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The demand for quieter vehicles is escalating as consumers want quiet interiors for conversing, speaking on their phones, or listening to music while driving. In many cases, "quietness" can make or break the sales success of products. This in turn demands better acoustic treatment of vehicles and more emphasis on noise, vibration, and harshness (NVH) performance. More effective noise treatment, therefore, requires more accurate diagnosis and testing. New data acquisition technologies and test methodologies are making it easier, and more effective to identify noise sources.
The traditional approach to noise engineering
All engineering noise problems are system issues and therefore should be treated as such. In practice, however, most noise problems are treated as individual component issues. As a result, tremendous time, effort, and resources can be spent on one target component without showing much improvement on overall system noise performance. The main reason for not treating a noise problem as a system issue is not because of a lack of knowledge but because of lack of the right data collection and analysis tools that enable design engineers to perform a noise diagnosis of a whole system to identify the root sources.
Because of the cost and complexity of traditional instrumentation, traditional NVH approaches rely on acoustic pressure measurement at only a few points and then use complex signal processing to gain insight into the problem Alternatively, intensity scans have been used to map noise sources, but it is usually time consuming and measurement-position dependent. Moreover, results are valid at the measurement points only and sources can be missed or misdiagnosed.
New data acquisition technologies
Historically, NVH engineers often have used data recorders to capture in-vehicle data. Data recorders provided a portable solution for noise and vibration applications with their small size and DC power. However, their functionality is limited, and, among other drawbacks, data recorders are unable to display results immediately requiring play-back and post-processing of data.
Modern data acquisition systems have introduced a variety of new technologies overcoming these limitations and yet have maintained the compact form factor and features for portability.
The first of these key technologies is Hi-Speed USB. A USB 2.0-based data acquisition system provides a maximum data throughput of 60 MB/s, enabling on-the-fly data transfer to PCs and laptops for processing. With this bandwidth, NVH engineers can easily stream 24-bit data at 50 kS/s per channel over 32 channels (6.4 MB/s), 64 channels (12.8 MB/s), or more.
Other significant technologies come from advances in semiconductors. The figure below shows the density of components and circuitry on a modern data acquisition module measuring only about 3 x 3 x 1 inches and weighing about 6 oz.
The analog-to-digital converters (ADCs) have decreased in cost by 85% over the past 10 years enabling affordable, modular, multi-ADC architectures while at the same time increasing in resolution, dynamic range, and speeds. Additional improvements come from new microelectromechanical system (MEMS) technology that provides signal isolation and system protection. Finally, the decreasing size of integrated circuit technology allows for more functionality such as IEPE constant current power for microphones and transducer electronic data sheet (TEDS) smart sensor readers to be included on these portable systems.
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