WBV vs Vibration analysis

Whole-body vibration refers to the vibration transmitted to the human body whilst supported by a vibrating surface. The most common exposure occurs through the buttocks when seated in a vehicle. Long term exposure to high amplitude whole-body vibration is strongly associated with the development of back pain and other adverse health effects. The Whole Body Vibration application (WBV) utilizes the accelerometer within an iPod or iPhone to provide an estimate of vibration amplitude consistent with the methods described in ISO2631.1. Frequency weighted r.m.s and VDV values are presented graphically with reference to the health guidance caution zone for exposures of varying durations. Summary data and acceleration time series are available to be emailed or downloaded. The application is intended for use within occupational contexts to provide a simple screening or monitoring tool for use by workplace safety and health staff. It is suitable for use to estimate whole-body vibration amplitude of seated operators of all vehicles, plant or equipment. Use is straight forward. After entering trial information, sampling is commenced with a tap and the device placed on the operator’s seat during a period of normal operation. At the completion of the period, sampling is ended with a tap and the results calculated and made available for viewing and emailing. The application has been developed by the consultants at the Byte Works under direction of Robin Burgess-Limerick, Professor of Human Factors in the Minerals Industry Safety and Health Centre at The University of Queensland, AUSTRALIA. The project was funded by the NSW Coal Services Health and Safety Trust. WBV supports the use of GPS, optionally in the foreground and always when background processing is used. The location information is included in the raw data file, which is available using the export features. Continued use of GPS running in the background (or foreground) can dramatically decrease battery life. You can turn GPS on or off using the WBV preferences, available from the Settings app.

The application analyzes the data from the phone's accelerometer and builds a vibration spectrum. This allows the evaluation of not only the strength and frequency of the vibration, but also the speed of rotation of various mechanisms: fans, motors, various rotating components; since the vibration frequency often (but not always) coincides with the frequency of rotation. The application will be useful in determining the quality of fans and motors, in determining whether their actual parameters coincide with the ones declared by the manufacturer, it will find its uses in monitoring of malfunctions (e.g. in bearings) or while testing the quality of assembly and balancing of the homemade mechanisms with rotating parts. Do not expose your iPhone to an excessive vibration, as it may break. If the analyzed vibration is too strong, use a foam material pad, or put your iPhone at a distance where the force of the vibration is not dangerous to your device. In addition to decreasing vibration for the iPhone, a foam pad improves contact between the iPhone and the vibrating part, which makes the transmission of vibration more accurate and produces better results. BE SURE TO READ THE EXAMPLES OF THE VIBRATION SPECTRUM ANALYSIS AT THE APPLICATION WEB SITE (usefulmobileapps.com). Features of the full version of the application: • The choice of units of measurement. X-axis: Hz or RPM. Y-axis: g, m/s², ft/s², mm/s, in/s (ips), mm, mil, dB(A), dB(V). • FFT size (for built-in accelerometer): 64, 128, 256, 512, 1024, 2048, 4096 (data collection time from 0.64 sec. to 40 sec.). For an accelerometer connected to the headphone jack FFT size from 2048 to 131072. For Bluetooth-accelerometer FFT size from 512 to 32768. • Linear and logarithmic frequency scale. • Linear frequency scale with maximum details (there is a choice for the displayed frequency range). • Peak frequency detection. • Values of any point (for frequency scale and sound wave (at maximum detail)). • Selecting which axis of the accelerometer is to collect data. • Octave bands (1/1,1/3,1/6,1/12). • Window functions (Blackman, Hamming, Hann (Hanning), Blackman–Nuttall, Gaussian, Flat top). • Peak hold. • Exponential spectrum averaging. • Taking a screenshot by lightly touching the screen. • Root mean square (RMS, for vibration) or average value (AVG, for absolute values) for vibration wave. Values are calculated only for data displayed on the screen. • Calibration of the built-in accelerometer. Need EXCLUSIVELY for measuring absolute acceleration values (gravitational acceleration). To activate the settings, turn on the "Vibration wave" mode and turn off the "Only fluctuations" mode. The parameters of the accelerometer depend on the temperature and voltage of the battery, and may change over time. To obtain stable values, the accelerometer should work for several minutes. • Saving the measurement results in the application. Files with saved data (SavedData_[date]_[time].txt) can be copied to a desktop/laptop computer or transferred to another iPhone using iTunes. • Export data to a text ("Y=[y1 y2... yn]", "y1;y2;... yn", "x1;y1\nx2;y2;...") or WAV file. Number of points is adjusted via "FFT size". To export octaves, use "x1;y1\nx2;y2;...". • Accelerometer connects to the headphone jack (measurement range from 5 Hz to 24000 Hz). • A stroboscope for an external accelerometer (the feature was proposed by Todd French from Los Angeles, California). • Bluetooth accelerometer. When converting acceleration into speed or displacement, at 0-5 Hz frequencies noise starts prevailing over vibration peaks, which is why such frequencies are disregarded when doing the conversion. Should vibration frequency exceed 50 Hz, the peak will be recorded at an incorrect frequency, and hence speed or displacement will not be calculated correctly. Unrealistically high speed or large displacement may be a sign of this kind of false frequency.