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Random

Simulate random vibration reflective of the real world

Gain a comprehensive understanding of a product’s response to the vibrations it will encounter in its environment of use. With up to 26,000 lines of control, Random provides the highest possible control in an easy-to-use format. Analyze random data with a comprehensive suite of graph display options or generate a test from recorded data with our advanced test development options.

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VR9200

Up to 26,000 Lines of Control

VR controllers come standard with 50 to 26,000 lines of control to meet your test’s required frequency resolution. The standard frequency range is DC-4,900Hz, which can be extended up to 50,000Hz with the VR9203 High-Frequency option.

Easy Test Entry

  • Random Test Settings Breakpoints ScreenshotEnter frequency or amplitude breakpoints in an easy-to-read, tabular format. VibrationVIEW supports over 9,999 breakpoints, suitable for virtually any test specification.
  • Control constant or ramped acceleration, velocity, or displacement.
  • Automatically calculate the frequency of the intersection between any constant acceleration, velocity, or displacement.

Input Configuration

Use one input channel for control or configure up to 512 input channels with multi-channel averaging or multi-channel notching. You can enable individual channel tolerances for spectrum and RMS limits.

One to 4 control loops can be run simultaneously to control up to four shakers independently with four individually configurable and statistically independent waveforms.

VibrationVIEW screenshot with Microsoft Excel

Independent Channel Notching Profiles

Assign maximum limiting breakpoint profiles to individual channels. If necessary, the drive output will be notched to keep the channel’s input spectrum below the defined profile. Each channel can support up to 9,999 breakpoints, or the limit can be a dB level relative to the demand profile.

You can also define minimum limits to boost the drive output if a channel is below a defined profile. The notching profiles may also be used as spectrum abort limits, and the abort limit breakpoint profiles can be assigned to each individual channel. If the channel reaches the defined limit, the test will safely shut down.

Test and Level Scheduling

  • Tests can be scheduled to run a user-defined length of time.
  • Spectrum levels can be scaled by a specified dB-level, percentage, or for a specified RMS acceleration.
  • Level schedules can run for various durations at different acceleration levels.
  • Levels can be changed while the test is running.

Part number 9200

VR9100

Random Graph Display Options

Available graph display options include power/acceleration spectral density (PSD), scatter plot, and kurtosis versus time.

Graphs can be easily auto-scaled, and the cursor display can be adjusted. Data and text annotations can be easily placed on the graphs, and data values update live with changes.

VibrationVIEW Random test data screenshot

Advanced Testing Options

Random Import (Optional) VR9204

Import analog or digital time data to automatically generate a random profile. Import PSD data to analyze statistics from a time-history recording.

Fatigue Damage Spectrum (Optional) VR9209

Measure a product’s fatigue and calculate its lifespan. For years, engineers have used methods to calculate the lifespan of a product based on the material s/n curve. With FDS, rain flow analysis techniques are applied to measured vibration, equivalent fatigue is quantified, and time to failure is calculated. Commonly used life acceleration techniques are applied to shorten test time.

Dual Phased Output (Optional) VR92-RDP

Perform dual-axis testing with phase control. The drive and the aux (COLA) output are used to drive different shakers with the same profile. The matched phase between the two outputs is auto-controlled.

What is Random Vibration Testing?

Real-world vibration is inherently random. A random vibration test, then, is a realistic method of bringing a product to failure. A random test excites all frequencies in a defined spectrum at any given time. By exciting all the resonances of the device under test, engineers can determine the interaction between multiple resonances.

Read the full paper here.

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When Should I Select a Random Test?

A random vibration test can be generated to represent one or multiple operational environments. It can also be accelerated to represent a lifetime of damage that can be run in a lab.

A random vibration test excites all the frequencies of the device under test and is a realistic representation of the operational environment. By exciting all potential resonances at the same time, a random vibration test reveals the interaction between multiple resonances. It often reflects a greater damage potential than a sine test.

Select a random vibration test when:

    • Testing a product against vibrations that will occur in the field environment
    • Determining how a product will respond to the excitement of multiple resonances at the same time
    • Testing a product to failure

Short-Duration Random Testing

VibrationVIEW screenshot showing Acceleration Spectral Density with and without iDOF

Testing facilities in industries such as aerospace often test high-value equipment at extremely high levels of random vibration for a brief period. The goal is to run a realistic test that will identify any reliability issues without damaging the equipment.

Ideally, the test engineers want to see a smooth control trace on the PSD that remains within an established tolerance range. Short duration random vibration tests typically have very tight tolerances (±1.5dB). The statistics of averaging FFT power values limit the possibility that all lines will be within tolerance in a short timeframe.

Instant Degrees of Freedom® (iDOF) calculations are a statistically valid way to provide smooth lines and an in-tolerance PSD in a brief testing period.

iDOF Software

What is the Power Spectral Density (PSD)?

VRU Random Vibration Testing Course

Random vibration is often analyzed with the power spectral density (PSD). The PSD represents the distribution of a signal over a defined frequency spectrum. It reveals resonances and harmonics that may not be visible in a time-history graph.

Normally distributed time-domain data is transformed into frequency-domain data using the fast Fourier transform. An understanding of the PSD will help engineers to determine the correct parameters to use when generating a PSD from a waveform. To learn more about generating a PSD, please enroll in our Random Testing course on VRU.

What is the Probability Density Function (PDF)?

The probability density function (PDF) is another method of quantifying random vibration from a digitized signal. It is a histogram that is computed by counting the number of samples within a set of frequency bins, which cover the range of the signal’s amplitude.

The PDF has a Gaussian, or normal, distribution. A normal distribution has a skewness of zero and a kurtosis of 3. The area under the PDF curve is equal to one.

What is Kurtosis?

Kurtosis is a dimensionless measurement pertaining to the average deviation of a signal from its mean value. Present-day random testing assumes Gaussian distribution of random data and, therefore, a kurtosis value of 3. However, there are data that do not fit the Gaussian distribution. In such instances, a kurtosis value of 3 may omit higher peak values and result in under-testing.

Vibration Research recommends using kurtosis control in some testing situations to produce a more realistic random test. Learn more about our kurtosis control innovation Kurtosion.

Read also: Kurtosis – the Missing Dashboard Knob

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