Derivative help (probably my ignorance)

[Patrick H.]

I am taking the derivative of a position time plot to get the velocity. It is working other than the first and last points shoot up and down excessively. This is probably where my ignorance from not being in a calculus class room in a while is. I assume it has something to do with the way the derivative VI functions.

I attached a sample graph to show what it is doing.

[Patrick H.]

If the data file isnt in there, here it is

EDIT the file extension wont attach so hopefully it is in the Read from VI

[RavensFan]

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@Patrick H. wrote:

If the data file isnt in there, here it is

EDIT the file extension wont attach so hopefully it is in the Read from VI

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??  How can a data file be "in the Read from VI".

What extension are you trying attach?  Post it as .zip file.

[altenbach]

What is the extension of the file you were trying to attach? You can always zip it up.

Your VI does not contain any data. Please do the following:

1. Create an indicator at the 2D array. (right-click wire, create indicator)
2. Run the VI so the indicator contains data.
3. Right click the 2D array terminal and "change to constant"
4. Delete the file IO stuff
5. Saven the VI under a new name an attach it once more.

[Patrick H.]

I run a .lvm file. I kept the IO stuff because it has to read from row 5 down to row 2003 or somewhere around there.

I put the .lvm and .csv in a zip folder.

I didnt know if it attached in the original VI with the VI itself.

But here is the folder and keep in mind, this is a temporary VI to show my graph.

[johnsold · Accepted solution]

You have a very large DC offset in the data.  Average about 5.7 with variations of less than 0.1.  Subtract the mean before you take the derivative.

Top graph is derivative of (signal - mean). Bottom graph is signal.

Lynn

[Patrick H.]

Thank you Lynn

[johnsold]

Patrick H,

Glad to help.  It is often useful to visualize the data which is causing problems.  Temporarily drop waveform graphs on the front panel and look at the data.  When I did that with your data it was obvious that the dc transient was affecting your results.

Lynn