Hi all, is there any way to measure vibration of apartment floor, the vibration may caused by a motor installed under the floor.
I have tried several vibration meter apk for android mobile phone, but their results can not directly reflect the vibration's frequency or record it as an evidence.
I'd be appreciated if anyone could recommend any better ways for such measurement.

 

Hello,

Have a look at this page:
https://blog.mide.com/6-ways-to-measure-vibrations

Bertus

 

I would start with the link Bertus posted above. You may also want to read Practical understanding of key accelerometer specifications by Endevco. You will find in your reading there are several ways to go about it and depending on what results you wish several cost factors. You start with a sensor and then determine how you plan to mount the sensor, the sensor's output type, how to amplify the sensor and the sensor's frequency response.

Below is a crude example of me taking vibration measurements off a common house fan using a magnetic base sensor and recording the data.


The resulting random vibration signal.


So it really depends on how far and at what cost you want the project to take.

Ron

 

The first thing I would try is either placing a heavy weight on the phone or finding a way of fastening the phone rigidly to the floor, I guess the other issue is that there are likely to be other vibrations, from passing traffic, people, etc. which may add noise to the signal you are trying to measure.

 

Hi guys, thank you all very much for giving me very helpful suggestion!

The floor is at the top, namely, the 14th floor of the whole building.

I feel horizontal push force and up-down hit while sleeping on the floor (sometimes the up-down hit is so strong that my heart and body feels like suffering electric shock), and also up-down pulse-like vibration while touching the mouse of my PC on a desk standing on the floor, and left-right shake-form vibration while sitting on my chair.

My aim is to collect evidence that the floor vibrates (not because of passing traffic, people, etc.) due to some kind of machine or tool installed under the floor or on a wall downstairs. The apartment owner advised me to take videos as evidence, but I wonder if vibration could be recorded as a video. So, I think acquiring vibration data maybe simpler, and now, I know a sensor is indispensable for this solution. Except that, is there any other way to prove vibration of floor? I look forward to your skilled methods, thank you very much!

 

You might consider one of Adafruit's accelerometer breakout boards, such as this one, which measures down to ±2g full scale on three axes. If this vibration is strong enough for you to actually feel, their sensor should be more than adequate to register it. Adafruit also has a tutorial, complete with code, on how to interface it to an Arduino.

 

So, I think acquiring vibration data maybe simpler, and now, I know a sensor is indispensable for this solution. Except that, is there any other way to prove vibration of floor? I look forward to your skilled methods, thank you very much!

First you need an accelerometer within your budgetary constraints. Vibe measurement can be very complex and expensive or very inexpensive. Depending on how exact you want measurements. I have used the sensors (or similar) mentioned above along with as mentioned an inexpensive Arduino micro-controller. I used them to measure tilt of an axis, this is not what I pictured above. Something I have not done with that type setup is record the data. You would need to make allowances for that and if you ever plan to present the data you will also need to date and time stamp the data. The image I showed above is just a snapshot of a recording of the data. So in addition to reading and displaying the data you need to have the ability of recording the data over a given period of time. This way when the data is viewed it will go from a stable baseline to some level of vibration (change which is discernible).

I have no clue what your location is but is anyone else in the building experiencing this movement phenomena? Does it only happen during certain hours? How close are you to, for example, an elevator machinery room?

Ron

 

If the vibration is that obvious, you should be able to get a small object to dance around and video that as evidence.

Bob

 

Try a cup of water on the floor, lit from the side. Vibrations will show as rings in the water in the cup.

 

Hi OBW0549 and Ron, thank you so much for the detailed information.

I suspect that a motor is deliberately installed under the floor of the apartment that I live in. The vibration of floor occurs since two or three days after I moved in one month ago and lasts till now, I'm basically very quiet and did not make any noise (no TV sound or music or cooking noise), but I guess the neighbor downstairs might just want me to move by using such tool. The motor, according to Internet search result, can vibrate and beat a wall or floor which it is tightly in contact with and cause resonance, and can be remotely controlled through a WIFI plug and has auxiliary settings such as timing and playing sound, etc.

As the motor can cause vibration and beat almost "randomly" (such as a few times per minute, or a few seconds or minutes every time), it is very hard to prove by only making vibration data acquisition (like Ron said, to prove it, one must have the ability of recording the data over a given period of time). So I will try to do as you suggested and at the same time think about some method which is visual and can be recorded as a video. If you have any ideas, please kindly let me know, thanks a lot!

Hi Bob and djsfantasi, thank you a lot for your good ideas!! I will try these methods immediately!

 

It is possible that a human activity enters in vertical resonance with the structure. A "well known" case is given, for a 39 story building at https://www.sciencedirect.com/science/article/pii/S0141029613004471

You should be able to measure the frequency with a laser beam light fixed on the wall (the wall is assumed to be "fix") with the laser beam ray as parallel as possible to the floor, but hitting it at it middle long span (if you prefer, have the laser beam as low as possible but intercepting the middle of the floor). The intersection of almost two parallel lines (the floor and the laser ray) is highly dependent of the exact slope of either line. So, under a floor in vibration, you should be able to see the laser spot on the floor moving back and forth the center of the floor. You should so be able to get the frequency with a light detector (the laser hitting and leaving to hit again, moment later, the light detector), or counting the frames from a movie you would have recorded, having the frame rate of the camera.

 

... something related to lasers, as mentioned by vanderghast, above, ought to work. Try getting a washbasin or large pan of water, and finding some way to float a mirror on top of the water. The idea is to have a reference frame for the mirror that is different from the reference frame of the vibrating building. Hopefully, the mirror floating on top of the water will be isolated and not move in unison with the building. ... a fact in some doubt at this point. At any rate, aim a laser pointer at the mirror floating on top of the water in the basin. Then watch the beam reflection on the ceiling. If everything works as planned, the reflected beam on the ceiling should produce video evidence of the relative motion between the mirror and the building.
QED ... maybe.

... one of those air tables, used to play table hockey, would probably be ideal as an independent mirror reference 'mount' ... However, obtaining one of those would be a project by itself.

 

Why are you convinced that someone is out to hurt or harm you?

 

A PZM microphone + recording in Audacity has to work well.

 

Hi everybody! Thank you so much for providing me various smart ideas for the vibration issue that I encountered.

Considering budget, time and spirit consumption, I tried "VibSensor" app to record data when vibration is sensible to me, and the data charts are uploaded as below:
https://www.filedropper.com/1-2febvibrationrecorddatachart

Please advice me if these charts can be evidence for the vibration issue, based on the table below, as the recorded data charts show that vibration in x, y, z three axes are in the range of 0.3-0.8 m/s2.

(source of the table: https://www.avsforum.com/forum/113-...8090-vibsensor-accelerometer-test-thread.html)

 

For example, on the chart "1Feb.06.27.48.jpg", it shows, during time 0.0-100.0, there were two large shocks on z axis (direction vertical to the floor), which were very sensible to me, and at that time I was sleeping on the floor while the phone was laid also on the floor nearby for recording data.

Ps: User guide for the "VibSensor" app is given below for your reference.
http://www.now-instruments.com/get-help/5-vibsensor-user-guide

The meaning of the Chinese words in the charts are as below:
月: month
2月: February
上午: am
下午: pm

These data charts were named by their record time, and by comparing all the data charts with the last chart "2Feb.08.26.00.jpg", differences are obvious.
Besides, the record time of these data charts shows that vibration does occur during deep night till morning.

 

First, to be a proof, you need to validate that the sensor is calibrated right AND that you are using it in the appropriate manner.

Second, giving too much is like giving none. As example, one file gives and horizontal and vertical acceleration in excessive mode, while others give just either horizontal, either vertical, so the whole set may indicate that something is wrong with the manipulation of the sensor. Same for one of the reference, the one that is said to come from engineeringtoolbox.com, seems familiar but a little bit wrong. My reference, from "SJI Technical Digest No. 5, Vibration of steel joist-concrete slab floors" indicates that at 2Hz, an amplitude of 0.01 inch is not perceptible, that is 0.25mm which, accordingly to the supplied chart, is past unpleasant toward very unpleasant. Not the same conclusion at all, as you can see. Even if the dynamic response depends greatly of the source (impact, transient, continuous) and damping, someone, with your data, may show, right now, that there should be no concern, even assuming that you used the sensor right.

The complete SJI document that I mentioned should be available at Steel Joist Institute, 2001 Jefferson Davis Highway, Suite 707, Arlington, Virginia 22202 - tel: (703) 920-1700


NOTE: something, like you bed, MAY amplify the relatively small vibration, due to resonance, so I do not say that you don't feel the vibration, just that directly on the floor, if it is a steel joist under a concrete slab, you should not feel it. But your bed can amplify it, definitively.

 

one file gives and horizontal and vertical acceleration in excessive mode, while others give just either horizontal, either vertical,

Hi vanderghast, thank you very much for your analysis and opinions!

Allow me to explain, for all the charts, vibration data in x,y,z three axes recorded during the same period of time are shown in the same chart, however, in each of these charts, vibration in one or two directions are stronger than that in other direction(s), that is why it seems, as you mentioned, "gives and horizontal and vertical acceleration in excessive mode, while others give just either horizontal, either vertical" .

Same for one of the reference, the one that is said to come from engineeringtoolbox.com, seems familiar but a little bit wrong. My reference, from "SJI Technical Digest No. 5, Vibration of steel joist-concrete slab floors" indicates that at 2Hz, an amplitude of 0.01 inch is not perceptible, that is 0.25mm which, accordingly to the supplied chart, is past unpleasant toward very unpleasant. Not the same conclusion at all, as you can see.

Also thank you for giving your doubt and your reference file.
Please disregard the graph marked with "engineeringtoolbox.com", which is not used as a reference in my previous posts.
Instead, the table below the graph is what I used as a reference, because all the charts that I obtained only provide peak accelerations, but not displacement amplitudes.

NOTE: something, like you bed, MAY amplify the relatively small vibration, due to resonance, so I do not say that you don't feel the vibration, just that directly on the floor, if it is a steel joist under a concrete slab, you should not feel it. But your bed can amplify it, definitively.

Allow me to explain more, all the charts are obtained by my mobile phone laid on a thin plastic film that is directly placed on the wood floor near the position where I sleep, and I sleep on three layers of cotton mattress laid directly on the floor.

 

a diapason that vibrates at the same frequency as the motor would do the trick as a rudimentary way.

 

In order to document the issue you might want to try one of the vibration monitoring apps. Some of them can record data so you could get the frequency and time for the vibrations.