save waveform from TDS3000

[nizam2]

Hello & Good day

I think this post have been asked before. and solved by Dennis_Knutson

(http://forums.ni.com/t5/LabVIEW/save-waveform-of-tds3000-with-time-axis/m-p/2318464#M728026) 

I did the same thing to save my waveform. But when i compared it from the graph( i rightclick at the waveform and export to excell) the data is not the same. 

Here i attached 2 excel file 

1=from push button save (when pressed it save the data)

2= i rightclick at the waveform and export to excell

[Hooovahh]

To be fair neither are good representations of the data.  I assume your channels are stored in memory as doubles, which is 8 bytes of data for each point, for each channel.  Here is an explaination of the range of a double.  My point is you are going to lose precision, unless you have a crazy large number of digits of precision.  

So what I'm guessing is happening here is the rounding is taking place in both cases, and they aren't behaving the same.  I'd suggest posting a VI that you use to save the data, along with some example data.  Then we can see what the actual values are in memory (the 8 bytes per point) and then see how they compare to the logged data.

[nizam2]

Thanks for reply Hooovahh

here i attached my vi. Hope you can help me 😄

[Hooovahh]

Okay I can't run it for several reasons, but I can see that new data can continually come in.  So I'm guessing you are saving your data at one time using you logging routine, then the graph gets updated, then some time later you right click the graph and log that data.  The graph has been updated since then.  You aren't saving the same data, and I don't think you could be able to.  Only if Stop and Save File were true entering the run case at the same time, then the data could be logged and graph updated, but the graph wouldn't update any more.  You could then right click and save it.

Also I'm not sure you are calculating the time column properly.  I'm missing the VIs but it looks like it is always the same value.

As for rounding, you can see you are loggint 3 digits of precision in your routine, but it is unclear how many the right click will preserve.  This is likely why your second channel is always 0 in the right click, and 0 or .002 on the logging routine.

[nizam2]

thanks for replying.

That means the connection is correct? if wrong do you have any idea on how to save the data?

[Hooovahh]

It looks like it might be the right idea.  Take T0 and add DT to it in a for loop for the number of samples in Y.  So sample 0 is at T0, sample 1 is T0+DT, sample 2 is T0+DT+DT.

[nizam2]

Sorry i cant get you this time. If can. Can you explain in term of vi or figure.

[Dennis_Knutson]

I'm posting from my phone so I can't look at your VI, Can you post an image of the block diagram?

My code that you referenced is getting the t0 and dt from the read waveform function and creating an array of time values. What don't you understand about it? The t0 is the start time and dt is the time between samples.

[Hooovahh]

Attached is a quick VI that makes a sine wave.  It will then generate a 1D array of times, to go along with the 1D array of Y values.  These two columns can be logged and you basically have XY pairs of data which I believe you want in your log.

[nizam2]

Thanks for reply Dennis_Knutson

Sorry for the late reply. here i attached is the screenshot in jpeg format