How can I obtain a real-time plot in LabView?

[Matt K]

I am trying to plot a force vs. travel plot in real-time format. I have a full development licence on LabView 8.2.1. Is real-time possible with this software or will I need to purchase something else?

[JK1]

Hai,

What are you trying to state by the word 'Real-Time'.  Do you mean the acquisition you are trying to make must be 'real time' or something else....information is insufficiant to help.  Add some more information to the post.

If you are using real time targets like PXI RT, cRIO then you need to install appropriate drivers.

Plot between any two quantities can be plotted using the XY Graph.

With best regards,

JK

Message Edited by JK1 on 06-21-2007 06:39 AM

[mikeporter]

The limit is the operating system that you are running. If the stroke you're measuring is very short, no Windows-based application will work because Windows can not do deterministic realtime operation. What it gets down to is how much variation in measurement interval you can tolerate.

The good news is that there is a version of LV that runs under a realtime OS if you need it.

Tell us a bit more about the measurement you are wanting to perform.

Mike...

[Matt K]

By 'Real-Time' I mean that I wish to view the data on the screen as it is streaming in. I want to see the force vs. travel plot constantly being plotted, keeping the the data from all the cycles on the graph. The plot will look like it is tracing itself.

[Matt K]

Mike,

The measurements that will acquired are for a large MTS compression machine in our testing lab. We use it for the testing of large hydraulic units. The max travel that would be measured would be around 5-7 inches and the normal travel for tests are around 1-2 inches. The iterations of each cycle are about 2-5 seconds. The forces are around 15-30 klbs. Right now we are using a data acquistion software from MTS but we would like to upgrade to LabView since the system is very old.

-Matt K

[mikeporter]

If the data acquisition will be through DAQ cards, this is very do-able from within the Windows version of LV. If you are talking to some sort of external device through a serial interface or something, that could be a problem due to communications lag time.

Mike...

[Matt K]

We will be using a PCI DAQ Card for our data acquisition. Are there any tutorials that you know of regarding how to use the regular developmental verson of LabView for Real-Time data acquistion?

[mikeporter]

Not really, just that standard DAQ examples. The idea will be to setup the DAQ such that the acquisition buffer is big enough that you can treat it as a circular buffer. The acquisition hardware puts data into it at a fixed rate determined by the acquisition clock you define, and LV reads out blocks of data fast enough that the acquisition doesn't over run old data before LV can read it. Check out the example involving streaming to disk...

Mike...

[Brian_K.]

Hi Matt,

Everything Mike has said is correct.  I just kind of wanted to hammer home what is exactly meant by "real-time".  Real-time does not mean fast, but rather deterministic.  In other words, real-time actually means on time.  To accomplish this most real-time applications have to be run on a real-time operating system.  Windows is not a real-time operating system. 

Most confusion comes in because real-time programs are typically faster by nature.  It sounds as if you do not need LV real-time, but what Mike has suggested.  Just a quick clarification.

[Michael_B_other]

Just visit http://www.oscilloscope-lib.com
Salute