Simple Load Cell Monitoring VI

[CE185]

I am trying to create a simple VI to monitor a load cell that undergoes a significant load spike approx 1 time per second.  Ideally I want the program to capture the peak value and display it.  Additionally I would like to display a running average of the captured peak values.  Can someone help out a Labview newbie?  I have attached my best lame attempt so far.  Thanks!

[RavensFan]

Try this.

Message Edited by Ravens Fan on 11-27-2007 08:33 PM

[CE185]

That is exactly what I wanted to do, thank you very much.  I'm pretty new at this and it would have taken me days to figure that out.  The only items I have remaining with this guy is:

1) Add a graphical display to the front panel that shows the scaled signal as a funciton of time.  (Seems like this would be easy but everytime I add the graphical indicator and run the program nothing is displayed)

2) Add a button to the front panel that logs the data to a file (Excel) when activated.

Thanks again for the help!

[Neil.Pate]

you can use a waveform chart. It remembers previous values, see attached.

[Kevin_H]

Hi CE,

Thank you for contacting National Instruments.  If I understand your second question, you are looking for a way to write data to an excel spreadsheet when the user clicks a button.  Writing data to excel can be very easy, and we do offer a couple of example VI's that show how that process can be done.  Click this link to see a discussion forum on writing to excel.

Please let us know if you have any questions relating to this issue!

Regards,

Kevin H

[CE185]

Thanks NRP, that was helpfull. 

[CE185]

Hey Ravens Fan,

Do you know how I might set up a timing sequence that gets feedback from the load cell signal source in order to capture and display the peak for each cycle?  I imagine  it would need to determine the cycle time from full load to to low or no load dynamically and then look for the peak inside of that changing cycle time.

I tried using the peak detector but I could not get it to do what I wanted.

By the way this is a great forum, lots of helpful people 🙂

-CE

[CE185]

Just a little correction to that last post.  The cylce time will not be changing significatly enough to require dynamically calculating the cycle time every time.  It would work fine if it just took a look at the first 5 cycles and then calculated a constant time domain that could then be used by the peak detection code to display the peak value each cycle.

[RavensFan]

I'm not sure what you are trying to do or what you meant by "feedback from the load cell signal source".  I see from the earlier post you are expecting these peaks about 1 per second.  I see you are capture 10 samples in the DAQ assistant at a 50 kHz rate.

Note: one thing that worries me is that 10 samples at 50 kHz takes only 0.2 msec.  I'm not sure if Windows could run the loop that fast to keep up, and that you could lose potential data between iterations of the loop.

Anyway, perhaps you could post an image of what the incoming data would look like and mark it up to show what the points of interest are and what kind of timing information you want to get out of it, that would be helpful.

[CE185]

I have attached a picture of what the data looks like, the scale is not right but this is how it looks.  I went to take some measurements off the machine but it went down right as I was trying to log the data. 

Anyway, let me try to better explain what I am trying to do:

1) Determine the peak of each stoke. 
2) Display the value until a new value is recorded
3) Keep a running average of these peak values and display it.

I have attached the VI.

Let me know if that makes sense.

Thanks,