Software Makes Good Vibrations Even Better

When shopping for a vibration test system, one of the most important components is the software. It can make the difference between a job done efficiently and easily versus one done crudely and arduously.

Selecting the best software for your vibration test needs begins by determining what functions and characteristics you expect from the software. To help you find the best fit, EE asked some of the experts in vibration test software. They say to look for ease of use, performance, support, safety and report-generation capabilities.

Ease of Use

Ease of use must incorporate a balance of comprehensive capabilities and a relatively simple user interface, said Raymond Boyd, Vice President of Sales for LMS North America. It should include:

o An automatic mode for unskilled users.

o An interactive menu for technicians.

o An advanced menu for engineers.

o An interactive adviser for newcomers.

o A user-defined menu function.

Look for simple tools and common functionality throughout the software because it is imperative to run tests and analyze data quickly and efficiently, said John Raymond, Application Engineer for Unholtz-Dickie. You must have confidence that you can run a test without spending hours reviewing manuals, referring to notes or opening layers of pull-down windows. An efficient design provides quick access to the information.

The user interface should offer graphical point-and-click operation with logical, simple menus and test parameter panels to speed test setup, added Dave Galyardt, Product Marketing Manger for Spectral Dynamics. Direct and simultaneous access to all setup panels, including control parameters, transducer channel tables, documentation, data storage options and test schedules, makes it easy for you to change test parameters. Context-sensitive help, on-line help and a uniform interface for all applications reduce training time and simplify operation.

Default setup parameters also help eliminate the need to re-enter or recall routine tests, continued Mr. Galyardt. System tables shared by all applications, such as shaker limits, transducer channel information and interface settings for thermal chamber controllers, do away with repetitive data-entry tasks and increase productivity.

The shaker-limits table, for example, stores the maximum acceleration, velocity and displacement-limit parameters. When a new test is defined, the software compares expected test parameters with shaker parameters, said Mr. Galyardt. These checks are the safety interlocks that protect shakers and amplifiers from damage. If shaker parameters are exceeded, a warning is issued and testing is barred.

The software user interface should facilitate fast, convenient monitoring and control of a test. It must allow simultaneous viewing of multiple data display windows, a test control panel and a status panel, and access all controls by pointing and clicking. These capabilities enable more tests to be performed in less time.

The capability to choose manual or automatic test control is another function to consider, continued Mr. Galyardt. Manual control provides precise supervision for difficult tests. Automatic control frees you for other tasks and offers convenient features such as level scheduling and test scheduling.

Test automation, in conjunction with a remote interface, combines vibration tests with other environmental tests such as temperature, pressure and humidity. For the most efficient operation, the vibration software must be able to communicate its status across the remote interface to other systems via a programmed status message.

A hand-held remote control panel also makes your job easier, said Mr. Galyardt. For example, when you must investigate noise and vibration, you need to be near the test article to hear and observe the problem. It is inconvenient and time-consuming to return to the system console room to adjust the controls each time a test adjustment must be made. A hand-held remote-control panel helps you operate the vibration test and receive status information while at the shaker table.

Performance

Performance is characterized by three main parameters: dynamic range, servo speed and frequency range, said Mr. Raymond. These parameters are easily evaluated for all test types, including sine, random and shock, when dynamic loads are run on a vibration test system. Vibration test software should not be selected without running it under dynamic conditions.

The performance of the system is another aspect that must be evaluated when purchasing vibration test software, observed Mr. Boyd. It must be field expandable from four to 64 parallel channels, and have unlimited scheduling, break points, test setups and on-line traces.

The fundamental capability of a controller and its software to produce the required random, sine, shock and sine-on-random vibrations should be examined critically, said Dr. Sri Welaratna, President of Data Physics. For example, some systems create random vibration by outputting blocks of random waveforms of the required magnitude, but do not deliver the needed spectral density. This design ignores the discontinuities from block to block, he said.

Some controllers produce sine waves that are stepped in frequency as opposed to swept, continued Dr. Welaratna. A sine controller should continuously sweep the sine wave, which is possible only if the phase increment is changed from one sample to the next. If the system does not measure the responses all the time, it will miss the highest response values near resonance and the lowest values near antiresonance.

The vibration test software should also make full use of the data acquisition and output generator hardware, said Mr. Galyardt. The software must optimize the hardware performance for each test application, including random, sine and shock.

Random tests, for example, accomplish this via filters that provide the best out-of-band rejection. Shock tests use software filters that have a linear phase response in the bandwidth of interest.

Advanced control algorithms also are important software functions because they ensure that real-world tests can be run quickly and easily, continued Mr. Galyardt. Another algorithm is the adaptive control type which compensates for nonlinear behavior of the shaker system or test article, ensuring swift, accurate control during difficult tests. Adaptive algorithms help achieve speedy error corrections and good excitation stability because they continuously check the dynamics of the DUT and change the control accordingly.

Support

Support from the supplier is important to consider before purchasing a system, said Mr. Raymond. Developing and supporting a digital control system for the long haul are no trivial matters. It takes a large amount of resources and a firm commitment by a manufacturer to support the vibration test system. Before you select a software package, determine what the company’s long-term reputation is in the industry.

The cost of purchase and ownership should be reasonable, said Dr. Welaratna. It is important that the purchase price be similar to that of other manufacturers with comparable performance and features. Look closely before you buy a software package priced well below other comparable products, he warned. Conversely, realize that high price does not automatically equate to high quality.

Safety

Test safety should not be overlooked. It could mean the difference between testing a product within its appropriate tolerances and accidentally damaging it with too much stress. Make sure the software will never output a signal resulting in an unsafe testing condition.

Verify that the software safety checks used to abort tests are implemented correctly when test levels exceed or fall below tolerance bands, said Dr. Welaratna. These safety checks should be implemented every time out-of-range conditions are experienced.

These seemingly obvious requirements have many subtle aspects to consider, added Dr. Welaratna. For example, low or high rms acceleration in a random test must be measured immediately so the system can abort without averaging the data into the power spectral density measurement. This allows speedy resumption of an aborted test.

Report Generation

A critical aspect of testing is storing test data and documenting results completely, accurately and meaningfully, said Mr. Galyardt. The software should allow you to automatically store data to disk during test and at specified intervals or let you manually save the information.

Ensure that the system has the capability to make reports conveniently, said Dr. Welaratna. The ability to generate reports to your needs rather than those created in the image of the manufacturer is essential. It can result in tremendous savings in time.

After each test, the software should automatically produce a complete post-test summary, including alarm and abort status, date, time and test level, said Mr. Galyardt. This summary is useful for reporting and certifying tests. Finally, the software should be capable to convert binary data files into ASCII data files, making it simple to import the data into general-purpose data-reduction programs and spreadsheets.

Vibration Test Products

Vibration Controller Features

Software Modules

The DP550Win Vibration Controller provides modular software for all modes of vibration and shock control. The controller is available in a DOS-based and a Windows 95-based configuration. Both versions offer resolution to 1,600 lines for random, sine-on-random and random-on-random functions. An advanced sine-on-random function offers 10 independent tones with separate profiles, sweep rates and directions. A random-on-random function provides 10 independent narrowbands with separate profiles, sweep rates and directions. Data Physics, (408) 371-7100.

Digital Vibration Controller

Is Windows-Based

The Sigma Series Digital Vibration Controller provides random, sine, SRS and shock-testing capabilities in a Windows-based environment. It controls eight shakers independently and manages eight accelerometers simultaneously. Random vibration control offers 1,600 lines of resolution. Sine and random frequency ranges from 1 Hz to 5 kHz. The software operates the Sigma 500, Sigma 1000 and Sigma 2000 systems. Environmental Screening Technology, (616) 772-5485.

Vibration Software Uses

Touchscreen Interface

TouchTest Sine and Random Vibration Software provides the capability to access test, monitor, save, document and analyze functions through a touch-screen interface. The controls adapt to most hydraulic and electro-dynamic vibration systems. An interactive color touchscreen provides fully annotated, real-time displays of test conditions. System features include closed-loop sine and random vibration, random test queue, random demand profile, automatic sine dwell sequencing and automatic start and stop of hydraulic power supply. Lansmont, (800) LANSMON.

Vibration Control System Meets

MIL-STD-810 Requirements

The CADA-X Vibration Control System meets the environmental testing standards of MIL-STD-810. Version 3.3 enables you to monitor test status from any system on the network. It features sine control with programmable compression speeds and sweep rate changes. Chamber control and functionality testing can be programmed and software modules can be tailored to specific applications. A data base allows access to data sets, transducer libraries and shaker-performance envelopes. The system provides plots to fit an existing lab format. LMS North America, (810) 952-5664.

System Enables

Testing in Parallel

The VCP9000 Control System can run a random program, set up a sine program, plot test data and synthesize a shock response spectrum in parallel. It is based on Hewlett-Packard hardware and the X-Windows operating system. The system provides up to 64 input channels for random, swept and fixed sine, classical shock, sine-on-random, random-on-random and sine-on-random-on random control. The frequency ranges from 50 Hz to 12,800 Hz. Resolution extends from 100 to 3,200 lines. Data analysis and plotting functions include automatic peak markers, integration, differentiation, power spectral density and waterfall graphics. M+P International, (201) 239-3005.

Software Controls

Test Signals

The OUTPUT GENERATOR software allows the 2550 System to generate and output test signals. Half sine, versed sine, sine chirp, burst random, random or fixed sine can be selected from the signal generation library. The output waveform is customized by setting the sample rate, amplitude, pulse duration and coast-time parameters. Sample rates range from 128 S/s to 51,200 S/s. The peak-voltage output level extends from -10 V to +10 V. Spectral Dynamics, (408) 474-1700.

Digital Control System

Supports Parallel Inputs

The UD-VWIN Digital Vibration Control System operates within a Windows™ environment running on a Pentium®-based workstation. The system uses digital signal processing and shaker control algorithms for real-time test control. It supports random, swept/discrete sine, transient, random-on-random and multitone sine-on-random vibration environments. Multichannel parallel inputs, each with 16-bit resolution, are provided. The graphical interface supports eight independently configurable displays. Unholtz-Dickie, (203) 265-3929.

Copyright 1996 Nelson Publishing Inc.

July 1996

 

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