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What is Resonance ?
irst, in order to explain resonance we have to explain the terms we will use. • A resonance is a particular frequency. • Frequency measures the amount of time it takes to complete one cycle • The number of cycles in one second is the frequency of an oscillation. • Frequency is measured in Hertz, named after the 19th-century German physicist Heinrich Rudolf Hertz • A single Hertz is equal to one cycle per second. n technical terms, resonance is the tendency of a structure or material to oscillate at maximum amplitude at a certain frequency. This frequency
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is known as the structure’s resonant frequency. A dictionary gives us - the state of a system in which an abnormally large vibration is produced in response to an external stimulus, occurring when the frequency of the stimulus is the same, or nearly the same, as the natural vibration frequency of the system.” When damping is small, the resonant frequency is approximately equal to the natural frequency of the structure, which is the frequency of free vibrations of the molecules of the material itself. urt er, resonance s t e con t on w en t e natura frequency of a structure or material and the frequency at which it is operated are equal or very nearly equal. This makes the structure or material become very excited; this is the classical resonance state. This resonance state can often lead to unexpected behaviour of the structure or material. The natural frequency, often called the fundamental frequency, is related to the size of the structure and the material it is made of. This is because the larger the structure the lower the frequency and therefore
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What is Resonance ?
Figure 2
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What is Resonance ? a larger waveform can exist inside the structure or material. The natural frequency is also related to he speed the waveform can propagate through the structure. This is determined largely by the molecular make up of the material. Gas, for example, has many free molecules with high kinetic energy, so the waveform can move quickly through the material. A solid has much fewer free molecules and is much denser, therefore the waveform moves much more slowly. n order to measure the resonance of a structure or material with a Prosig P8000 data acquisition system and DATS Professional signal processing software it is necessary to attac an acce erometer to t e structure. t is then required to exert or stimulate the structure with the frequencies that it is normally exposed to in its working life. For example, an automotive car yre would need to be subject to the frequencies it would encounter whilst in use. This would normally be accomplished by use of a shaker or a large heavy hammer. The tyre for example would need to be tested in isolation, whilst not connected to anything else like he vehicle suspension or wheel rim as these other parts would have their own resonant frequencies and would make the capture and analysis of the tyre resonant frequency difficult. he measured response from the accelerometer will be relative to the excitation. The excitation must be an acceptable representation of the normal working requencies applied to the structure or material. If this structure has a resonance in this frequency range there will be a large peak. This large peak is the resonant requency of the structure or material. If no peak is detected then the resonant frequency is outside the operating range of the structure or material. In order o find the resonant frequency of the structure or material it is then required to apply a wider range of requency excitation until the resonance is found.
Figure 2 shows a frequency spectrum, this spectrum as in Figure 1 shows a frequency response. However, Figure 2 shows, using cursors, the exact frequency of the resonance. In this case the resonant frequency is 245 Hz. This means that this structure should probably not be used if in its working life it will be exposed to this frequency. Figure 2 also shows that if this structure was to e use , an on y expose to z to Hz or perhaps 0Hz to 200Hz , its resonant frequency would not be excited. And therefore the structure would behave as expected.
James Wren James Wren is Sales Manager and an Application Engineer for Prosig Limited. James graduated from Portsmouth University in 2001, with a Masters degree n ec ron c ngneer ng. e s a mem er of the Institute of Electronic Engineers. He as een nv o v e w mo or spor r om a very early age with special interest in data acquisition. James is a founder member of the Dalmeny Racing team.
ros g prov e a a acqu s on, noise & vibration, acoustic, ea con on mon or ng an refinement solutions for the scientific and engineering communities and offer a number of standard hardware and software products. Take a look at www.prosig.com to discover why major automotive, military, aerospace, power and industrial companies rely on Prosig for their complete data acquisition, signal analysis and reporting software & ar war e.
igure 1 shows a frequency spectrum, this spectrum is a response of a structure to its excitation. A large spike can clearly be seen at approximately 250 Hz.
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DATS™ Professional software (01-55-622) • Acquisition, analysis & reporting • Wide range of analysis functions • Automated processing through worksheets & scripts • Built-in report generator (Intaglio)
• Comprehensive QA features The DATS software package contains all of the measurement and analysis tools needed in an engineering or research environment. Data acquisition software comes as standard. There is a comprehensive framework of analysis tools (interactive worksheets and scripting). The Intaglio report generator provides template driven, high quality repor s. DATS offers outstanding value both in cost and productivity gains. There are no extra cos s or a a acqus on suppor , anays s scripting or reporting software. And you won’t pay a fortune for support even though we provide a service agreed by many to be the best available. And if you subscribe to our mo es y pr ce suppor serv ce you w be entitled to regular software updates. Many man-years of signal processing expertise have been spent on DATS during its 30 years of development. When you purchase DATS you are buying a share in our knowledge. DATS software has proved itself time and time again in diverse and eman ng app ca ons aroun e wor . DATS is built around a fully published, standard data format. A number of features make the DATS data structure unique:
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• A complete history of any analyses performed is stored with every signal. This provides a complete audit trail from data capture to final result. • The Named Element facility provides for storage of everything from data acquisition settings to results of ana yses.
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• The integrated Project Manager allows a user o con gure an s ore any vara es relevant to a test or project with every signal captured or analyzed for that test. DATS includes a full featured acquisition suite. Capture parameters are easily configured using the setup matrix. During a capture real-time displays show time histories, frequency spectra, numerical levels, gauges, waterfalls and order tracks. Channels can be tagged for immediate analysis and results of this can be viewed immediately after capture. Automatic averaging of multiple runs s nc u e an average runs can be easily reviewed and assessed. As well as a highly interactive mode, DATS can be automated either using the Visual Scripting environment built into the worksheet interface or using the DATS BASIC scripting language. Scripts offer a fully featured Visual BASIC style language. Write your own sequences w a a acqu s on, input & result forms, DATS analysis functions, reporting, signal access unc ons, n egra on w ena e ® applications (Microsoft Office etc) and much more. An important part of most tests or investigations is the final report. DATS includes the Intaglio Report Generator that combines the word processing power of Microsoft® or an e grap ca an analysis capabilities of DATS using OLE technology. Draft reports (templates) are crea e us ng n ag o oo s. ac time a report is required the latest data is added to the draft to produce the final repor . epor s can e e e y e author, but are “locked” when the report is distributed.
Realtime graphical displays during capture a most nstant post capture resu ts
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