Vibration analysis vs Low Frequency Detector

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.

"Low Frequency Detector" is an acoustic measurement tool for detecting low-frequency sounds that is hard to hear in normal situation. The human ear is not sensitive enough to low-frequency sounds. If you are exposed to noise from nearby construction or factories without realizing it, you may feel discomfort or a sense of pressure. In such cases, you can use this app to check what kind of low-frequency noise is present. Generally, low-frequency sounds is a sound wave ranging from 1Hz to 100Hz. Depending on its frequency component and sound level, the degree of influence on the human body and the noise sensation is different. This app allows you to examine the frequency component of low-frequency sounds by 1/3 octave band analysis and FFT analysis. Features: - Low-frequency power level measurement less than 100Hz (LF Level): Flat characteristic, Updating indication of measurement period 1 sec. - Power level measurement in the audible band (Leq): Flat characteristic, Updating indication of measurement period 200ms. - 1/3 octave band analysis (OCT) - FFT analysis (FFT) - Time course graph (TIME) - Snapshot (Snap) on the measurement display screen. - Report function (Report): Analysis report of a peak LF Level with TIME, OCT and FFT. - Measurement time: up to 60 sec Functions: The measurement analysis is performed in the following step. Be sure to set the measurement conditions in Step-1 once before starting the sound measurement. 1) Calibration (Calibrate): The reference signal (1kHz sine wave) is output to determine the reference noise level for the low-frequency component. If the volume level of iPhone is set to about 20-50%, the calibration will automatically adjust it to the optimum volume level for the reference signal. 2) Measurement (Measure): Analyze a power level of low-frequency sounds. - LF Level (dB): Low-frequency power level less than 100Hz. - Leq (dB): Sound power level with the frequency weight characteristic Z (Flat) of the audible band. 3) Measurement display: It can select either 1/3 octave band frequency analysis, FFT analysis or Time course graph. They are updated in real time. 4) Report: Measurement result report. It is effective when measuring for 10 seconds or more. # Time course graph: TIME - Low-frequency (LF) Level (dB): Time course graph with peak level noise level judgment (RED-very noisy, YELLOW-noisy, GREEN-normal) at the peak level. - LF max (dB): maximum dB value of low frequency. # Frequency response graph: OCT, FFT - OCT Band LF max (dB): maximum dB value in 1/3 octave band at LF max observation. - Max Level Frequency (Hz): peak frequency at LF max observation. Notes: - The sound measurement of the low-frequency range is a level difference with respect to the reference signal, which indicates the relative power level. - The reference signal is output during calibration and sound level measurement. - Do not change the volume level of iPhone after the calibration. - White line in the OCT and FFT modes indicates frequency characteristics in frequency weight correction of G characteristics. - Since iPhone's built-in microphone has a lower sensitivity on the very low frequency range, it is not recommended to measure a huge volume sound near a very loud noise source. - Since it takes a while for the observation value to stabilize immediately after the start of measurement, the maximum value is calculated from about 2 seconds later. - In the case high power of 1kHz component is included in the measured noise source, the precision of measured value by this app largely decreases. - Sudden noise or impulsive sounds are not low frequency noises in general. - The previous calibration information can be maintained internally. - The analysis results may vary due to individual differences in iPhone devices. - The authorization to access built-in microphone and Photos will be confirmed by iOS system at first access. Please visit our iOS app support page for more information.