Mil-Std-810G - Part 9 (Humidity)

This is part 9 of a series delving into the intricacies of Mil-Std-810G.

 

810G covers humidity in Method 507.5.  This method comprises 21 pages.

 

The purpose of Method 507.5 is to determine the resistance of material to the effects of a warm, humid environment.  It is applicable to material that is likely to be stored or deployed in areas in which high levels of humidity occur.   The essence of 507.5 is hot and humid.  Effects on electronics can include break down of insulators as they absorb moisture or condensation when a cold object is brought into contact with a warmer humid environment.

 

The method may not reproduce all the humidity effects associated with the natural environment nor is this method applicable to low humidity situations.

 

There is not specific method that addresses low humidity.  However, for completeness, low humidity exposure should be considered.  The usual side effect of low humidity is static electricity build-up and subsequent discharge causing spurious operation or material damage to sensitive electronic devices.  MIL-HDBK-263B is the reference for Electrostatic Discharge Control.

 

Warm, humid conditions can occur year-round in tropical areas, seasonally in mid-latitude areas and in material subject to changes in pressure, temperature, and relative humidity.  Material enclosed in non-operating vehicles can experience high internal temperature and humidity conditions.

 

Specifically, this method does not address:

• Condensation resulting from changes of pressure and temperature for airborne or ground materiel.


• Condensation resulting from black-body radiation (e.g., night sky effects).


• Synergistic effects of solar radiation, humidity, or condensation combined with biological and chemical contaminants.


• Liquid water trapped within materiel or packages and retained for significant periods.


• This method is not intended for evaluating the internal elements of a hermetically sealed assembly since such materiel is air-tight.

 

Method 520.3 should be considered in conjunction with Method 507.5 to explore the synergistic effects of temperature, humidity and altitude.

 

The effects of high humidity can include:

 

a. Surface effects, such as:

1. Oxidation and/or galvanic corrosion of metals.


2. Increased chemical reactions.


3. Chemical or electrochemical breakdown of organic and inorganic surface coatings.


4. Interaction of surface moisture with deposits from external sources to produce a corrosive film.


5. Changes in friction coefficients, resulting in binding or sticking.

 

b. Changes in material properties, such as:

1. Swelling of materials due to sorption effects.


2. Other changes in properties.
   
   (a) Loss of physical strength.
   
   (b) Electrical and thermal insulating characteristics.
   
   (c) De-lamination of composite materials.
   
   (d) Change in elasticity or plasticity.
   
   (e) Degradation of hygroscopic materials.
   
   (f) Degradation of explosives and propellants by absorption.
   
   (g) Degradation of optical element image transmission quality.
   
   (h) Degradation of lubricants.

 

c. Condensation and free water, such as:

1. Electrical short circuits.


2. Fogging of optical surfaces


3. Changes in thermal transfer characteristics.

 

In addition to “Natural”, Method 507.5 provides for two Procedures: Induced and Aggravated.  Natural simulates a natural environment.  Induced simulates a natural environment for storage and transit.  Aggravated exposes the test item to more extreme temperature and humidity levels than those found in nature but for shorter durations.  The Natural test criteria was selected to mimic Majuro, Marshall Islands with a temperature range of 88 to 105 degrees F. and relative humidity (RH) of 59% to 88% for the Hot Humid test.  Cycle B2 (High RH) provides for lower temperatures but RH up to 100%

 

The test duration is recommended to be a minimum of 45 cycles for non-hazardous materials to 180 days for Induced testing for hazardous material.  Hazardous materials are those in which a failure may cause damage to adjacent material or injury or death to a user.  The purpose of the higher cycle counts is to establish confidence in the testing.

Mil-Std-810G - Part 9 (Humidity)

Why go to a Virtual Desktop Infrastructure (VDI)?

Traditional desktop PCs are being replaced in many installations by new Thin/Zero Client Workstations and Data Center Servers running virtual instances of application software.  With the pervasiveness of Gigabit Ethernet the user experience using this technology has been vastly improved.  This has a number of benefits to the corporation in the form of:

 

1. Increased Security as the workstation clients are not running the application software directly, nor do they store the data itself.  The applications run on the server and the data is stored in managed mass storage. Only Keystrokes and screen refreshes are transmitted over the internal network.


2. Protection against cyber-attacks as the clients are connected to a managed internal network with central auditing, not directly to the Internet.


3. Decreased IT support as the software applications are standardized on the server so that all users are on the same version which also leads to increased collaboration on team projects.


4. The ability to block transfer of data from the data center to the client for offloading to a USB stick or other mass storage device.

 

Because of the increased security aspects of this technology, in light of recent data disclosures and cyber attacks, the Department of Defense is actively pursuing a program to replace virtually all their “fat” PC systems with Thin or Zero Clients.  The Air Force alone is planning on replacing 1.2 million PCs with thin clients in 2014.

 

Now, let’s examine the differences between Thin Clients and true Zero Clients.  Both are small form factor and are typically attached to the back of the display monitor, freeing up desk space.  They are also fairly simple to install, not requiring the massive task of loading all the allocation software during the initial installation.  They are also very low power (<10 Watts) and fan-less which provides for a more conducive work environment. There are a number of differences between the two and they are worth noting.

 

Thin Clients are end point devices with some type of skinny, locked down Operating System such as Linux or Windows Embedded and is typically stored in Flash Memory.  They use more traditional hardware such as CPU boards and Graphic cards and run such applications as browsers, e-mail clients and PDF viewers.  The application is rendered at the terminal and provides for user interaction with the program running on the server.  This makes it almost impossible to get a virus or other malware.  Thin clients are more flexible as they offer much more peripheral support since they are configurable and ideally suited for multi-protocol environments.

 

Zero clients do not have an Operating System, rather a specifically designed processor that runs a specific protocol.  The image is rendered on the host server and only the raw pixels and keystrokes are transmitted over the network.  This reduces the bandwidth required on the network as dedicated hardware Codecs on the host compress the pixel data before sending it to the client.  This offers exceptional video performance but is less flexible as it cannot support various protocols.  They also rarely require any software updates/patches and are completely immune to viruses.

 

In summary, this technology provides for a much more secure environment protecting the data and preventing attacks from viruses, malware and keystroke loggers as well as preventing data theft and corruption.  The first step on deciding between thin and zero clients really rests in the requirements of the network and the connection you prefer with your end uses.

 

Chassis Plans can provide ruggedized Thin/Zero Clients for use in harsh environments.

 

By Erica Sullivan Chassis Plans www.chassis-plans.com

Why go to a Virtual Desktop Infrastructure (VDI)?

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)

Test Post from Chassis Plans Rackmount Computer Blog

Test Post from Chassis Plans Rackmount Computer Blog http://www.chassis-plans.com/blog