Environmental Stress

Sine Vibration vs. Random Vibration Testing. Which Should You Perform?

When it comes to vibration testing there are two popular types to consider: sine and random. We receive frequent requests for clarification on which test to run specific products on. The answer is, of course, it depends. So here’s a bit of background to help you make a decision.

Sine Vibration Testing

Sine vibration testing applies a single frequency to a test item and selectively excites resonant structures within the device. In a swept sine test a vibration sine tone is ramped up and down through a range of frequencies and for a specified rate and duration. 

Sine testing is primarily useful in identifying resonant conditions within a test item. On an electronic module, the circuit boards are often the main resonant structures and typically their fatigue conditions are most important to understand. However, the components themselves mounted on the PCB as well as the electronics housing also have their own unique natural resonant conditions which are usually different than the circuit boards. Using sine vibration to identify resonant conditions on the PCB or on other test item structures is an effective way to understand how mechanical vibration propagates through a device and can help designers stiffen or dampen elements of the product to reduce the probability of fatigue failure.

Sine vibration test frequency plot (top). Time waveform plot (bottom)

Swept sine testing is also useful when the product’s application environment includes reciprocating equipment like motors, engines, turbines, or fans. If the application vibration environment has a significant sine characteristic and if the field vibration can be measured then a swept sine test covering the recorded environmental conditions can be run for a specified duration and at an increased amplitude to simulate a lifetime of fatigue stress.   

Sine testing is also helpful to simulate worst-case fatigue exposure by programming an electrodynamic vibration input sine tone to line up with the major resonant frequency of the test item. A vibration test that applies a fixed sine dwell at a resonant frequency will usually generate the highest amplitude displacements and accelerations and therefore the most damaging fatigue stress conditions for the product.   

Random Vibration Testing

random vibration test is one comprised of vibration energy at all frequencies over a specified range.  The vibration frequency components that make up the input signal for a random test combine in amplitude and phase to create a time waveform that appears on an oscilloscope as random noise. The characteristics of the random waveform are constantly updating and changing within the bounds of the programmed random input.

Random vibration test frequency plot (top). Time waveform plot (bottom)

Random vibration is the most common type of validation and qualification test that is performed for electronic modules. The majority of vibration environments where devices are mounted, especially electronic devices, are characterized as having predominantly random vibration conditions.   

The most effective vibration test to run is one based on actual field measurements of the specific environment where a product will be operated. By recording the in-situ vibration environment with an accelerometer or multiple accelerometers a random power spectral density plot can be created and run at the level recorded or increased to accelerate fatigue and shorten test time. On a random vibration power spectral density plot, the acceleration amplitude is scaled on the y-axis in units of G2/Hz and the x-axis units in frequency. If the measured vibration environment has sinusoidal characteristics then the random vibration profile can also be tailored to include sine tones applied over the random vibration background.

For both random and sine vibration tests, durable mounting fixtures are critical to a successful test. Elite’s in-house experts apply their expertise to design and fabricate custom fixtures to accurately simulate installed orientation and transmit interference-free vibratory energy.

If your application and project do not afford the option of measuring field vibration conditions, then the following standards provide recommendations for test conditions and durations. Some of the standards are free for download while others are available for download but for a fee.  

Military Standards
MIL-STD-810H (Method 513)
MIL-STD-202 (Methods 201, 204)

STANAG 4370 (AECTP-240, AECTP-400, AECTP-600)

Telecom Equipment Transportation
ETS 300 019-2-0

Electronic Components

Automotive Electronics
ISO 16750-3
GMW 3172

We’ve been running vibration tests at Elite for a long time so if you need assistance in specifying a vibe test for your product contact me to discuss the particular details of your product and your end-use application. With 8 vibration test systems and large item capability, Elite is among the most capable dynamics testing labs in the world to get your project started quickly.

Contact Elite’s experts today to learn more about our Vibration and Shock Testing capabilities and how we can help qualify your products efficiently.

Watch our tutorial to prepare for your next vibration testing project.

Elite Expands its Environmental Test Capabilities…and in a Big Way!

The recent motto around Elite regarding test systems has been… “Go big or go home”,  This certainly applies to our newly commissioned walk-in chamber, mechanical shock machine, and our universal test machine.

New- Walk-In Chamber

With the installation of a new large walk-in chamber, we have increased our biggest climatic test volume fivefold when compared to our previous capability. Our new Thermotron temp-humidity chamber stretches 16ft deep by 11ft wide and 9ft tall and will ramp at change rates of 5C/min between (-67C) and (+85C). It can also control humidity from 95% down to 5% and produce condensing and non-condensing humidity environments as well as frost and ice conditions. The chamber has a reinforced floor for heavy systems and is fitted with three 6-inch diameter access ports and electrical feedthroughs, plus it has two large viewing windows.  

With twin 30hp compressor sets for refrigeration cooling and 72kW of heating elements, Elite test engineers are ready for the largest and most complex types of products and tests that clients can send our way.

New-  Mechanical Shock System

We’ve upgraded our mechanical shock capabilities with a fully automated pneumatic shock table from Vibration & Shock Technologies (VST).  This machine is designed to produce half-sine and sawtooth with far greater amplitudes and a wide range of millisecond durations.  For high G pulses we can reach up to 3000Gs-0.5msec and for long pulse durations, we can extend 100msec (at 10Gs).

The system controller and software will make Elite shock testing more efficient, productive, and cost-effective.  The PC-based controls include preconfigured shock profiles to speed waveshape verification and overall test time. Plus, repetitive shock pulse testing can be programmed for applications that require hundreds or thousands of cumulative pulses.

With this new machine, we have an impressive lineup of shock capabilities, including:

  • Electro-dynamic vibration tables

Our existing ED shakers can produce a wide range of shock pulses in a manner that makes vibration and shock testing quick and efficient. 

  • HALT Synchronized Shock 

Our HALT table can produce “synchronized” shock pulses in excess of 1500gs in single impact or rapid succession (up to 25Hz). 

  • Avco Extreme High-G 

Half-sine shock pulses up to 30,000Gs peak 

  • VST Large Shock Machine

Table size 30” x 30”, payloads up to 1000lbs. 

Shock amplifier to reach 3000g. 

Crash pulses with time durations up to 100msec.

Give Elite a call to discuss your next mechanical shock test requirement. We can bump, hit, drop, or crash products in nearly any way our client request…sounds like fun. 

New-  55kLbs Universal Test Machine

With the addition of a 55klb (245kN) universal material tester from MTS, Elite now has a fleet of five machines to test materials and equipment for a range of properties such as strength, deflection, or fatigue. As the largest of our UTMs, this 55k MTS machine more than doubles our test capacity for tensile and compression applications.

In total, our range of machines includes load cells and frames that can measure high force parameters up to 55klbs for tensile or compressive applications, down to 10N load cells for the most delicate force measurements such as for keypad actuation forces.  

Plus our MTS 370 load frame is fully configurable with a temperature chamber capable of cooling to (-73C) and heating to (+315C). We can perform materials testing at a range of temperature extremes while concurrently applying full load conditions.

The applications for these test machines are wide-ranging. They include traditional types of material property measurements such as yield and ultimate strength, modulus, strain, and deflection. We test connectors and cables to evaluate connector lock and unlock forces, connector/wire crimp holding characteristics, beam deflections, and enclosure crushes. If you need answers to how your device will perform when pulled or pushed, Elite can provide the test systems that provide the data—and with precision.