vibration monitoring--some help needed!

[DiPS]

Hey!

i am trying to create a simple VI for vibration monitoring.... just some basic stuff like getting rms, pk 2 pk values etc

however to do so i am reading from a sprdsheet acceleration values in m/s^2(obtained from an accelerometer by another prog..)

to simulate DAQ acquisition i used a FOR loop to read the values one by one and this works fine...

However i have the following problems/questions:

1. is it not possible to integrate the signal in the time domain to get velocity... i tried doing it but got a blank graph

2. is it possible to do FFT specrum analysis on this signal... how to go about this? again, i tried and got a blank graph

i'm doing all this within the FOR loop

3. also i have another spreadsheet file with two coloumns x=time data, y=accl data but i am not able to read values to a xy- graph one by one ie. plot values with a delay to the graph to simulate daq, like i'm able to do with a single coloumn and express graph

4. how to get the current system time on x-axis instead of LV default 5:30 1904

5. finally, in "SIMULATE ARBITARY SIGNAL>>define signal" is it possible only to enter data manually cell by cell, can't i put all cells from a spreadsheet(tab delimited txt) file

thanx

DiPS

Message Edited by DiPS on 04-16-2007 11:49 PM

[Nadim R]

Hi,

1. is it not possible to integrate the signal in the time domain to get velocity... i tried doing it but got a blank graph

Yes, you can integrate a signal in the time domain.  Have a look at the integral.vi example in the Example Finder.  Notice that it is a waveform that requires not only signal data but also time data.

2. is it possible to do FFT specrum analysis on this signal... how to go about this? again, i tried and got a blank graph

Have a look at this tutorial when using FFT in LabVIEW. 

3. also i have another spreadsheet file with two coloumns x=time data, y=accl data but i am not able to read values to a xy- graph one by one ie. plot values with a delay to the graph to simulate daq, like i'm able to do with a single coloumn and express graph

To express data one by one (one time per acc), you would need to use a double for loop and extract element by element out of the spreadsheet.  Then you will be able to plot on the graph.

4. how to get the current system time on x-axis instead of LV default 5:30 1904
The difference is between Absolute Time and Relative Time.  I have copied the contents of the help in regards to this question here:

• Absolute time—Displays the numeric object in terms of time elapsed since 12:00 a.m., January 1, 1904, Universal time. You only can set absolute time with the time stamp control.
• Relative time—Displays the numeric object in terms of hours, minutes, and seconds starting from zero. For example, 100 in floating-point notation equals 1:40 in relative time

5. finally, in "SIMULATE ARBITARY SIGNAL>>define signal" is it possible only to enter data manually cell by cell, can't i put all cells from a spreadsheet(tab delimited txt) file.
You will have to convert your tab delimited text file into an LVM file, if not already done so.  You will then be able to load your file into the Simulate Arbitary Signal Express VI. 


I hope this helps!

Regards,

Nadim
Applications Engineering
National Instruments

[DiPS]

thanx for replying

1.OK...but i am reading data(single column) from a spreadsheet.can i include dT into signal.HOW?

5. how to make a tab delimited txt file to an LVM which can be loaded in ARBITARY SIGNAL VI. i tried wiring the output of readspreadsheet>>all rows to signals node of write to LVM but on loading it in ARBITARY SIGNAL>>define signal got just one cell

Thanx Again

DiPS

[DFGray]

1. A single column of data from a spreadsheet does not include time data (dT).  You have to get this value from something else, perhaps another column in the spreadsheet.  The common methods for doing this are to store the dT explicitly in the file (LVM does this) or store the time values as another column in the file (typically done with samples taken at random intervals, but sometimes used with evenly sampled data, when storage size does not matter).

5.  If you have a tab-delimited file, you do not need to convert it to an LVM file to read it.  You can read it as it is using either Read From Spreadsheet File.vi or Read From Measurement File with Read generic text files option checked.  This assumes all your values are numbers.  Depending upon which you choose, you may need to convert the data from a two dimensional array to a single waveform or dynamic data type.  You can convert from a 2D array of numbers to a waveform by extracting the column you want using Index Array from the array palette, followed by Build Waveform from the waveform palette.  Make sure you fill in the dT value in the Build Waveform.

If this doesn't help, post some screenshots or code so we have more information on what you are trying to do.

[DiPS]

i'll try it...thanx for the reply..

[nerminush]

Hy!

i'm a begginer in this (LabView)

i have a work to do: "Identify operating system damage by monitoring vibrations"

I would be grateful if you could help me with a program or any information, please.

Thanks!

[H_SH]

Hey nerminush,

please start new thread as the above thread is older one with someone specific problem not of "vibration topic" generalised .. Plus write ur requirement not only topic to get some reply

Hope to help u in geting better response here..

HS