acceleration

[m3m3ngo]

Hello,

  I am inputing an earthqauke data that is in time domain and used the DAQ Assistant to record the acceleration, but my acceleration graph does not match the actual one. Is there a conversion that I need to do? I got this earthquake data from the USGS website and I have a mini shake table. I am trying to replicate this earthquake and verify tha the acceleraion matches. Thank you for your help.

[ongeelim]

Hi m3m3ngo,

Please provide us your LabVIEW files, so that we can get an overview of the problem.

And what is/are the NI hardware that you use to perform such measurement?

Ee Lim

[Henrik_Volkers]

Shure you where using the rigth scale?

displacement, velocity or acceleration?

How do you source the shaker ?

FRF of the shaker?

[m3m3ngo]

Hello, 

    The attached file is the code and setting for the accelerometer. I am using the cDAQ-9178 to measure the shake table. I believe the data I am feeding into the shake table is a distance vs. time and the accelerometer is measuring in g. However, when I did the conversion by multiplying the recorded data to 9.81 m/s^2, my result is still not right. 

[m3m3ngo]

The attached file is a sample of the data I recorded and plotted.  If you compare it to the front panel plot, it does not look the same. Thank you for your help!

[Henrik_Volkers]

Well , acceleration is x (d/dt)² mean: to get the acceleration you have to differentiate the signal twice

here

http://forums.ni.com/t5/LabVIEW/Derivative-problem/m-p/2545553#M770893

i posted a vi I use to do that.

Now: What does your shaker need as input?

[m3m3ngo]

The earthquake data we put in, is distance and time, so wouldn't that mean the graph should come out the same? When we use the acceleration in the DAQ assistant, isn' t it measured in g? Overall, I have a distance and time record and with the data I exported from the DAQ assistant is in g, so does that mean I need to integrate twice to get my data into distance and time? Wouldn't the FFT do that for me? Thank you.

[m3m3ngo]

I am using 5 volts to send the signal to an acutuator to create motion. My labview program seems to work well with reading in text file of time and distance data and running the shake table, but my challenge is to validate that the acceleration I measured from the accelerometer matches the input earthquake data. I took an earthquake data from USGS and converted it into distance and time then scaled it down to fit the mini shake table because the motor running the shake table has a travel distance of 2.8 inches to the left and 2.8 inches to the right. Thus, the full scaled earthquake will not be able to work.

[Balanceman]

Well, the signal you get from the accelerometer is acceleration, as the name says.

If you want to compare it to the earthquake signal, I would integrate the acceleration time waveform twice (Acceleration -> velocity -> displacement.

Further you need to make sure what kind of signal you shaker would like to get. If it is an electrodynamic shaker (coil and magnet) it possibly is moving proportional to velocity. I am not sure about this. But electrodynamic vibration pickups, which are popular for use in seismic measurements, have an output signal proportional to velocity.

Cheers

Gerd

[m3m3ngo]

I tried to integrate twice and plotted the data, but it does no look anywhere close to what I expect to see.What should I try doing different?