FFT made easy!
What is FFT?
Fast Fourier Transform (FFT) is a measurement technique that gives narrow-band filtering using post-processing of a digital time record. Modern digital processors can repeat the analysis fast enough to provide real-time measurement (all samples are represented equally in the results, i.e., no data is lost because of calculation dead time).
FFT provides a constant bandwidth spectrum extending from 0.1Hz to 20kHz (in the case of 2260 Investigator™), characterised by the number of frequency bands (called FFT lines).
Type 2260 has over 400 lines, with a resolution better than 50Hz.
To increase resolution, the frequency span can be reduced by factors of 2, thereby improving resolution by factors of 2. As an example, with a 0.1 - 313Hz span, the resolution is better than 1Hz. The same high resolution can be selected around any particular frequency - called zoom.
Who Needs Narrow-band Filtering?
In the acoustics community, 1/3-octaves are satisfactory for most frequency analysis, while octave bands suffice for applications such as room acoustics and environmental noise. However, for analysing noise that includes annoying tones, narrow-band FFT filtering is often preferred. Machinery tends to have vibration modes (and noise) with narrow peaks, or vibration and noise with repetitive patterns. Therefore, the FFT analyzer is a valuable tool for the troubleshooter or developer of machinery.
Why FFT on Investigator 2260?
FFT is a standard feature of advanced vibration analyzers, and is also found in many simple vibration meters. But we believe that many 2260 Investigator users will enjoy the economy and ease of use of FFT on a familiar instrument. We also believe that the combination of sound and vibration capability will appeal to new users. The features draw on Brüel & Kjær's long experience in FFT for sound and vibration applications.
Features
With the new module, 2260 Investigator becomes a single-channel FFT analyzer, suitable for measuring continuous and transient signals. A flexible internal trigger is provided, as well as an external trigger for transients. To evaluate the tonal content in noise, the software can point out tones and calculate their audibility.
For vibration measurements, the new DeltaTron® Adaptor ZG0423 is available. It accepts DeltaTron accelerometers, and via Charge Converter Type 2646, also accommodates charge accelerometers.
Most importantly, all the functions you need in the field (e.g., frequency span, zoom and cursors) are activated by keys within easy reach.
With Type 2260E, we proved that sound intensity measurement could be made easy. And we believe that the new Type 2260H will be enjoyed just as much in the field of FFT.
Delivery Information
For those who already own a 2260, the FFT module can be ordered as BZ7208. A 2260 Investigator with BZ7208 installed comes as Type 2260H. It includes BZ7210 Basic Sound Analysis software, a microphone preamplifier and microphone. For documentation on features and specifications, please consult the Product Data. Supporting PC software will be available as updates to Noise Explorer™ Type 7815 and Evaluator™ Type 7820.
Product Data: Hand-held FFT System 2260 Investigator and FFT Software BZ7208 - Type 2260H bp1894.pdf
French Version: bp1898.pdf
German Version: bp1897.pdf
Italian Version: bp1905.pdf
Application Note: Tone Assessment using the 2260H Sound Level Analyzer
Bo0499.pdf (size 562 kb)
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