Vibration measurements – the old way
Traditionally vibration measurements for obtaining natural frequencies and damping is performed with a large setup including: Folding table, data acquisition board, amplifier, PC, accelerometer and a lot of wires.
This setup gives the most accurate measurements and is still the preferred method when doing vibration measurements, where high accuracy is required (e.g. laboratories). However, in 80-90 % of the cases in the construction industry the measurements can be acquired with the accelerometer in a smart phone. The benefits of this is fast execution of projects, which leads to a significant reduction in costs. In addition the results can be review quickly on-site to determine if the required data have been achieved.
App for vibration measurements
The app Vibsensor can be utilized to obtain and store the measured vibration data. The app is free on App Store and Google Play. The premium version has a cost of approx. 7$, which enables data export.
In the data below is a visual representation of the spectrum and in the 2nd slide a time series. In the spectrum view, Vibsensor shows the frequency for which the highest peak occur. The frequency is often af natural frequency. In the spectrum below that is “Z: 15 Hz (…)”.
The accuracy of the accelerometors in smart phones have been investigated in several scientific papers with great results, see examples here.
The exported data from Vibsensor can be analysed in e.g. MATLAB or Octave. This enables the option to present the data from the vibration measurement in figures. In addition the data can be utilized to obtain the damping (which is not possible directly in the Vibsensor app). The damping can be estimate by a decay test or a spectral method where the width of the resonance peak is investigated.
For measurements of natural frequencies and damping the structure is normally excited by a heel-impact or jumps as shown in video below.
For more info and examples of vibration measurements go here: