Problem with Splitting my Four Channels and Amplitude Control

[Thomas-B]

Hi Tebefia,

I am not sure I understand what it is you are wanting to change. When I run the VI with the Autoscale X and Y on, I can see all of the data well without any trouble. It also continues to show me the entirety of the data up to 25001 points, per the Chart History Length buffer size selection made by right clicking on the graph and selecting Chart History Length. 

If the 4 signals you are reading are small enough that they are insignificant with respect to a 0 to 350 range, it will surely be hard to see, when your scale is set at such a large range. However, autoscale will take care of that for you effectively. Is there something I am misunderstanding?

[Tebefia]

Thomas-B

Thanks for your response.  Your second setence iin your last response was that when you run the VI with the Autoscale X and Y on, you see all of the data.  I have expressed that even in my own question on here, and I have expressed it clearly that I want to run the VI with Auto Scale on.  I want to run the VI based on the ranges I have given for both X and Y, and if you can't find your plots based on those ranges, what could be the reason?  Could it be the rate and number of samples in the amplication?  Hence I sent the vi and the rate and niumber of samples am using, but you still went to run the VI with Auto scale on.  

Thanks.

[Thomas-B]

Hi Tebefia, 

You cannot see your data without autoscaling initially because the amplitude of your data is insignificant with respect to your scale. If you use the amplifying controls on the right hand side of your graph you will see that if you amplify the signals above zero, they can be seen, even with autoscale turned off. At least, this is the experience I am having. What exactly are you seeing? If this does not align with what you are seeing, can you please post screenshots of your front panel, instead of the entire VI itself. 

[Tebefia]

Hi Thomas:

Greetings.  Am sorry for not replying to your last message before now. It's been one thing or the other. Meanwhile, am still on this issue of waveform, and for some reasons, I seem not to understand certain things.  I have attached a vi that was originally crearted by one of your colleagues and I modified it close to my reall application.  I am more concerned about the waveform chart, and not the waveform graph.  These are my problems about this attached vi and I which I humbly ask for any hint or solution that could put a pay to this nightmare.

1. When I changed my X scale as from 0 - 25000, and Y scale as 0 - 300, labview automatically changes it to Auto Scale.  Why is that?  Of course, I did increase the chart history to 25001, yet It automatically changes it to auto scale before plotting.

2. To me, the rate of update/plot is excessively slow and you could tell if you run the program.  What can I do to speed up the plotting?

3. I wanted a behavior in which my four different channels in the In Place Element Structure are separated, but surprisingly that is not the case as you can tell from the waveform chart, as all my four signals are plotted on top of each other.  What can I do to achieve this behavior?

I would appreciate your answers, or anyone responses to my questions.

Regards.

[Thomas-B]

Hi Tebefia, 

1) Basically, what appears to be happening is that, though you are telling the chart to have a window of 25001 points, you cannot override when that 25001 points start and end. The starting point is directly tied to the t0 value you are passing into the chart through the data being read in through the DAQmx Read VI. In order to bypass this, you would have to programmatically clear the data on the chart, and furthermore write over the t0 value in order to shift the data back to a starting point of 0. The y-data doesn't appear to rescale itself, at least on my version of LabVIEW.

How to Clear a Graph or Chart Programmatically in LabVIEW

2) Regarding updating the data more quickly, there are a couple aspects of this issue to consider. You can increase you acquisition rate of data, through the DAQmx Timing VI's rate and samples to read inputs, as well as the DAQmx Read's samples to read input. Additionally, you may want to change the rate of the entire loop, which is controlled by the timing BI in the top right-hand corner of the loop. A combination of changes with these attributes should allow you to get a faster update rate.

3) As far as splitting up your data on the charts, you would need to follow the directions in the KnowledgeBase article I posted previously or use the methods suggested by the gentleman earlier in this thread. I have reposted the KnowledgeBase here for your convenience. If you are wanting the signal on separate charts altogether, you will need to use the split signals VI in LabVIEW to split the data into its 4 signals so you can wire them into their own waveform charts. 

[Tebefia]

Hi Thomas B:

Thanks a whole lot for your response and kindness in answering my questions.  Your response is very well understood.  

Yes, you are right when you said that the Y data doesn't rescale.

Concerning changing my rate and samples to read with respect to possibly increasing plot update, I think am at the max right now using NI USB 6218.

As for the knowledgeBase link you recommended, I must have read thru it before now, and I probably thought it wasn't the solution to kind of behavior I wanted.  However, am going to take a look again.

Regards.

Tebefia