wavechart for large dataset

[Jordan12]

Dear Labview users,

I am new to Labview, I have tried 2-3 days to find a answer to my problem but couldnt find. I am sorry if someone has already posted this quesion before but I couldnt find.

Actually I am using HP picoammeter to read current values for my circuit as a function of time. In the instrument driver vi, the reading of current is in dbl (double integer). I can connect it to wavechart to see the variation of current with time. But in my case, the experiments will run over long time (6-8 hours) and I read somewhere that in wavechart the data will keep overlapping once it reaches the maximum value. This value by default is 1024 I guess. So my questions are:

1. What is the maximum value of points I can enter to record data before it starts overlapping/freezing due to memory issues in wavechart.

2. I saw in this video (http://www.youtube.com/watch?v=HtjgeoJc4zA) that I can also use waveform graph. I can do this using while loop but in the video its said that its better to intialize an array to avoid memory issues. I dont know how to do this; can someone please post a block diagram for this ?

Thanks

Jordan

[Ben]

The machine you are using presents the real limitaitons of the WF chart. YOu can right-click and chang eht history to something large for a larger buffer. The memory in the machine and the CPU's ability to update the chart fast enough will be your limiations. Experiment with the chart history lenght first to see if we have to complicate this any further.

Ben

[Ryan_S]

Hey Jordan,

      When it comes to changing the chart history, you can manually set the chart history buffer by right clicking on the Waveform Chart and selecting "Chart History Length". From here, you can change the number of data points the chart history stores. The default for waveform charts is 1,024. For a 64-bit double, you can allocate an array up to half of the addressable memory on the computer. For example, if the computer has 4 GB of memory, you can allocate an array with up to 268,435,456 data points. The better method, as you've mentioned, would be to initialize an array, insert the values into the array, then display the array on a graph. I've attached a simple example for doing this in a For loop. You can do the same process in a While loop. 

--Ryan S.

[Jordan12]

thanks for your replies. 

Can you please repost the vi in labview v 10 ?

Thanks

[Ryan_S]

Hey Jordan,

        Here's the VI for LabVIEW 2010. However, I agree with Ben. You should experiment with the chart length and if it satisfies your requirements then there's no need to complicate your VI. Hope this helps!

--Ryan S.