IEC 60068 Explained: A Deep Dive into Vibration Testing Standards

What is IEC 60068 Vibration Testing?

IEC 60068-2 is a subset of the broader IEC 60068 series, which sets out international test standards for various environmental tests on products, equipment, and components. Included within the IEC 60068-2 series are the vibration test standards:

• IEC 60068-2-6 Environmental testing Part 2-6: Test Fc: Vibration (sinusoidal)
• IEC 60068-2-64 Environmental testing Part 2-64: Test Fh: Vibration, Broadband Random, and Guidance

DES has extensive experience performing many vibration tests to IEC 60068-2-6 and IEC 60068-2-64.  We are A2LA accredited to those standards. 

Why perform IEC 60068 Vibration Testing?

• All products will likely experience some vibration during their lifetime from shipping and transportation.  Thus, some level of vibration testing is valuable. 
• For items being sold outside of the USA, the results from vibration testing to IEC 60068-2-6 and IEC 60068-2-64 are accepted worldwide.  
• IEC 60068-2-6 and IEC 60068-2-64 can be used to evaluate the reliability and performance of products that will be exposed to vibration environments.
• They are useful to assess the durability and performance of connectors exposed to harsh conditions such as military, automotive, and space environments.  During the vibration, the connectors are monitored for intermittent electrical contact with specialized equipment provided by DES. 
• Manufacturers can validate the structural integrity of items and identify possible degradation under different vibration conditions. 
• Automotive and aerospace suppliers can evaluate the reliability, durability, and performance of their components that are subjected to intense vibration during their lifetime.
• IEC 60068-2-6 and IEC 60068-2-64 can be used to investigate structural dynamic characteristics for items used in spacecraft programs.
• Testing to these standards can simulate the stresses that occur during the life of a product giving confidence in its performance and longevity.
• Products can be developed to function and withstand vibration exposures encountered during their life cycle.
• Companies can evaluate the durability and performance of components, equipment, and articles during transportation and service vibration.

IEC 60068-2-6: Sinusoidal Vibration Test Standard

IEC 60068-2-6 is a test standard for Sinusoidal Vibration Testing.  It defines a procedure for testing specimens to sinusoidal vibrations over a specified frequency range for a given duration.  It is applicable (but not limited) to products or components that are subjected to harmonic vibrations such as rotating, pulsating, or oscillating forces that occur in ships, aircraft, land vehicles, rotorcraft, machinery, space applications, and seismic events. 

Much of the IEC 60068-2-6 specification deals with controlling the test parameters.  Other parts cover various test severities such as the vibration amplitude, frequency ranges, and durations.  It is up to the user to choose which test severities are applicable to their products.  Annex A in IEC 60068-2-6 gives some guidance on testing.  Annexes B and C provide examples of severities based on different applications.  The user must also specify whether the specimen shall be functional during the vibration test or whether it can be functionally tested before and after. 

IEC 60068-2-6 endurance testing can be accomplished either by endurance by sweeping or endurance at fixed frequencies.  Endurance by sweeping is performed by continuously sweeping or varying the sinusoidal vibrations from the lowest to the highest to the lowest frequencies for a chosen number of sweep cycles.  Endurance at fixed frequencies is completed by subjecting the specimens to a sine dwell at the product resonances for a fixed duration and vibration amplitude.

Contact DES today to discuss your IEC 60068-2-6 vibration testing requirements with one of our experts.

The Random Vibration Test: An In-depth Look at IEC 60068-2-64

IEC 60068-2-64 is a procedure for Random Vibration Testing of components, products and equipment.  Random vibration occurs in transportation environments, vehicles, aircraft, aerospace, military environments, etc.  Random vibration tests can also be useful for evaluating the general robustness and durability of products and components.  IEC 60068-2-64 defines requirements for subjecting specimens to broadband random vibration tests over a specified frequency range for a given duration.  It is primarily intended for specimens that are unpackaged, however, a packaged product can be tested using transportation vibrations. 

The first part of IEC 60068-2-64 covers controlling the test parameters.  Subsequent parts of IEC 60068-2-64 list various test severities such as the Grms value of acceleration, the frequency range, and the duration of testing.  Similar to IEC 60068-2-6, the user chooses what test severities to apply to their products and if the specimen shall be functional during the vibration test or whether it should be functionally tested before and after.  Annex A in IEC 60068-2-64 provides examples of severities based on different applications.  Annexes B and C provide information and guidance. 

An optional low-level vibration response investigation (sometimes called a resonance scan or modal survey) can be performed before and after the random vibration in each axis.  The vibration response investigation can be either a sinusoidal vibration sweep or random vibration applied for a short duration.  In either case, the vibrations should be low level to avoid damaging the test specimen but high enough to excite resonances.  

Completing the Vibration Test

Once all the severities are chosen in either IEC 60068-2-6 or IEC 60068-2-64, the testing is performed along three perpendicular axes, one at a time.  Upon completion of the vibration test, DES will promptly deliver a detailed test report that includes the customer’s name and address, the test dates, a summary of the test procedure, chosen severities, equipment & measuring system calibration information, operational test data, test observations & results, color pictures of the vibration test setup and color pictures of any failures. 

Secure your product’s market success with DES’s comprehensive random vibration testing services. Contact us now and let’s get started.

DES Your Go-To for IEC 60068 Compliant Vibration Testing

Choosing the right partner for your vibration testing needs is crucial. At Delserro Engineering Solutions, we offer a comprehensive suite of services designed to ensure your products meet the stringent IEC 60068 standards. Here’s why DES should be your first choice:

• Customized Solutions: We design and fabricate your vibration test fixtures tailored to your specific needs.
• Precision and Care: Our test setup process is meticulous, incorporating control and response accelerometer placement, correct bolt torque application, and organized cable routing.
• Quality Assurance: As an accredited laboratory, we adhere to IEC 60068-2-6 and IEC 60068-2-64 test standards, ensuring quality and compliance.
• Advanced Facilities: With our state-of-the-art testing facilities and equipment, we are equipped to handle a wide range of vibration test requirements.
• Extensive Experience: Our team has a broad range of experience in vibration testing, including products used in outer space, rockets, missiles, automotive and truck environments, military environments, and medical environments.

Contact DES today to discuss your vibration testing requirements with one of our experts. 

If you want to learn more about different types of vibration testing, please read these related blog articles:

• Sinusoidal and Random Vibration Testing Primer
• Mixed Mode: Sine on Random Vibration Testing
• Extreme Combined Temperature & Vibration Testing

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ISTA 1 tests are Non-Simulation Integrity Performance Tests meant to evaluate the strength and robustness of the product and package combination.  Each of the ISTA 1 test procedures (1A, 1B, 1C, 1D, 1E, 1G, and 1H) include a combination of tests to assess the ability of packaging to withstand different transportation hazards. These tests help manufacturers and distributors identify weaknesses in their packaging and product designs, and ultimately make improvements to ensure products arrive at their destinations in good condition. All ISTA 1 tests share the common goal of minimizing potential shipping issues and product damage during transportation.

What are the benefits of ISTA Series 1 Package Tests?  They can:

• Evaluate the durability of individually packaged products
• Compare the performance of various package and product design alternatives
• Test that your products will arrive unharmed at their destination
• Provide a cost-effective screening test to evaluate potential shipping issues or product damage
• Shorten package development time and gain confidence before launching products

The ISTA 1 tests are divided into the following procedures:

• ISTA 1A, Integrity Testing for Packaged-Products weighing 150 lb. (68 kg) or Less
• ISTA 1B, Integrity Testing Packaged-Products weighing Over 150 lb. (68 kg)
• ISTA 1C, Extended Integrity Testing for Individual Packaged-Products weighing 150 lb. (68 kg) or Less
• ISTA 1D, Extended Integrity Testing for Individual Packaged-Products weighing Over 150 lb. (68 kg)
• ISTA 1E, Integrity Testing for Unitized Loads
• ISTA 1G, Packaged-Products weighing 150 lb. (68 kg) or Less utilizing Random Vibration
• ISTA 1H, Integrity Testing for Packaged-Products weighing Over 150 lb. (68 kg) utilizing Random Vibration

ISTA 1A to ISTA 1E: Packaging Up to 150 Pounds and above (1B, 1D, 1E)

ISTA 1A Package Testing

ISTA 1A is a package test procedure for individually packaged products weighing up to 150 pounds. The table below provides the test sequence required for ISTA 1A.  ISTA 1A is the same as ISTA 1G except for the vibration.  ISTA 1A uses fixed displacement vibration while ISTA 1G specifies random vibration.

ISTA 1B Package Testing

ISTA 1B is a protocol for individually packaged products weighing more than 150 pounds. ISTA 1B is the same as ISTA 1H except that ISTA 1B specifies fixed displacement vibration whereas 1H uses random vibration. The table below provides the test sequence required for ISTA 1B. 

ISTA 1C Package Testing

ISTA 1C is an extended package test procedure designed for individually packaged products weighing 150 pounds or less.  ISTA 1C adds compression testing vs. 1A or 1G and gives alternative choices for vibration.  The test sequence is listed below.

ISTA 1D Package Testing

ISTA 1D is an extended test protocol for individually packaged products weighing more than 150 pounds.  ISTA 1D is the same as 1B or 1H with the addition of compression testing and alternative choices for vibration.  The test sequence is shown below. 

ISTA 1E Package Testing

ISTA 1E is for testing unitized (palletized) loads made up of either single or multiple products or packages of the same products.  The test sequence is shown below. 

Vibration and Shock Testing for Packages Up to 150 lb (ISTA 1G) & above (ISTA 1H)

ISTA 1G Package Testing

ISTA 1G is a package test procedure applicable to individually packaged products weighing 150 pounds or less.  Like ISTA 1A, it evaluates the strength and robustness of the product and package combination without simulating actual environmental conditions.  The primary difference between ISTA 1A and ISTA 1G is the vibration testing, with ISTA 1A using fixed displacement vibration and ISTA 1G specifying random vibration.

ISTA 1H Package Testing

ISTA 1H is a protocol for individually packaged products weighing more than 150 pounds. ISTA 1H is the same as ISTA 1B with the exception that ISTA 1H specifies random vibration. The test sequence is listed below. 

ISTA 1 Series: Comprehensive Testing for Optimal Product Shipping and Delivery

ISTA package testing standards play a pivotal role in ensuring that products arrive in optimal condition at their destinations. These tests help manufacturers and distributors evaluate the durability and performance of their packaging and compare different packaging and product design alternatives. To ensure their products meet these standards, companies can rely on professional package testing services from accredited laboratories, delivering a safe and satisfying experience. 

DES provides package testing services to the medical device, electronic, automotive, and aerospace industries within their environmentally controlled, accredited laboratory.  Please contact an expert if you have any questions.

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This sounds like an easy shock to carry out because a peak of 35G is low compared to many shocks. However, this is a difficult shock to perform because 50 milliseconds is a long duration. Most typical shock durations are less than 20 milliseconds.

A half sine shock impulse has the shape of a half sine wave. More details can be found elsewhere on our blog, in an article titled “Classical Shock Testing“.

A half sine shock impulse is created when the shock machine table accelerates downward, then impacts a rubber material and changes direction abruptly. This abrupt change in direction causes a rapid velocity change which creates the shock impulse. Different rubber or foam materials are used to create half sine shocks with different magnitude and durations.

Half sine shocks can be performed on Electro Dynamic (ED) Shakers, Drop Tables or Drop Towers or Pneumatic Shock Machines. For this particular shock, DES used its Drop Tower Shock Machine. This machine has large bungee cords to increase its capability.

The required velocity change for a 35G, 50 millisecond duration half sine shock is 430 inches per second. A typical free fall drop table shock machine is only capable of a maximum velocity change of approximately 260 inches per second. A free fall drop machine could not attain a 35G peak, 50 millisecond duration half sine shock.

The addition of large bungee cords is used to create higher shock table velocities. The bungees act like large rubber bands or springs pulling the table downward. Higher shock table velocities can also be used to create higher peak G levels.

The impact material (sometimes called the shock programmer) for the 35G, 50 millisecond duration half sine shock was various density foam rubber pieces that were a total of 10 inches thick. It is a dramatic shock, as seen in the video above. As our customer described it, we are moving the shock table at a very high velocity to hit a bunch of pillows!

A typical plot for this shock impulse is shown below. DES was able to easily obtain both the 35G peak and 50 millisecond duration.

What sets DES apart from other labs is our in-depth experience and technical capability to understand and reproduce the most complicated shock profiles. DES has tested to the most complex shock requirements on products that are used in outer space, rockets, missiles, military environments, etc.

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These repeated temperature changes can result in thermal fatigue and lead to eventual failure after many thermal cycles. Accelerated life testing can be performed by cycling the product to high and low temperatures that exceed its normal use temperatures.

It should be noted that temperature cycling may also be referred to as thermal cycling or thermal shock testing.  However, some test standards, such as MIL-STD-883, make the distinction between temperature cycling being performed as air to air testing and thermal shock being performed with the samples transferred between liquids. This article deals with testing performed using an air to air thermal cycle chamber.

Typical temperature cycling equipment consists of at least one hot chamber and one cold chamber. The test samples are automatically transferred between the two chambers by an elevator-type mechanism. It is also possible to perform temperature cycling in a single compartment chamber where the temperature is ramped between hot and cold. This generally produces a slower rate of temperature change compared to the two chamber method.

The acceleration factor resulting from the temperature cycle test is the ratio of the product life at normal operating conditions to the life at accelerated test conditions and is given by the Coffin-Manson equation:

AF = (ΔT _test / ΔT _use) ^m

                        AF = Acceleration Factor

ΔT _test = Test temperature difference (°C)

ΔT _use = Use temperature difference (°C)

m = Fatigue or Coffin-Manson exponent

As an example, assume a product that undergoes 5 daily temperature transitions from
20 °C to 60 °C (ΔT _use = 40 °C) while it is normally being used. The following acceleration will occur if the product is temperature cycle tested using a high temperature of 100 °C and a low temperature of -20 °C (ΔT _test = 120 °C), assuming a typical Coffin-Manson exponent of 3:

AF = (120 / 40)³ =27

Testing this product for 1000 temperature cycles using the accelerated conditions would therefore be equal to 15 years of life based on the stated use conditions.

(27 X 1000 cycles) / ((5 cycles per day) (365 days per year)) = 14.8 years

However, care must be taken when choosing the test conditions so that both the upper and lower temperatures used do not exceed the temperature limits of the product. Doing so can result in failure modes that would not occur during normal operating conditions.

The rate of change between the cold and hot temperatures should also be controlled. Some specifications require that the test specimen reaches the dwell temperature within a given time limit for each change in temperature.

The proper dwell time at temperature extreme must also be considered. In general, the time must be long enough to allow the part to equilibrate to the air temperature. Larger and heavier parts with a higher thermal mass will therefore need longer dwell times than lighter and smaller parts with less thermal mass.

It is also important not to remain at the dwell temperatures for too long of a time, as this can also result in invalid failure modes. An example of this would be solder creep failure in a circuit board that is soaked for too long of a time at a temperature too close to the melting point of the solder.

Knowing the correct value for the fatigue or Coffin-Manson exponent is also important, as small changes in this exponent can have larger changes in the acceleration factor. Exponents for many materials have been reported, and can be found in the literature or on the Internet. It is also possible to experimentally determine the fatigue exponent by performing multiple tests with different values of ΔT _test.

Delserro Engineering Solutions, Inc. (DES) has many years of experience performing temperature cycle testing and can assist customers in setting up a test using the proper test conditions and correlating the results to time in the field.

So if you don’t know what test conditions you should use, what specification to choose, or how to correlate your test to field life, we can help you, because we are reliability testing experts!

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Pyroshocks are unique shocks that have high G-level, high frequency content with very little velocity and displacement change during the shock. The frequency range of a pyroshock is usually 100 Hz to 10,000 Hz or greater. Pyroshocks have a very short duration of usually less than 20 milliseconds. The acceleration time history of a pyroshock approximates a combination of decaying sinusoids as shown in Figure 1.

Pyroshock rarely causes failures in structural members. Typical failures include mechanical relay or crystal oscillator chatter, failures of small circuit board components and dislodging of solder balls which cause short circuits.

The following definitions are from MIL-STD-810G, Method 517, but vary among different pyroshock standards.

Near-field Pyroshock: Maximum frequencies greater than 10,000 Hz and peak amplitudes greater than 10,000 G’s.

Mid-field Pyroshock: Maximum frequencies between 3,000 Hz to 10,000 Hz and peak amplitudes less than 10,000 G’s.

Far-field Pyroshock: Maximum frequencies less than 3,000 Hz and peak amplitudes less than 1,000 G’s.

There is a lack of analytical techniques available to predict a product’s response to a pyroshock. Thus manufacturers must rely on pyroshock testing to qualify their products. Pyroshock testing can be performed using explosive charges or by high energy short duration mechanical impacts. DES uses a Mechanical Impulse Pyroshock Simulator (MIPS) shown in Figure 2 to perform most pyroshock testing. However far-field pyroshock is sometimes completed on our electro-dynamic shakers. DES’s pyroshock equipment capabilities include:

• Mid-field pyroshock with Mechanical Impulse Pyroshock Simulator (MIPS)
• Far-field pyroshock with Electro-Dynamic Shaker or MIPS Simulator
• Frequency control up to 10,000 Hz
• Shock Response Spectrum (SRS) analysis
• Modern high speed sigma-delta data acquisition with numerous channels

Shock Response Spectrum (SRS) analysis is used to measure the acceleration as a function of frequency and the total energy of the applied shock pulse. The SRS is a curve that represents the response of many damped single degree-of-freedom oscillators to a shock pulse. The damped oscillators are tuned to specific octave or frequency bands. A SRS analysis of a pyroshock completed by DES is shown in Figure 3.

DES has successfully performed pyroshock tests on many electronic products that are used in outer space, rockets, and missiles. DES MIPS table has many adjustments to allow for repeatability and shaping of the shock pulses. It is also grounded for ESD sensitive products. Some size and weight ranges for products that we have tested include:

• Size range from less than a 2” x 2” footprint to greater than a 25” x 20” footprint
• Weight range from ounces to 50 pounds

To watch a pyroshock test be performed on our MIPS table, visit our YouTube channel.

Our experienced engineers understand the need for proper selection of the accelerometers along with the setup of the high speed data acquisition system. We have performed an anti-aliasing study on our data acquisition system to prove that it is capable of the demanding requirements for pyroshock measurements without aliasing. This study is available upon request. Please contact DES to learn more about our pyroshock testing and other shock testing capabilities.

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Highly Accelerated Life Testing Procedures

Speeding up the process of device or circuit failure requires extreme inputs, those that are unlikely to occur during real-world use by customers regardless of the environment. Three common testing inputs are high and low temperatures, rapid cycling of the same and vibration along six-axes. In some cases, a highly accelerated life test (HALT) will incorporate combined temperature and vibration stresses. These inputs can result in component failure in the span of days, hours, or even minutes compared to months or years of typical usage.

Benefits of HALT Testing

While the percentages of failure based on the stress applied to a product can vary significantly, highly accelerated life testing can typically expose weaknesses faster than other means of testing. For example, of the above inputs, roughly two-thirds of failures will only come after the introduction of vibration alone or combined vibration and temperature tests. This means that during the product development process, a significant number of potential flaws would not be identified through testing that did not include these two stresses.

Just as important, many of the failures highlighted during a HALT test arise from design problems that are relatively easy to remedy. With thermal-based malfunctions, engineers may find that the issues come from materials with vastly different rates of thermal expansion, or deficient leads or crimps. Other problems can come from flaws in the design of the printed circuit boards.

Combined vibration and temperature during HALT testing can also identify issues related to poorly soldered joints and leads. However, failures during vibration may also be caused by fretting, as well as occurring from adjacent parts coming into contact. These design flaws are relatively simple to identify, such as wires rubbing against PCBs or other sharp-edged portions of the system, and arise regularly during the vibration phase of a HALT test.

As a result of the HALT test uncovering these issues early in the process, or soon after the prototype phase, there is the ability to make relatively small changes in design or production. Companies can also identify parts that may not last even during the warranty period in the fraction of the time it might take to find out during normal lifetime testing. As a result, some clients have been able to save a great deal on their product development costs by identifying part and component weaknesses long before the production process.

Some Facts and Misconceptions about Highly Accelerated Life Testing

• Producing failures is the goal of HALT testing. The user should not necessarily focus on what level of stress caused the problem, but should focus on improving the weak points in their product.
• By applying a sequence of stepped low-temperature soaks, high-temperature soaks, rapid temperature transitions, high G random vibrations, and combinations of these testing modes, the HALT Operational Limit and HALT Destruct Limit of the products under test can be determined.
• The stress levels in HALT are typically far beyond those experienced by the product in its normal operating environment. These higher-than-normal stresses accelerate the time to failure and precipitate defects more rapidly than under actual service conditions.
• The unit is in operation during the testing program and is continuously monitored for operational failures.
• As stress-induced failures occur, the cause shall be determined, and if possible, the component should be repaired so that the testing program can continue.
• Stresses shall be increased until the practical limits of the test parameters have been reached. Examples of practical limits include the melting temperature of solder joints or excessive softening of plastics.
• One common misconception is that an abundance of failures will occur during every HALT. Numerous failures will typically occur, but a large quantity of failures is not likely unless the product is very different than any manufactured before. Successful companies produce pretty good products; otherwise they would be out of business. However there may be a weakness or two in a new product that could create early failures resulting in large warranty costs. These weaknesses should be found in a properly run HALT test.
• HALT is a qualitative test with the goal being to expose design weaknesses. The HALT will not demonstrate a service life or a mean time between failures (MTBF). Other reliability methods may be a better fit to predict an MTBF or service life.

Contact DE Solutions

Delserro Engineering Solutions provides a variety of testing services, not the least of which is highly accelerated life testing (HALT). However, we can also test products in a variety of environments such as vibration, shock, and climatic. We can also design custom reliability test procedures.

If you are looking to find weak points in a design through testing, please contact us for a plan that best suits your needs. Fill out the short contact form at the link above or call us at (610) 253-6637 for a review of your needs. We look forward to working with you to maximize the return on your testing and design investments.

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Real world vibrations are usually of the random type. Vibrations from automobiles, aircraft, rockets are all random. A random vibration test can be correlated to a service life if the field vibrations are known. Since random vibration contains all frequencies simultaneously, all product resonances will be excited together which could be worse than exciting them individually as in sine testing. Sometimes random vibrations are mixed with sine vibrations in Sine-on-Random Vibration Testing. Also, a low level of broad band random vibration can be mixed with additional high levels of narrow band random vibrations in Random-on-Random Vibration Testing.

Some common test standards that have specifications for Random Vibration Testing are:

• ASTM D4169 Standard Practice for Performance Testing of Shipping Containers and Systems
• ASTM D4728 Standard Test Method for Random Vibration Testing of Shipping Containers
• GMW 3172 General Motors Specification for Electrical/Electronic Components – Environmental/Durability
• IEC 60068-2-64 Environmental testing Part 2-64: Tests Fh: Vibration, Broadband Random and Guidance
• ISTA 2A and 3A Procedures for Testing Packaged Products
• MIL-STD-202 Department of Defense Test Method Standard for Electronic and Electrical Component Parts
• MIL-STD-810 Department of Defense Test Method Standard for Environmental Engineering Considerations and Laboratory Tests
• MIL-STD-883 Department of Defense Test Method Standard for Microcircuits
• RTCA DO-160 Environmental Conditions and Test Procedures for Airborne Equipment
• SAE J1455 Recommended Environmental Practices for Electronic Equipment Design in Heavy-Duty Vehicle Applications

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See Sinusoidal Vibration Basics to learn more about vibration fundamentals.

See Sinusoidal Vibration Testing to learn more about the different types of sinusoidal vibration testing.

Examples of vibration test videos can be found on our YouTube page.

Sinusoidal or Sine Vibration Testing

Sinusoidal or Sine Vibration has the shape of a sine wave as seen in Figure 1.  The parameters used to define sinusoidal vibration testing are amplitude (usually acceleration or displacement), frequency, sweep rate and number of sweeps.

A typical sinusoidal vibration test profile is shown in Figure 2.  The amplitude is defined over a range of frequencies.  The amplitude can be constant or variable.  During a sine vibration test, the vibration wave forms are swept through a range of frequencies, however they are of discrete amplitude, frequency and phase at any instant in time.  An important note is that the displacement increases as the frequency decreases for a given acceleration.  At low frequencies, the displacement could exceed the limits of the test equipment.  That is why some specifications use displacement for amplitude in the low frequency range.

Sine vibration is not usually found in the real world unless your product is attached to equipment such as a motor or reciprocating compressor running at a fixed frequency.  Why is it done?  It is good to find resonances (amplitude magnification in the device under test), it is a simple motion and it also produces a constant acceleration vs. frequency.  Also, it is probably carried over from old test methods prior to digital computer controllers.  However sine vibration does not correlate to a field life unless the product is exposed only to fixed frequencies over its life.

Some parameters and definitions of a sine vibration test are:

Amplitude:  The amplitude for a sine vibration test is usually specified as displacement or acceleration.  In DES’s experience, velocity is rarely used in a specification.  As seen in Figure 1, amplitude can be expressed as peak or peak-to-peak.  When displacement is used to define amplitude, it is defined in either peak units of inSA (mmSA) or peak-to-peak units of inDA (mmDA).  SA stands for Single Amplitude (peak) and DA stands for Double Amplitude (peak-to-peak).  When acceleration is used to define amplitude, its units are usually G’s or millimeter per second squared (mm/sec^2) or meter per second squared (m/sec^2).

Frequency:  Frequency is defined as cycles per second.  Its’ units are Hertz (Hz).  Frequency is equal to the reciprocal of the period.

G:  One G is equal to the acceleration produced by earth’s gravity and is equal to 386.1 inches/sec^2 or 9.8 m/sec^2.

Octave:  The interval between one frequency and another differing by 2:1.

Period:  The time it takes to complete 1 cycle.  Its’ units are seconds.  Period is not typically used in the definition of a sine test.  It is listed here because of its relation to frequency.  Period is the reciprocal of the frequency.

Resonance:  A frequency at which an amplitude magnification occurs in the device under test when compared to the vibration table amplitude.  Usually a resonance is defined as a 2:1 or greater magnification.

Sweep and Sweep Cycles:  A sweep is defined as a traverse from one frequency to another.  A sweep cycle varies from one frequency to another and then back to the staring frequency.  For instance in Figure 2, a sweep could be a traverse from either 5 to 500 Hz or from 500 to 5 Hz.  A sweep cycle would traverse from 5 Hz to 500 Hz, then traverse back to 5 Hz.  Some specifications require sweeps while others require sweep cycles which causes confusion.

Sweep Rate:  The rate at which the frequency range is traversed.  The units for sweep rate are usually Octave/minute or Hz/minute.  Octave per minute is a logarithmic sweep rate while Hz/minute is a linear sweep rate.

Random Vibration Testing

Random Vibration is a varying waveform.  It’s intensity is defined using a Power Spectral Density (PSD) spectrum.  Whereas sinusoidal vibration occurs at distinct frequencies, random vibration contains all frequencies simultaneously.  Also phase changes occur over time with random vibration.  Sine and random vibration testing cannot be equated.

Real world vibrations are usually of the random type.  Vibrations from automobiles, aircraft, rockets are all random.  A random vibration test can be correlated to a service life if the field vibrations are known.  Since random vibration contains all frequencies simultaneously, all product resonances will be excited simultaneously which could be worse than exciting them individually as in sine testing.

A typical random vibration test PSD is shown in Figure 3.  The PSD is defined over a range of frequencies.  The square root of the area under the PSD curves yields the Grms.  Specifying Grms only is not sufficient because a wide variety of spectra can result in the same Grms.

Some parameters and definitions of a random vibration test are:

Averages:  Since random vibration constantly changes over time (that is why it is called random), the controller takes samples or snap shots of the vibration data over time.  Successive samples are averaged.  The averaging occurs in each band of resolution.

Average Weighting Factor:  An exponential weighting factor that defines how fast the controller reacts to changes.  The controller reacts faster for small weighting factors vs. slower for larger weighting factors.

Statistical Degrees Of Freedom (SDOF):  The number of independent values (measurements) used to obtain a PSD estimate at a particular frequency.  A higher SDOF means that more measurements are taken.

• For a measurement channel, SDOF = 2*K,
• For control channels, SDOF = 2*K*(2*N – 1) * n.
• K = Number of averages per control loop
• N = Averaging weighting factor
• n = Number of control channels

Grms:  Grms is used to define the overall energy or acceleration level of random vibration.  Grms (root-mean-square) is calculated by taking the square root of the area under the PSD curve.

Kurtosis:  Fourth moment of the Probability Density Function (PDF).  It measures the high G content of the signal.  The kurtosis of a Gaussian PDF is 3.

Number of Lines:  The frequency range of the test divided by the band resolution equals the Number of Lines.  The vibration controller or spectrum analyzer will perform its calculations for each narrow band.

Open Loop/Closed Loop:  Closed loop means the controller will continuously adjust the drive signal to account for changes in the response of the device under test that are fed back from the control accelerometers.  Open loop means the drive signal will be fixed or the controller will stop adjusting the drive signal regardless of changes in the response of the device under test.

PDF:  A statistical Probability Density Function.  A histogram showing the probability of occurrence and the distribution of data.

Power Spectral Density (PSD) or Acceleration Spectral Density (ASD):  Defines the intensity of the random vibration signal vs. frequency.  Its units are usually G^2/Hz or (m/s^2)^2/Hz.

Sigma (σ) & Sigma Clipping:  Sigma is the standard deviation of a statistical PDF.  A Gaussian PDF distribution is assumed for random vibration which takes the shape of a bell shaped curve.  Since the amplitude or intensity of the random vibration will change over time, the time spent at different amplitude excursions is measured using a PDF.  Figure 4 shows a Gaussian PDF.  The vertical axis would be 1/G, the horizontal axis would be sigma and µ is the mean which is equal to zero for a shaker control.  For a Gaussian distribution, 68.2% of the peak G excursions occur between ± 1 sigma, 95.4% between ± 2 sigma, 99.7% between ± 3 sigma.

Vibration controllers allow you to clip peak amplitude excursions using Sigma Clipping.  Many specifications allow the clipping to be set at ± 3 sigma.

Frequency, G, octave, period and resonance are the same as defined under sinusoidal testing.

For more information on Vibration Shock Testing or other testing services contact DES or call 610.253.6637.

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HALT and HASS can accelerate a product’s aging process from actual months into test minutes much faster than traditional testing!

What is HALT?

HALT – Highly Accelerated Life Testing

HALT is used to find product design weaknesses making the product more rugged.

• HALT is typically done during Design.  It is destructive!
• Stresses are applied in steps to find a product’s weaknesses, operational design margins, and destruct limits.
• Stresses are higher than normal to obtain time compression and accelerate aging.
• HALT is not a pass/fail test.  It is pro-active!  The stresses are increased until the product fails, rather than testing to predefined limits.
• All HALT failures represent an opportunity for improvement and may show up in the field.
• Many failures are easy and inexpensive to fix.
• HALT typically takes 3 to 5 days.

What is HASS?

HASS – Highly Accelerated Stress Screening

HASS is used to find defects and flaws in production to monitor the quality and consistency of your manufacturing processes.

• HASS is done during Manufacturing.
• HASS is a screening method used to expose manufacturing process problems that would cause a failure in normal field environments including shipping, storage and use.
• Stresses may be higher than normal operation to precipitate defects in a short amount of time.  HASS stresses are typically higher than traditional Environmental Stress Screening (ESS).
• Types of stresses used are similar to those used in HALT.
• HASS screens take typically from an hour to a few hours.
• HALT must be performed before HASS.
• Safety of Screen (SOS) is used to validate the screen proving that sufficient life is left for a normal use lifetime.

Reasons to Use HALT/HASS

• To produce a rugged, reliable product.
• Products have many electronic parts subjected to combined high/low temperature and vibration loads.  Many parts are not tested for these combined loads.
• With thousands of electronic components present, a failure of a single component could cause the entire system to fail.  This will lead to warranty and engineering redesign costs, and unhappy customers.
• To find and understand the operating limits of your products.
• To find and understand the destruct limits of your products.
• To compare different electronic components and suppliers (Evaluation of Competing Vendors).
• To regularly audit or screen your production components to check for and improve manufacturing quality.

Typical Stresses Used in HALT and HASS Testing

• Vibration applied over a broad frequency range (6 DOF, 60 Grms, Random vibration energy to 10,000 Hz)
• Temperatures (-100°C to +200°C)
• High temperature rate of change (60°C / minute)
• Electrical loads
• More stresses (fluid pressure and viscosity, pH, unbalance, geometry, etc.)
• Combination of all loads

Typical HALT Profile

Why Products Fail

Every product has a statistical strength distribution. Failures will occur where the Product Strength and Field Stress Curves overlap shown in red.  HALT/HASS will force the weaker components to fail in the chamber.  HALT and HASS will shift the Product Strength curve to the right.  The goal of HALT/HASS is to produce a large design margin or gap between the 2 curves, resulting in less field failures and a more reliable product!

Benefits of HALT

• Shorter design cycle = Quicker Time to Market.
• Reduced design cost.
• Usually less expensive, faster, and more effective than traditional pass/fail testing.
• Find and improve design margins.
• Produce a more rugged/reliable product with less field failures and warranty expenses.
• Reliable products lead to happy customers.
• Happy customers lead to increased profits/market share.
• ROI’s in the thousands or greater are being reported.

Benefits of HASS

• HASS screens are shorter than traditional methods (ESS).
• Reduced time and cost to screen production.
• Finds defects sooner and correct problems faster.
• Fewer defects reach the customers hands.
• Improved product quality and manufacturing process control.

DES reliability testing can help you in all phases of your project.

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