Sensing vibrations within a building

Technical Support
1

Hello,

I want to set up several Raspberry Shake devices on an isolated network not connected to the Internet - gather data - and try to determine if I can subtract the data gathered from a device that I have located in the basement from the data I collect on the 2nd floor. Is this possible with the devices and software that is available?

Apologies if this has already been answered in another forum area.

Thanks,
David.

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2

Hello David, and welcome to the community!

No problem at all; feel free to ask any questions you need. It is indeed possible to set up a network (isolated from the outside) to monitor building vibrations.

For this, I would recommend an array of RS4D models (RS4D | Strong Motion Seismograph) which sensors should be the most suited for this kind of research.

The question is to maintain synchronized and correct timing between all Shakes. As you are working with multiple instruments, I would recommend synchronising the various devices’ timing via a single PC server. We have some documentation here on our manual, on the dedicated NTP page: NTP and GPS timing details — Instructions on Setting Up Your Raspberry Shake

The computer that would run the local NTP server can be any computer whatsoever: a regular PC, a laptop, or even another Raspberry Pi.

The basic idea behind this is that you have a local computer that has two things:

  1. a connected GPS device (or a constant internet connection) that governs the hardware clock on this computer
  2. running an NTP server (not the client daemon) to which a Shake Pi will connect to use as its NTP server

In this way, you will have a single NTP server that will regulate the timing of all the connected devices instead of having multiple NTP connections for each device. This will give you an improved level of accuracy, ensuring that all your devices are in synchro with each other, and all their data can be promptly used together without the need to check for the aforementioned synchronization.

If you have any other question(s), I remain available.

3

Hi Davishue

Depending on the building, you may only measure vibrations through the RS4D geophones, the RS4D accelerometers sometimes do not have sensitivity for low intensity vibrations (they are designed for strong motion). The most important thing is that they are synchronized.
To process the data, you can use any software that does frequency analysis (Rsudp, Sward, Obspy, etc.)

If you check the frequencies you have in the basement and those recorded on the 2nd floor, you can identify the modal frequencies of the building.

Alejandro

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