical resistance due to thermo-mechanical “fretting corrosion”

 

In general, it is best to test material samples instead of the entire product.  Painted samples can be used to test impact on the paint or powder coating.  Individual components such as switches and drive carriers can be easily tested.

 

It should be noted that testing for contamination by fluids should be done after other tests for 810G as contamination by the fluids may potentially damage test equipment required for other tests.

 

The tests are not intended to demonstrate suitability of materials in continuous contact with a fluid such as a pump, nor should it be used to demonstrate resistance to electrolytic corrosion.

 

810G includes consideration of temperature effects of exposure to fluids and the operating environment should be evaluated in preparing for the tests.  Many chemicals are much more reactive at higher temperatures and may not have any impact at lower temperatures.

 

Sections of 504.1 include for testing:

• Length of exposure


• Test fluids


• Combination of test fluids


• Test Temperature


• Test item temperature


• Test fluid temperature


• Soak temperature


• Fluid exposure duration


• Methods of application

 

The goal of the testing is to analyze any contamination effects for their immediate or potential (long-term) effects on the proper functioning of the test item or safety during its life cycle.

Mil-Std-810G – Part 6 (Contamination by Fluids)

Mil-Std-810G - Part 5 (Temperature Shock)

This is Part 5 of a series delving into the intricacies of Mil-Std-810G.

 

810G covers temperature in 501.5 (High Temperature) and 502.5 (Low Temperature), both of which have been covered in previous blogs.  In addition, 503.5 covers Temperature Shock. Method 520.3 details testing which combines temperature, humidity, vibration and altitude interactively.  Methods 520.3 will be examined in future blogs.  Method 503.5 covers 13 pages of Mil-Std-810G.

 

Use the temperature shock test of 503.5 to determine if materiel can withstand sudden changes in the temperature of the surrounding atmosphere without experiencing physical damage or deterioration in performance.

 

Temperature shock effects on computers and LCDs include:

• Shattering of plastic materials


• Binding of moving parts


• Drive failure


• Cracking from differential expansion (contraction) of dissimilar materials


• Integrated Circuit (IC) bond failure


• Cracking of LCD cover glass materials


• Delamination of the LCD display


• Electronic or mechanical failures due to rapid water or frost formation

 

Method 203.5 includes one test procedure with four variations – essentially in the length of the test and the shock itself. It employs constant temperature at each of the extreme shock conditions because, in many instances, the thermal shock itself so outweighs the other thermal effects that the test may be performed using two constant temperatures. This is particularly the case when more severe shocks are desired, such as for evaluation of safety or initial design, and when extreme values will be used.

 

The tests simulate what happens when you would move equipment from one environment rapidly into a much different environment.  That can be from hot to cold or from cold to hot.  For hot to cold, picture moving from a warm control room to outside in the artic where the temperature might be -30 deg C or lower.  Cold to hot can be as simple as moving from a cool air conditioned room to outside in Texas in the middle of summer where the temperature and humidity are both very high causing immediate condensation on the cold equipment.

 

As with other 810G methodologies, there are no absolute values associated with the different tests.  The tests are designed to simulate performance in an intended environment.  Thus, determining the climatic conditions where the equipment is to be deployed or stored is the first step.  Then the test high and low points can be determined.  503.5 actually recommends using a range of temperatures that reflects the anticipated in-service environment, rather than some arbitrary extreme range.

 

The four test variations are:

• Procedure I-A One-way shock(s) from constant extreme temperature.  Appropriate for material that is likely to be exposed only rarely to thermal shock in one direction, perform at least one shock for each appropriate condition, i.e., low to high temperature, or vice-versa.


• Procedure I-B Single cycle shock from constant extreme temperature. For materiel that is likely to be exposed to only one thermal shock cycle (one in each direction), perform one shock for each appropriate condition, i.e., low-to-high temperature, and one in the opposite direction


• Procedure I-C Multi-cycle shocks from constant extreme temperature. Appropriate for systems that may be subjected to multiple temperature shock events.  A minimum of three shocks is specified.


• Procedure I-D Shocks to or from controlled ambient temperature. Essentially the same as I-C except the shock is to ambient instead of extreme hot and cold temperatures.

 

The tests should consider the deployed state of the equipment.  Perhaps the systems are mounted in transit cases which will slow the internal temperature changes.  On the other hand, a transit case may maintain an internal temperature which will suddenly change when the covers are removed.

 

The tests involving ambient require a single chamber.  Tests to extreme high and low temperatures require two chambers where the equipment is moved from one chamber to the other.  There is test equipment providing two side by side chambers with a divider between them allowing the equipment to be shuttled between the different temperatures automatically.

 

Chassis Plans has demonstrated experience working with customers to design rugged systems appropriate for any environment including rapid temperature changes.

Mil-Std-810G - Part 5 (Temperature Shock)

Mil-Std-810G - Part 4 (Low Temperature)

This is Part 4 of a series delving into the intricacies of Mil-Std-810G.

 

810G covers temperature in 501.5 (High Temperature) which was discussed in a previous blog, 502.5 (Low Temperature) and 503.5 (Temperature Shock). Method 520.3 details testing which combines temperature, humidity, vibration and altitude interactively.  Methods 520.3 will be examined in future blogs.  Method 502.5 covers 6 pages of Mil-Std-810G.

 

This method is not intended for testing materiel to be installed in and operated in unpressurized aircraft, since such materiel would usually be tested according to Method 520.3.

 

Low temperature effects on computers and LCDs include:

• Failure of the system to boot


• Drive failure


• Drive won’t spin due to internal frost


• Stiffening of shock mounting devices


• Change in vibration and shock dynamic response


• Cracking of surface coatings


• Cracking from differential expansion (contraction) of dissimilar materials


• Change in electrical properties of electronic components


• Integrated Circuit (IC) bond failure


• LCD will not operate due to sluggish or frozen liquid crystal material


• Delamination of the LCD display


• Excessive static electricity

 

As with Method 501.5 for High Temperature, with a few exceptions, the Methods for low temperature do not place absolute limits on the devices to be tested.  There is no specification delineating a minimum temperature of 0 deg C, for example.  Thus, a manufacturer stating their device has been tested per Mil-Std-810G for operation between 0 and 50 deg C has written their own test method.

 

The limitations for 502.5 specify the Method is appropriate for short term (months as opposed to years), even distributions of cold throughout the test item.  For the purposes of testing, time is allowed for the test item to stabilize in temperature.

 

Within 502.5 are three procedures:

• Procedure I – Storage


• Procedure II – Operation


• Procedure III – Manipulation

 

In general, companies will publish both storage and operating temperature specifications but rarely, if ever, Manipulation for computers or LCDs.  Use Procedure III to investigate the ease with which the equipment can be set up and disassembled by personnel wearing heavy, cold-weather clothing.  In the case of computers, the use of gloves might be an impediment to operating the systems.

 

Testing for cold simulates conditions in selected regions or for worldwide use.  Note that Antarctica is excluded from consideration by international treaty restrictions for military equipment. On the other hand, testing for civilian use in Antarctica is appropriate.  Solar loading is not considered an issue so testing at constant temperatures is allowed.

 

There are three cold test environments:

 

Basic Cold covers most of Europe; Northern contiguous US; Coastal Canada; High-latitude coasts (e.g., southern coast of Alaska); High elevations in lower latitudes and ranges from -21 to -31 deg C for ambient air temperature and -25 to -33 deg C for induced environment (storage and transit).

 

Cold covers Canada, Alaska (excluding the interior); Greenland (excluding the “cold pole”); Northern Scandinavia; Northern Asia (some areas), High Elevations (Northern and Southern Hemispheres); Alps; Himalayas; Andes and ranges from -37 to -46 deg C for ambient and -25 to -33 deg C for induced environment (storage and transit).

 

Severe Cold covers the Interior of Alaska; Yukon (Canada); Interior of Northern Islands; Greenland ice cap; Northern Asia and specifies a single temperature of -51 deg C.

 

Note that there are frequencies of occurrence that certain low temperatures may be experienced.  For example, there is a 20 percent chance of going to -51 deg C and a 1 percent chance of going all the way down to -61 deg C.  For extended storage such as years in areas that experience extreme cold, there is a chance the material may experience temperatures approaching -65 deg C.

 

Testing time for storage of 4 hours at a stabilized temperature is generally considered adequate for nonhazardous or non-safety-related equipment.  Some items such as explosives may continue to degrade over time at low temperatures and should be tested further as appropriate.

 

Note that Method 502.5 does not mention humidity.  Because the humidity is so low, essentially non-existent at these low temperatures, static electric generation does become an issue and must be considered.  As a side note, it is much more important to practice safe static electric remediation procedures at low temperatures including use of wrist straps, grounding points, non-static generating packaging and wiping cloths, etc.  Users may have a Styrofoam coffee cup handy trying to keep warm and Styrofoam can generate very high static fields.

 

The test itself is rather anti-climatic.  The device under test is placed in a chamber, powered down, and the temperature lowered to the desired value.  Generally the rate of change in the chamber is limited to 3 deg C per minute to prevent thermal shock.  Soak at the storage temperature for 4 hours, then raise the chamber temperature to the operating temperature, let the item stabilize internally at that temperature, then power it on and check operation.

 

Chassis Plans is versed in low temperature operation of rugged military grade computers and LCDs and can provide remediation such as extended temperature components or heaters as required.  There are multiple options for products such as rugged LCDs to enable low temperature operation.

 

 

Mil-Std-810G - Part 4 (Low Temperature)

Mil-Std-810G - Part 3 (High Temperature)

This is Part 3 of a series delving into the intricacies of Mil-Std-810G.

 

810G covers temperature in 501.5 (High Temperature), 502.5 (Low Temperature) and 503.5 (Temperature Shock). Method 520.3 details testing which combines temperature, humidity, vibration and altitude interactively.  Methods 502.5 and 520.3 will be examined in future blogs.  Method 501.5 covers 12 pages of Mil-Std-810G.

 

High temperature effects on computers and LCDs include:

• Exceeding the published high temperature limits for the components such as processors and chip sets causing damage


• Exceeding operating limits on components inside the power supply such as transformers


• Intermittent operation as the processors automatically slows down in a protective mode


• Intermittent operation as power supply modules shut down in a protective mode


• Reduced component life


• The screen on LCDs can turn black at elevated temperatures


• Glue creep or failure

 

With a few exceptions, the Methods for temperature do not place absolute limits on the devices to be tested.  There is no specification delineating a maximum temperature of 50 deg C, for example.  Thus, a manufacturer stating their device has been tested per Mil-Std-810G for operation between 0 and 50 deg C has written their own test method.

 

The limitations for 501.5 specify the Method is appropriate for short term (months as opposed to years), even distributions of heat throughout the test item.  For the purposes of testing, time is allowed for the test item to stabilize in temperature.

 

Within 501.5 are three procedures:

• Procedure I – Storage


• Procedure II – Operation


• Procedure III – Tactical Standby to Operational

 

In general, companies will publish both storage and operating temperature specifications but rarely, if ever, tactical standby to operational for computers or LCDs. The term “tactical” is used to identify materiel that is not in storage, but is in a standby operational configuration, and as such is subjected to extended non-operational conditions immediately prior to operation.

 

Humidity is usually not a factor in high temperature testing.  However, climatic conditions should be considered. Identify the appropriate climatic conditions for the geographic areas in which the materiel will be operated and stored. There are two climatic categories where high temperatures are typically encountered: Hot Dry and Basic Hot.

 

Basic Hot is applicable to many parts of the world, extending outward from the hot dry category of the southwestern United States, northwestern Mexico, central and western Australia, Saharan Africa, South America, southern Spain, and southwest and south central Asia.  The ambient air temperature is specified at 30-43 deg C (86 to 110 deg F) and induced at 30-63 deg C (86 to 145 deg F).  Induced temperature is a result of heat loading from sun exposure, for example.  Humidity ranges from 5% at 63 deg C (induced) to 44% at 31 deg C (induced).    As can be seen, the target area is hot and dry!

 

Hot Dry covers Southwest and south central Asia, southwestern United States, Saharan Africa, central and western Australia, and northwestern Mexico.  The ambient temperature is specified at 32 to 49 deg C (90 to 120 deg F) and induced at 33 to 71 deg C (91 to 160 deg F).  Humidity ranges from 1% to 7%.  Really hot and really dry.

 

Cyclic temperature exposure should be considered.  Generally, 7 cycles is sufficient for Procedure I – Storage and 3 cycles for Procedure II – Operation.

 

A situation to be aware of and which needs careful attention and control is run-away chamber temperature during testing.  A high power computer may generate more heat than the chamber can cool resulting in unanticipated high temperatures beyond the scope of the testing.

 

Chassis Plans rugged military grade computers are designed to function in high temperature environments for high power systems.  Included are multiple high velocity fans, optimized air flow paths, and Chassis Plans’ proprietary SysCool®  Intelligent Fan Controller.

Mil-Std-810G - Part 3 (High Temperature)

Chassis Plans Offers 5 Year Warranty on All Server Products

SAN DIEGO, CA, August 1, 2015 — As part of its continuing drive to provide outstanding service and support to its customers, Chassis Plans is offering a 5 year warranty on its standard range of 1U to 5U Servers starting Aug 1, 2015. This will include all parts and labor and the cost of returning the refurbished and repaired server to the customer.

 

Mike McCormack, President of Chassis Plans stated “we are confident of the quality of the products we design and build in our factory in San Diego and want to provide an additional peace of mind to our customers that will assure them that they will always receive the most comprehensive service and support that our company can provide”.

 

For further information, visit the Chassis Plans website at www.chassis-plans.com, call 858-571-4330 or email saleseng@chassisplans.com.

 

Chassis Plans Offers 5 Year Warranty on All Server Products