Identification of your mobile capacities

It is a good idea to know tha capabilities of your mobile before making any measure over an existing structure. The identification can be used to compare with your friend phones.

The idea is to know the following parameters of your mobile:

  • How leveled is the aceleration sensor in your phone.
  • How regular is your time serie.
  • What is the sensitivity level of the accelerometer.

All of them have a great influence in the results you can get, therefore it is important to know them.

Proposed test

In order to make this properly, a lebeled location on a non vibrating floor is required. Good candidates are bottom garage slabs without any car movement or seismic event. Heavy basements use to have unrecognizable vibrations for the phone accelerometer.

The steps to follow are:

  • Look for a horizontal plane on the basement you are going to place your phone. If possible, check with a bubble level.

  • Place your phone as flat as possible. Iy you have a silicone sheath try with it. If you have other phone cover that doesn't allow your phone to be flat, remove it.

  • Start a measure and keep it for a couple of minutes. Do not walk or move during this time. Keep as calm as possible.

Analyze the results

Let's see the more important parameters:

  • First, you must check the quality of the time recording. Therefore:

    • Check the frequency sampling. Values about 200Hz are quite common. Values below 50Hz are very poor
    • Check the minimum, medium and maximum time difference between two consecutive records. This time is given in miliseconds. The mean values is equals to the inverse of the frequency sampling. The maximum an minimum must not differ very much. A value of the maximum bigger than twice of the medium value means a poor quality sampling.

  • Convert the serie to a constant time interval serie and hava a look at:

    • FFT figure must be without any peak. This means that there is no frequency preponderance and you have measured mostly noise. That is, the accelerometer is not capable to get the vibration of that rigid floor. If it does, and the test was run following the previous recommendations, can be either, that the floor is not rigid enough, or the accelerometer has a very high quality.
    • The Root Mean Square aceleration can be used as a noise level of your device. Extra information can be obtained with the peak acceleration and the crest factor.