Riding the Rails is Rough

Railroads offer a multitude of possible applications for rugged industrial computer systems. The railroad environment can also be amongst the harshest possible environments for computers. There can be extremes of both high and low temperatures, high and low humidity, high dust and dirt loading in the air, and continuous vibrations. In some cases, these conditions can be improved but not always or it may not be economical to do so.

 

Applications include both fixed environment and rolling stock.

 

Fixed or station applications can include:

• Turnstile control


• Fare collection systems


• Ticketing systems


• Message sign systems


• Station annunciation systems

 

Rolling stock applications can include:

• Driver console


• Mobility control unit


• Vehicle control unit


• Network video play-back


• Network video recorder


• Passenger information system


• Engine data logging and predictive maintenance

 

An example of a fixed installation with a tough environment is the station annunciation system. In larger metropolitan areas, these signs serve two functions. One function is normal information for the riders on train arrival, train destination, and so forth. Another function is mandated by Homeland Security to provide notification to people in the station in the event there is a terrorist attack or other emergency directing them to the nearest safe exit. Homeland Security became particularly concerned with safety in the rail transportation system after the Sarin attack in Tokyo in 1995. This attack was unsophisticated yet still managed to kill 12 people, severely injure 50 and cause temporary vision problems in nearly 1,000 others.

 

For security, the computer systems operating the annunciation signs are placed in track-side vaults which are located away from the platforms. There is no environmental conditioning. Equipment installed in the vault is subjected to a wide variety of adverse conditions. If the vaults are located in tunnels, the temperature is benign but the humidity levels can be high. Vaults above ground are exposed to both high and low temperatures. These are not the cleanest environments.

 

A common condition in both installations is almost constant vibration from passing trains.

 

For both the New York Transit Authority and Long Island Railroad, Chassis Plans provided semi-custom rugged 4U solutions capable of accepting the customers’ unique plug-in boards for network and sign communication and audio management and capable of reliable operation in these adverse environments. The systems were constructed with long-life components for support for the expected 5-8 year program life.

 

Chassis Plans has a long history of working with the railroad industry and can bring that experience to your project.

 

Riding the Rails is Rough

Signs Tera Technologies to Rep State of New York

Chassis Plans is pleased to announce Tera Technologies as our company representative in New York State excepting for New York City and Long Island.

 

Tera Technologies is well connected in their territory and they provide expertise in technologies complementary to Chassis Plans’ product offering of rugged military and industrial computers and displays.  They are well versed in:

 

• Single Board Computers


• Motherboards


• Industrial Computing Solutions


• Rugged Enclosures


• Backplanes


• Avionics Bus Products


• VME, VPX, cPCI, and PCI Products


• I/O Products


• Embedded Computers


• Memory Products

 

We are pleased to have the opportunity to work with Tera Technologies.

 

See www.ttechinc.com for additional information for Tera Technologies and www.chassis-plans.com/representatives.html for additional information regarding all of Chassis Plans reps.

 

 

Signs Tera Technologies to Rep State of New York

MIL-STD-810G – Part 21 (Gunfire Shock) Method 519.6

MIL-STD-810G covers Gunfire Shock in Method 519.6. Method 519.6 is comprised of 17 pages with the following annexes:

 

A – Guidelines for Procedure I (11 pages)

B – Guidelines for Procedure II (21 pages)

C – Guidelines for Procedure III (12 pages)

D – Sine-on-Random Spectrum Prediction (10 pages)

E – Guidelines for Gunfire Shock Test Scaling (7 pages)

 

Gunfire shock tests are performed to provide a degree of confidence that materiel can structurally and functionally withstand the relatively infrequent, short duration transient high rate repetitive shock input encountered in operational environments during the firing of guns. Exposure to a gunfire shock environment has the potential for producing adverse effects on the structural and functional integrity of all materiel including in-service operational capability. The probability of adverse effects increases with the blast energy of the gun, proximity of the materiel to the gun, and the duration of the gunfire shock environment. The gunfire firing rate and the duration of gunfire shock environment exposure that correspond with natural frequencies of the mounted materiel (along with its subharmonics and superharmonics) will magnify the adverse effects on the materiel’s overall integrity.

 

The gunfire environment may be considered to be a high rate repetitive shock having form of a substantial transient vibration produced by (1) an air-borne gun muzzle blast pressure wave impinging on the materiel at the gun firing rate, (2) a structure-borne repetitive shock transmitted through structure connecting the gun mechanism and the materiel, and/or a combination of (1) and (2).

 

Some of the effects of Gunfire Shock include:

 

1. changes in materiel dielectric strength, loss of insulation resistance, variations in magnetic and electrostatic field strength;


2. materiel electronic circuit card malfunction, electronic circuit card damage, and electronic connector failure. (On occasion, circuit card contaminants having the potential to cause short circuits may be dislodged under materiel response to gunfire environment);


3. permanent mechanical deformation of the materiel as a result of overstress of materiel structural and non-structural members;


4. collapse of mechanical elements of the materiel as a result of the ultimate strength of the element being exceeded.


5. accelerated fatiguing of materials (low cycle fatigue);


6. potential piezoelectric activity of materials; and


7. materiel failure as a result of cracks and fracture in crystals, ceramics, epoxies, or glass envelopes.

 

This is a very complicated Method in that the effects of air pressure pulse is combined with shock through the structure with distance from the gun having a significant impact on which input has more effect. In addition, predicting material response may be impossible.

 

The Method relies heavily on Method 525 (Time Waveform Replication).

 

There are three procedures:

 

Procedure I –

Measured in-service gunfire shock environment for materiel is replicated under laboratory exciter waveform control (Method 525 TWR) to achieve a near exact reproduction of the measured in-service gunfire shock environment.

 

Procedure II –

This procedure is based upon either (1) direct stochastic generation of time traces appropriate for Method 525 that are “equivalent” in severity to in-service measured time trace information, or (2) a procedure that may be justified for properly distributing uncertainty, and for conservative testing (but in accordance with the principles of random process theory).

 

Procedure III –

This procedure is ad hoc, lacking necessary field measured time trace information, and a last resort to providing guidelines for design of materiel to resist gunfire shock environment. Only time trace forms for design are given, and it is not suggested that testing be performed to these forms for materiel qualification purposes.

 

Gunfire Shock testing is performed on a shake table with the ability to follow test waveform inputs.

MIL-STD-810G – Part 21 (Gunfire Shock) Method 519.6

MIL-STD-810G – Part 20 (Acidic Atmosphere) Method 518.1

MIL-STD-810G covers exposure to an Acidic Atmosphere in Method 518.1. Acidic atmospheres are of increasing concern, especially for materiel in the vicinity of industrial areas or near the exhausts of fuel burning devices. Method 518.1 is comprised of 7 pages.

 

This Method is used to determine the resistance of materials and protective coatings to corrosive atmospheres. This Method is appropriate for materiel likely to be stored or operated in areas where acidic atmospheres exist, such as industrial areas or near the exhausts of any fuel-burning device.

 

Note this method is not a replacement for the salt fog method, nor is it suitable for evaluating the effects of hydrogen sulfide that readily oxidizes in the test environment to form sulfur dioxide. Caution: Although salt fog chambers are usually used for this test, introducing an acidic or sulfur dioxide atmosphere in a salt fog chamber may contaminate the chamber for future salt fog tests.

 

Some problems as a result of an acidic environment include:

 

1. Chemical attack of surface finishes and non-metallic materials.


2. Corrosion of metals.


3. Pitting of cement and optics.

 

This Method should be applied late in a products test cycle. Also, separate items should be tested for Salt Fog.

 

Two test durations are suggested. For infrequent periods of exposure, three 2-hour spraying periods with 22 hours storage after each is sufficient. To represent approximately 10 years natural exposure in a moist, highly industrial area, or a shorter period in close proximity to vehicle exhaust systems, particularly ship funnel exhausts where the potential acidity is significantly higher, four 2-hour spraying periods with 7 days storage after each is sufficient.

 

The actual test is similar to Method 509.5 (Salt Fog) in that the acid solution is atomized into a fog and blown through a test chamber.

 

MIL-STD-810G – Part 20 (Acidic Atmosphere) Method 518.1

MIL-STD-810G – Part 19 (Pyroshock) Method 517.1

MIL-STD-810G covers Pyroshock in Method 517.1. Pyroshock is a high intensity, short duration shock event caused by the detonation of a pyrotechnic device on adjacent structures. Pyroshock is a physical phenomenon characterized by the overall material and mechanical response at a structure point from either (a) an explosive device, or (b) a propellant activated device. Method 517.1 is comprised of 23 pages.

 

Method 517.1 is not intended to test material exposed to external explosions.

 

Use this method to evaluate materiel likely to be exposed to one or more pyroshocks in its lifetime.

 

In general, the pyroshock sources may be described in terms of their spatial distribution – point sources, line sources and combined point and line sources. Point sources include explosive bolts, separation nuts, pin pullers and pushers, bolt and cable cutters and pyro-activated operational hardware. Line sources include flexible linear shape charges (FLSC), mild detonating fuses (MDF), and explosive transfer lines. Combined point and line sources include V-band (Marmon) clamps.

 

Pyroshocks are generally within a frequency range between 100 Hz and 1,000,000 Hz, and a time duration from 50 microseconds to not more than 20 milliseconds. Acceleration response amplitudes to pyroshock may range from 300 g to 300,000 g.

 

Pyroshock usually exhibits no momentum exchange between two bodies (a possible exception is the transfer of strain energy from stress wave propagation from a device through structure to the materiel). Pyroshock results in essentially no velocity change in the materiel support structure.

 

The characteristics of pyroshock are:

1. near-the-source stress waves in the structure caused by high material strain rates (nonlinear material region) propagate into the near-field and beyond;


2. high frequency (100 Hz to 1,000,000 Hz) and very broadband frequency input;


3. high acceleration (300 g to 300,000 g) but low structural velocity and displacement response;


4. short-time duration (< 20 msec);


5. high residual structure acceleration response (after the event);


6. caused by (1) an explosive device or (2) a propellant activated device (releasing stored strain energy) coupled directly into the structure; (for clarification, a propellant activated device includes items such as a clamp that releases strain energy causing a structure response greater than that obtained from the propellant detonation alone);


7. highly localized point source input or line source input;


8. very high structural driving point impedance (P/v, where P is the large detonation force or pressure, and v, the structural velocity, is very small). At the pyrotechnic source, the driving point impedance can be substantially less if the structure material particle velocity is high;


9. response time histories that are random in nature, providing little repeatability and substantial dependency on the materiel configuration details;


10. response at points on the structure that are greatly affected by structural discontinuities;


11. materiel and structural response that may be accompanied by substantial heat and electromagnetic emission (from ionization of gases during explosion).

 

Examples of electronic problems associated with pyroshock follow, but the list is not intended to be all-inclusive.

1. materiel failure as a result of destruction of the structural integrity of microelectronic chips;


2. materiel failure as a result of relay chatter;


3. materiel failure as a result of circuit card malfunction, circuit card damage, and electronic connector failure. On occasion, circuit card contaminants having the potential to cause short circuits may be dislodged under pyroshock.


4. materiel failure as a result of cracks and fracture in crystals, ceramics, epoxies, or glass envelopes.

 

MIL-STD-810G – Part 19 (Pyroshock) Method 517.1

MIL-STD-810G – Part 18 (Shock) Method 516.6

MIL-STD-810G covers shock in Method 516.6. Shock is an infrequent single pulse acceleration with a narrow pulse width imparted to a device. Method 516.6 is one of the more complicated Methods comprised of 38 pages. In addition there are three Annexes:

 

Annex A – Statistical Considerations (8 pages)

Annex B – Effective Shock Duration (4 pages)

Annex C – Autospectral Density (4 pages)

 

Method 516.5 is one of the more widely performed Methods, often in conjunction with Method 514.6 (Vibration).

 

Shock tests are performed to:

1. provide a degree of confidence that material can physically and functionally withstand the relatively infrequent, non-repetitive shocks encountered in handling, transportation, and service environments. This may include an assessment of the overall material system integrity for safety purposes in any one or all of the handling, transportation, and service environments;


2. determine the material’s fragility level, in order that packaging may be designed to protect the material’s physical and functional integrity; and


3. test the strength of devices that attach material to platforms that can crash.

 

A shock environment is generally limited to a frequency range not to exceed 10,000 Hz, and a time duration of not more than 1.0 second. (In most cases of mechanical shock the significant material response frequencies will not exceed 4,000 Hz and the duration of material response will not exceed 0.1 second.) The material response will, in most cases, be highly oscillatory, of short duration, with a substantial initial rise time with large positive and negative peak amplitudes.

 

Shock is the term applied to a comparatively short time (usually much less than the period of the fundamental frequency of the material) and moderately high level (above even extreme vibration levels) force impulse applied as an input to the material.

 

Failure modes to shock events include:

 

1. material failure as a result of increased or decreased friction between parts, or general interference between parts;


2. changes in material dielectric strength, loss of insulation resistance, variations in magnetic and electrostatic field strength;


3. material electronic circuit card malfunction, electronic circuit card damage, and electronic connector failure. (On occasion, circuit card contaminants having the potential to cause short circuit may be dislodged under material response to shock.);


4. permanent mechanical deformation of the material as a result of overstress of material structural and non-structural members;


5. collapse of mechanical elements of the material as a result of the ultimate strength of the component being exceeded;


6. accelerated fatiguing of materials (low cycle fatigue);


7. potential piezoelectric activity of materials, and


8. material failure as a result of cracks in fracturing crystals, ceramics, epoxies, or glass envelopes.

 

Method 516.6 includes eight procedures:

 

Procedure I – Functional Shock

Intended to test material (including mechanical, electrical, hydraulic, and electronic) in its functional mode (as installed in the field) and to assess the physical integrity, continuity and functionality of the material to shock.

 

Procedure II – Material to be packaged

The intent of this test is to ensure the functionality of materiel after it has been inadvertently dropped before, during, or after a packaging process.

 

Procedure III – Fragility

Used to determine a material’s ruggedness or fragility so that packaging can be designed for the material, or so the material can be redesigned to meet transportation and/or handling requirements.  This test is designed to build up in severity until a test item failure occurs, or a predetermined goal is reached.

 

Procedure IV – Transit Drop

Intended for material either outside of or within its transit or combination case, or as prepared for field use (carried to a combat situation by man, truck, rail, etc.).

 

Procedure V – Crash Hazard Shock Test

Intended for material mounted in air or ground vehicles that could break loose from its mounts, tiedowns or containment configuration during a crash and present a hazard to vehicle occupants and bystanders.

 

Procedure VI – Bench Handling

Intended for material that may typically experience bench handling, bench maintenance, or packaging.

 

Procedure VII – Pendulum Impact

Intended to test the ability of large shipping containers to resist horizontal impacts, and to determine the ability of the packaging and packing methods to provide protection to the contents when the container is impacted.

 

Procedure VIII – Catapult Launch/Arrested Landing.

Intended for material mounted in or on fixed-wing aircraft that are subject to catapult launches and arrested landings.

 

 

MIL-STD-810G – Part 18 (Shock) Method 516.6

MIL-STD-810G – Part 17 (Acoustic Noise) Method 515.6

MIL-STD-810G covers Acoustic Noise Susceptibility in Method 515.6. This Method tests material’s response to very loud noise such as from a jet engine, rocket engine (think Shuttle launch) or power plant. This is not a test to determine how much noise an item generates. Method 515.6 is 8 pages with two Annexes totaling 7 pages.

 

As with most of the Methods in 810G, tailoring is essential for this Method to have any meaningful results.

 

The acoustic noise test is performed to determine the adequacy of materiel to resist the specified acoustic environment without unacceptable degradation of its functional performance and/or structural integrity. It is applicable to systems, sub-systems and units that must function and survive in a severe acoustic environment.

 

The acoustic noise environment is produced by any mechanical or electromechanical device capable of causing large airborne pressure fluctuations. In general, these pressure fluctuations are of an entirely random nature over a large amplitude range (5000 Pa to 87000 Pa), and over a broad frequency band extending from 10 Hz to 10000 Hz. When pressure fluctuations impact materiel, generally, a transfer of energy takes place between the energy (in the form of fluctuating pressure) in the surrounding air to the strain energy in materiel. This transfer of energy will result in vibration of the materiel, in which case the vibrating materiel may re-radiate pressure energy, absorb energy in materiel damping, or transfer energy to components or cavities interior to the materiel.

 

Some of the effects of a high acoustic environment include:

 

1. Wire chafing


2. Component acoustic and vibratory fatigue


3. Component connecting wire fracture


4. Cracking of printed circuit boards


5. Failure of wave guide components


6. Intermittent operation of electrical contacts


7. Cracking of small panel areas and structural elements


8. Optical misalignment


9. Loosening of small particles that may become lodged in circuits and mechanisms


10. Excessive electrical noise

 

As with Method 514.6 (Vibration), loud acoustic environments can have an effect on the material that may change the material’s response to other tests. For example, noise can cause a vibration is a panel that cracks the finish which would cause a failure of the Salt Fog test. This test should be performed first or in conjunction with vibration testing.

 

The Method provides three procedures:

 

Procedure I – Diffuse Field Acoustic Noise.

A uniform intensity shaped spectrum of acoustic noise that impacts all the exposed materiel surfaces is provided. This would be a typically noisy environment with broadband widespread noise such as produced by aerospace vehicles or power plants.

 

Procedure II – Grazing Incidence Acoustic Noise.

Includes a high intensity, rapidly fluctuating acoustic noise with a shaped spectrum that impacts the materiel surfaces in a particular direction – generally along the long dimension of the materiel. An example is high speed airflow over the skin of an aircraft or airflow around a missile hanging on a wing pylon.

 

Procedure III – Cavity Resonance Acoustic Noise.

The intensity and, to a great extent, the frequency content of the acoustic noise spectrum is governed by the relationship between the geometrical configuration of the cavity and the materiel within the cavity. An example would be an open weapons bay on a fighter where the air in the cavity is turbulent. This can induce vibration in adjacent aircraft structures and equipment such as bombs or missiles still in the bay.

 

 

MIL-STD-810G – Part 17 (Acoustic Noise) Method 515.6

MIL-STD-810G – Part 16 (Vibration) Method 514.6

MIL-STD-810G covers vibration in Method 514.6. This is one of more commonly applied Methods. The Method is 23 pages long plus the following annexes.

 

Engineering Information Annex A – 11 pages

Manufacture / Maintenance Guidance Annex B – 1 page

Transportation Tailoring Guidance Annex C – 23 pages

Operational Tailoring Guidance Annex D – 22 pages

Supplemental Tailoring Guidance Annex E – 8 pages

 

As can be noted, while this is one of the more commonly referenced Methods, it is also potentially the most complex to adequately tailor the tests to the operational environment. It can also be noted that laboratory testing is only a close approximation to real-world exposure.

 

The Method starts with a note stating tailoring is essential. Material in the field is subject to a wide variety of vibration amplitudes and frequencies. Items carried in the back of a truck experience much different vibration than items mounted to a helicopter airframe. The appropriate test must be carefully thought out depending on the end-use environment.

 

Of particular note is Method 514.6 is limited to consideration of one mechanical degree-of-freedom at a time. That is, a shake table used for testing moves in only one axis at a time. Method 527 provides further guidance on multiple exciter testing.

 

The Method discusses the item Vibration Life Cycle including:

 

• Manufacture / Maintenance


• Transportation


• Operational


• Supplemental

 

Within each of these domains, sub-categories such as truck and trailer transportation, aircraft transportation, watercraft transportation and railroad transportation exist. Each of these categories may be again sub-divided into yet more specific criteria such as jet, propeller, helicopter for aircraft.

 

Of concern is the coupling of the unit under test to the mounting platform. Care must be taken, especially for larger items, that flexing and the dynamic responses of the mounting platform during testing do not change the test results to not reflect the real-world environment.

 

The effects of vibration and items to look for include:

 

1. Chafed wiring.


2. Loose fasteners/components.


3. Intermittent electrical contacts.


4. Electrical shorts.


5. Deformed seals.


6. Failed components.


7. Optical or mechanical misalignment.


8. Cracked and/or broken structures.


9. Migration of particles and failed components.


10. Particles and failed components lodged in circuitry or mechanisms.


11. Excessive electrical noise.


12. Fretting corrosion in bearings.

 

Essentially all material will experience vibration, whether during manufacture, transportation, maintenance or operational use. Vibration can have deleterious effects on the unit under test such as cracked finishes, displaced seals, etc. As such, vibration testing should be accomplished prior to other environmental tests to assure vibration doesn’t cause other hidden problems. For example, stress cracks in the material finish due to flexing of the material would show up as corrosion in Method 509.5 (Salt Fog) while a new un-flexed part would pass.

 

Method 514.6 provides 4 procedures:

 

Procedure I – General Vibration

Used for material to be transported as secured cargo or deployed for use on a vehicle including ground vehicles and fixed and rotary wing aircraft.  Standard laboratory vibration shakers are used for testing.

 

Procedure II – Loose Cargo Transportation

Used to simulate unsecured items carried in or on trucks, trailors or tracked vehicles. Simulation of this environment requires use of a package tester  that imparts a 25.4 mm (1.0 inch) peak-to-peak, circular synchronous motion to the table at a frequency of 5 Hz.

 

Procedure III – Large Assembly Transportation

Intended to replicate the vibration and shock environment incurred by large assemblies installed or transported by wheeled or tracked vehicles.  The item under test is loaded onto a representative vehicle and the vehicle is then driven over a test surface to simulate service conditions.

 

Procedure IV – Assembled Aircraft Store Captive Carriage and Free Flight

Used for fixed wing aircraft carriage and environmental life cycles of all aircraft stores and free flight phases of ground or sea-launched missiles.  Standard laboratory vibration shakers are used for testing using representative mounting points to simulate aircraft mounting.

 

Large test items on large complex fixtures are almost certain to have fixture resonances within the test range which can result in large over-tests or under-tests. Similar problems often occur with small test items.

 

Analyses of vibration related failures must relate the failure mechanism to the dynamics of the failed item and to the dynamic environment. It is insufficient to determine that something broke due to high cycle fatigue or wear.

 

Materiel is deemed to have failed if it suffers permanent deformation or fracture; if any fixed part or assembly loosens; if any moving or movable part of an assembly becomes free or sluggish in operation; if any movable part or control shifts in setting, position or adjustment, and if test item performance does not meet specification requirements while exposed to functional levels and following endurance tests.  A vibration qualification test is complete when all elements of the test item have successfully passed a complete test. When a failure occurs, stop the test, analyze the failure, and repair the test item. Continue the test until all fixes have been exposed to a complete test.

 

 

MIL-STD-810G – Part 16 (Vibration) Method 514.6

MIL-STD-810G – Part 15 (Acceleration) Method 513.5

MIL-STD-810G covers steady-state acceleration experienced by material in the service environment. The Method is used to assure material continues to operate after testing.  The Method is also used to assure the material does not become hazardous after exposure to inertial loads experienced in a crash. The method is applicable to material that is installed in aircraft, helicopters, manned aerospace vehicles, air-carried stores, and ground/sea-launched missiles. Method 513.5 is 13 pages long plus a 6 page annex discussing Test Considerations .

 

Method 513.5 includes a note stating that tailoring is essential. A large part of the Method is devoted to tailoring the tests to the material and intended environment.

 

This Method is different from Method 514.6 (Vibration) and Method 516.6 (Shock) in that the acceleration is applied slowly enough with sufficient time allowed to fully distribute the resulting loads through the material and dynamic response of the material is not excited. This method is not adequate for testing aerodynamic loads. Method 501.5 (High Temperature) should be conducted prior to this Method.

 

The effects of acceleration include:

 

1. Structural deflections that interfere with materiel operation.


2. Permanent deformation, structural cracks, and fractures that disable or destroy materiel.


3. Broken fasteners and supports that result in loose parts within materiel.


4. Broken mounting hardware that results in loose materiel within a platform.


5. Electronic circuit boards that short out and circuits that open up.


6. Inductances and capacitances that change value.


7. Relays that open or close.


8. Actuators and other mechanisms that bind.


9. Seals that leak.


10. Pressure and flow regulators that change value.


11. Pumps that cavitate.


12. Spools in servo valves that are displaced causing erratic and dangerous control system response.

 

Section 2 provides formulas for determining g-loads for fighter aircraft because of the high roll and pitch rates and tables of suggested g-loads for other platforms such as helicopters, manned aerospace vehicles, ground-launched missiles, etc. There is also a table of suggested g-loads for the Crash Hazard Acceleration test which goes up as high as 40-g.

 

Required apparatus for testing consists of either a centrifuge of adequate size or a rocket-powered sled.

 

This Method provides for three procedures:

 

1. Procedure I – Structural Test
   
   The item under test is subjected to the specified g-level while not operating. After the test, test the item for proper operation.


2. Procedure II – Operational Test
   
   The item under test is turned on and operating normally while subjected to the g-load.


3. Procedure III – Crash Hazard Acceleration Test
   
   Very high non-operational g-loads are imparted to assure the item under test does not become a hazard during a crash. Items, such as aircrew seats, are tested to ensure they remain attached to the aircraft structure during a crash.

MIL-STD-810G – Part 15 (Acceleration) Method 513.5

MIL-STD-810G – Part 13 (Immersion) Method 512.5

810G covers Emmersion or partial Emmersion in water (or salt water) of equipment. This Method is 7 pages long.

 

This is a rather simple Method. The goal of the tests are to check the item for leaks when submerged in water. There are two Procedures:

 

I. Immersion or submersion

II. Fording

 

Effects of immersion include:

 

1. Fouling of lubricants between moving parts.


2. Formation of electrically conductive paths which may cause electrical or electronic equipment to malfunction or become unsafe to operate.


3. Corrosion due to direct exposure to the water or to the relatively high humidity levels caused by the water.


4. Impairment of the burning qualities of explosives, propellants, fuels, etc.


5. Failure of vehicle engines to operate.

 

For the Immersion test (Procedure I), the item is submerged so the top of the item is 1M below the surface. If the environment anticipates a deeper depth, it may be necessary to use a chamber and pressurize to the test depth, assuring the top of the test item is fully submerged.

 

The Fording test (Procedure II) is primarily targeted at vehicles traversing a body of water or material secured to such vehicles.

 

One facet of the Immersion test to consider is the item under test should be heated 27 deg C above the water temperature. When the item is submerged in the cooler water, it will cool down and the inside pressure will be lower. This may “suck” water into the item. 27 Deg C is specified to simulate solar heating. Otherwise, use 10 deg C as a differential to simulate normal differences between material and water temperature.

 

The Immersion test should last approximately 30 minutes. The Fording test should last an hour.

 

Prior to testing, doors, valves, etc., should be exercised a minimum of 3 times to assure seals are not sticking to the surfaces.

 

After the test, examine the article for leaks. Air bubbles during the test are a good indication of a leak. Weight before and after the test may be a good indication of a leak.

 

As a side note, the immersion test may be used for the rain test. However, rain dynamics can sometimes compromise seals so both rain and immersion tests should be conducted.

 

MIL-STD-810G – Part 13 (Immersion) Method 512.5

MIL-STD-810G – Part 13 (Explosive Atmosphere) Method 511.5

810G covers equipment operated in an Explosive Atmosphere. Method 511.5 is 8 pages long. This Method is performed to:

 

1. Demonstrate the ability of materiel to operate in fuel-air explosive atmospheres without causing ignition, or


2. Demonstrate that an explosive or burning reaction occurring within encased materiel will be contained, and will not propagate outside the test item.

 

This method applies to all materiel designed for use in the vicinity of fuel-air explosive atmospheres associated with aircraft, automotive, and marine fuels at or above sea level. Procedure II specifically relates to atmospheres in a space in which flammable fluids or vapors exist, or can exist, either continuously or intermittently (e.g., in fuel tanks or within fuel systems).

 

The Method provides for two Procedures:

 

I – The item under test operating in an explosive atmosphere without igniting the air/fuel mixture environment.

II – Determine the ability of the test item to contain an explosion or flame that is the result of an internal malfunction.

 

The test involves placing the item under test inside a chamber that is filled with an explosive mixture of air and n-hexane. N-hexane is specified because its ignition properties in flammable atmospheres are equal to or more sensitive than the similar properties of 100/130-octane aviation gasoline, JP-4 and JP-8 jet engine fuel.

 

The chamber is maintained at the maximum temperature the item may experience. Also, altitude is simulated as appropriate. The energy required to ignite a fuel-air mixture increases as pressure decreases.

 

For Procedure I, operate the item in an explosive atmosphere to determine if it will ignite the mixture.

 

For Procedure II, introduce an explosive mixture into the test item and ignite that mixture. Assure the resulting explosion is contained inside the test item and does not ignite the explosive mixture in the chamber.

 

MIL-STD-810G – Part 13 (Explosive Atmosphere) Method 511.5

Mil-Std-810G – Part 12 (Sand and Dust) Method 510.5

810G covers exposure of equipment to dry blowing sand and dust. Think Afghanistan. As with Method 509.5 for Salt Fog exposure, Blowing Sand and Dust is one of the more commonly performed tests. Method 510.5 covers 13 pages. This is one of the shorter duration Methods and can be finished in a day.

 

Dust is defined as particles measuring less than 150um and sand measures in the range of 150 to 850um. There are specs for size distribution within that range for the test dust or sand.

 

Dust exposure is examined for the ability of the item under test to resist vents being clogged, penetration through cracks, crevices, bearings and joints and to evaluate the effectiveness of filters.

 

Sand exposure is designed to test the item for its ability to be stored and operated in blowing sand conditions. Blowing sand can be very erosive, easily stripping the finish from an item allowing subsequent corrosion or operational failure. Blowing sand can quickly render optical devices unusable.

 

This method is not used to evaluate in-flight material such as air frames, propellers, helicopter rotors, etc. due to the velocities involved. This Method is also not used to evaluate the build-up of electrostatic charge. Some care should be exercised with the equipment regarding ESD. Blowing sand and dust can impart a fairly high charge on an item and subsequent handling of the item may cause damage from a discharge. Assure the item and operator are grounded before handling during or after a test.

 

Blowing sand and dust is usually associated with hot-dry regions though it can be experienced in most other regions depending on the season and weather. In addition, military operations can generate large quantities of loose sand and dust which can be picked up by the wind or, potentially, rotorcraft or other aircraft.

 

The effects can include:

 

1. Abrasion and erosion of surfaces.


2. Penetration of seals.


3. Degradation of electrical circuits.


4. Obstruction/clogging of openings and filters.


5. Physical interference with mating parts.


6. Fouling/interference of moving parts.


7. Reduction of thermal conductivity.


8. Interference with optical characteristics.


9. Overheating and fire hazard due to restricted ventilation or cooling.


10. Wear (increased fretting due to imbedding between mating surfaces).


11. Increased chaffing between non-mating contacting surfaces.


12. Weight gain, static/ dynamic balance.

 

Because of potential damage to an article, Humidity, Salt Fog and Fungus Growth testing should be accomplished prior to Blowing Sand and Dust testing. Also consider the corrosive effects of dust or dust residue since salt and highly alkaline materials may be present in the end-use environment.

 

Method 510.5 provides two procedures:

Procedure I – Blowing Dust (less than 150um)

Procedure II – Blowing Sand (150 to 850um)

 

As you will recall, MIL-STD-810G is not a set of tests to pass or not pass but a document guiding the creation of test procedures which are agreed upon between the vendor and customer as to the intended environment. Therefore, part of the process for Method 510.5 is to identify the climatic conditions appropriate for the geographic areas in which the material will be operated and stored. Specific test conditions should be based, if possible, on field data. Method 510.5 offers guidance which can be used in the absence of field data.

 

The test itself, while straight forward, can be brutal.

 

For Blowing Dust, the item under test should be maintained at its high operating or storage temperature. Humidity should be maintained below 30 percent. The air velocity for the test should be a minimum of 300 +/-200 feet/min with a higher velocity of 1750 +/-250 feet/min typical of desert winds. Use local conditions if they are more representative of the intended environment. The dust should have a chemical composition similar to the dust found in the intended environment. For example, in arid regions, soluble salts are common and can cause fouling, corrosion, and electrical shorts. If possible, actual dust from the region should be used in the test. The goal is to have as realistic test as possible.

 

The item under test should be rotated to assure all surfaces face the blowing dust.

 

The test duration should be at least 6 hours at ambient temperature with an additional 6 hours at the high storage or operational temperature.

 

For Blowing Sand, the test is very similar regarding temperature and humidity. However, the velocity is increased to 40-65 mph (3500-5700 ft/sec). The material should be common silica sand. As with Dust testing, it is preferred to match the properties of the sand found in the end-use environment to the test sand. There are 90 deserts in the world, each with different particle size distributions.

 

The quantity of sand in the air during the test is determined by the expected environment:

 

1. For materiel likely to be used close to helicopters operating over unpaved surfaces: 2.2 ± 0.5 g/m3.


2. For material never used or exposed in the vicinity of operating aircraft, but which may be used or stored unprotected near operating surface vehicles: 1.1 ± 0.3 g/m3.


3. For material that will be subjected only to natural conditions: 0.18 g/m3, -0.0/+0.2 g/m3.

 

The item under test should be oriented so that the most vulnerable surface faces the blowing sand. Rotate the item every 90 minutes if more than one vulnerable surface exists.

 

The Blowing Sand test should last 90 minutes per vulnerable face.

 

For Blowing Dust, evaluate the item for binding, clogging, seizure, etc. Does it operate correctly? Check air filter operation to assure the filters are up to the task.

 

For Blowing Sand, evaluate the item for abrasion and operation. Examine protective coatings and seals. Does the item operate correctly?

 

Chassis Plans has taken our military chassis and displays through Blowing Sand and Dust testing and can work with the customer to put a plan in place for 810G compliance.

 

Mil-Std-810G – Part 12 (Sand and Dust) Method 510.5

Adds Reps Coverage to CA, NV, OR, WA, ID, MT and WY

We’re rounding out our national sales coverage by adding two new rep organizations.

 

Advanced Packaging, Inc.

Responsible for Washington, Oregon, Idaho, Montana, and Wyoming.  Advanced Packaging is known for their military grade packaging solutions with both East and West Coast presence.

 

See www.advpack.com for more information for Advanced Packaging.

 

Middle Canyon, LLC

Responsible for California North of Santa Barbara and Nevada. The principles of Middle Canyon have been in the military and industrial computer business since business for 30+ years and will be invaluable in helping our customers with their projects.

 

See www.middlecanyon.com for additional information for Middle Canyon.

 

See www.chassis-plans.com/representatives.html for additional information regarding all of Chassis Plans reps.

 

 

Adds Reps Coverage to CA, NV, OR, WA, ID, MT and WY

Mil-Std-810G – Part 11 (Salt Fog) Method 509.5

This is part 11 of a series delving into the intricacies of Mil-Std-810G.

 

810G covers accelerated corrosion using salt fog in Method 509.5.  This method comprises 10 pages. This is one of the more commonly performed tests and is definitely required for items sold to the Navy or for use in coastal areas. Salt is one of the most pervasive chemical compounds in the world. It is found in the oceans and seas, the atmosphere, ground surfaces, and lakes and rivers. It is impossible to avoid exposure to salt.

 

The purpose of Method 509.5 is to assess the effectiveness of protective coatings and finishes on materials. All unprotected metals will corrode if not protected with some finish such as plating or paint. Finishes can also have pinholes or cracks allowing salt to reach the underlying material, causing corrosion. The Method can also be applied to determine the effects of salt deposits on the physical and electrical aspects of the assembly.

 

The effects of a corrosive environment include:

 

1. Corrosion effects such a electrochemical reaction, stress corrosion, and the formation of acidic/alkaline solutions


2. Electrical effects such as impairment of electrical material due to salt deposits, production of conductive coatings causing short circuits, and corrosion of insulating materials.


3. Physical effects such as clogging or binding of moving parts and blistering of paint as a result of underlying electrolysis.

 

Use Method 509.5 for screening purposes only to evaluate the effectiveness and quality of protective coatings and finishes. Either coupons (samples) or the final assembly can be evaluated. The Method is not representative of the natural environment but is a good indicator of potential problem areas. In general, only apply this Method to material that will experience significant exposure to high levels of salt in the atmosphere, such as ship board applications.

 

The Method lists six limitations as follows:

 

1. There is no relationship between this test and any real world exposure duration.


2. It has not been demonstrated that a direct relationship exists between salt fog corrosion and corrosion due to other media.


3. This test has does not imply the material will survive under all corrosive conditions.


4. This test is unreliable for predicting the service life of materials in corrosive conditions.


5. Effects of humidity and fungus growth are not represented in this test.


6. This test is not intended to be used for sample or coupon testing in lieu of assemblage testing.

 

The Method requires a 5% (+/-1%) salt fog be produced and circulated (with minimal air velocity) around the item under test. Condensation should not be allowed to drip onto the test items. This is a fog test, not a salt water exposure test. The test is recommended to last 48 hours with a 48 hour drying time although an alternating 24 hour test cycle (24 fog, 24 drying, 24 fog, 24 drying) has proven to be more destructive. The test temperature is specified as 35 deg C which has been historically accepted and is not necessarily indicative of the actual environment. Alternate temperatures can be used as appropriate.

 

In general, test samples from the salt fog test should not be used in other tests. If only one sample is available or a sample must be reused for other tests, in terms of a schedule, humidity and fungus growth testing should be performed before the salt fog test and sand and dust testing after the salt fog test.

 

After the test, the item should be inspected for physical, electrical and corrosion effects. There can be surprising results. We tested a sample rear panel with a nickel finish compared to a zinc plated finish. As it turned out, the more expensive nickel had apparent pinholes in the finish and failed miserably while the much less expensive zinc coating showed only a light surface corrosion with no damage to the underlying metal.

 

Chassis Plans has worked with various customers to define test procedures, as required by MIL-STD-810G, to validate our rugged rackmount computer systems and displays.

 

Mil-Std-810G – Part 11 (Salt Fog) Method 509.5

Mil-Std-810G – Part 10 (Fungus Growth)

This is part 10 of a series delving into the intricacies of Mil-Std-810G.

 

810G covers fungus growth in Method 508.6.  This method comprises 11 pages plus a 1 page annex on decontaminating equipment after the tests and a 1 page annex on fungus-inert materials.

 

The purpose of Method 508.6 is to assess the extent to which materiel will support fungal growth and how any fungal growth may affect performance or use of the materiel. The primary objectives of the fungus test are to determine:

 

1. if the materials comprising the test object, or the assembled combination of same, will support fungal growth, and if so, of what species.


2. how rapidly fungus will grow on the materiel.


3. how fungus affects the materiel, its mission, and its safety for use following the growth of fungus on the material.


4. if the material can be stored effectively in a field environment.


5. if there are simple reversal processes, e.g., wiping off fungal growth.

 

Because some other tests in 810G such as salt fog, sand and dust, or humidity can change the results of a fungus test, those tests should be conducted on a sample after the fungus test is complete. It is imperative the sample be decontaminated after the fungus tests.

 

Electronic equipment is typically manufactured using fungus-resistant material such as fiberglass, metal, plastic, etc. Materials affected by fungus such as fabrics are not typically used in electronic equipment. However, fungus growth can still have detrimental effects on electronic circuitry.

 

The detrimental effects of fungus growth can include:

 

• Natural material – products such as paper, natural fibers, fabric, etc., are most susceptible as they can feed the fungus. Other organic materials such as adhesives, grease, oils, etc. and leather are susceptible.


• Synthetic materials – PVC formulations, some polyurethanes, plastics with organic fillers and paints or varnishes with susceptible constituents.

 

Effects of indirect attack include:

 

• Fungal growth on surface deposits of dust, grease, or other contaminants can cause damage to the underlying material.


• Metabolic waste products of the fungus (organic acids) can cause corrosion of metals, etching of glass, or staining or degrading of plastics and other materials.


• Fungus growth can bridge sensitive circuitry changing the electrical properties.


• Fungus can affect optical systems by adversely affecting light transmission through the system or block delicate moving parts.

 

The Method includes a warning note that 1) highly-specialized techniques are required for the analysis and 2) simple analysis is not sufficient and testing should be performed.

 

Fungus growth can have a negative health impact as many people are very sensitive to mold and fungus.

 

This is a long test, lasting 28 days as a minimum, to allow germination, break-down of carbon-containing molecules, and degradation of the material. In addition, it is recommended the test be extended to 84 days to fully evaluate the impact of fungus growth.

 

The Method identifies five different varieties of fungus which are known to affect different materials and are distributed worldwide. Other species can be introduced as required.  It is recommended to only use 5 or 6 species for testing. The more dominant species will prevail in testing and adding additional species will only add to the cost without additional degradation to the underlying material.

 

The test requires a relatively sophisticated chamber to maintain the desired humidity and temperature as these greatly impact fungus growth. The chamber needs to be vented and filtered to release pressure changes and to filter fungus spores from the discharge.

 

The method goes into great detail on cleaning the test items and the chamber. In addition, while the fungi used in the tests are not typically harmful to humans, some people may have or may develop allergies or other reactions so good housekeeping and handling precautions should be observed.

 

As mentioned earlier, this is a sophisticated test and requires trained personnel and specialized laboratory equipment such as a centrifuge to properly administer the test. The fungal spores need to be prepared and tested for viability. Control strips of cotton are prepared and hung adjacent to the test specimen to be exposed as much as possible to the conditions the specimen is seeing.

 

After the test period, the material under test is analyzed for the fungus species, extent of growth, impact on the underlying material, long range effect the growth could have on the material, and the specific nutrients supporting the growth.

 

Chassis Plans has worked with various customers to define test procedures, as required by MIL-STD-810G, to validate our rugged rackmount computer systems and displays.

 

Mil-Std-810G – Part 10 (Fungus Growth)

Chassis Plans Secures Million Dollar Contract for New York Transit Authority

Rugged 4U Computer System

Chassis Plans has been chosen to provide rugged computer systems to the New York Transit Authority for station upgrades for the passenger and train station annunciation systems.  These annunciation systems are used for both audio and text based announcements for normal station operation and in the advent of an emergency or terrorist attack.

 

These rugged systems are placed in track-side vaults subject to heavy vibration and extreme temperature swings.

 

This contract is a follow-on to the original station build-out contract. Chassis Plans is providing rugged long-life rackmount computer systems.

 

Chassis Plans Secures Million Dollar Contract for New York Transit Authority

Chassis Plans Launches New Rugged Storage Server

Chassis Plans (www.chassis-plans.com) has launched a new Rugged Storage Server, this is a purpose built server used for storing and accessing small to large amounts of data over a shared network.  The storage server is an integral part of the networked storage resources and can be configured as network attached storage (NAS) or other storage device / networking technologies.

 

This system is packed in a 2U 20.1 inch depth aluminum chassis with a ¼ inch front panel for improved rigidity and ruggedness. This system is designed with high speed data recording through the use of rotating or solid state drives (SSD) disks. This rugged solution provides up to 12 Terabytes (TB) of storage capacity with rotating drives or 7.2 TB with solid state drives.

 

The system incorporates an 8 Core Intel Xeon processor, 8GB of Memory, includes (6X) shock isolated 2.5” drive bays, 1 x slim optical bay. System includes reusable air filters and a black anodized finish. Custom colors are available upon request.

 

The system is designed to meet MIL-STD’s 810f and 461.

Chassis Plans Launches New Rugged Storage Server