graph - time?

[Viller]

hi

I have a small problem with the "waveform graph" - what I want is the X-axis to diplay the time (this is easy:-) ) but I want the time to start at Zero and the display seconds from when I start the VI?? when I choose "relative time" its displaying seconds but not from zero?? - another thing: the data displayed in the graph I also write to a spreadsheet file and I then use the "tick count [ms]" which is also written to the spreadsheet in order to get a "timestamp" for each datapoint!! this works ok! but isent there someway that the graphblock can give the timestamp?? hope you understand what I mean?? 

[daveTW]

Hi Viller,
there is an option called "ignore timestamp" in the graph context menu, this should force it to start at zero.
The second question I don't quite understand: Is the graphblock your waveform graph indicator? And when the data isn't coming at a fixed rate, then you have to use the XY- Graph with the timestamps as X- Values. Then you can use these for the spreadsheet...
Greets, Dave

[Viller]

ok I guess I didnt explain myself very clear! I'm a newbe at Labview, but have ealier worked with simulink and when you place a scope in simulink the x-axis automaticly displays the time in sec from when you start! ------- My question was: isnt there a more simple why to get time stamps to the data I write to the spreadsheet??  

[daveTW]

Hi Viller,
I still didn't get it all, but if you don't have a timestamp for every Y-value, you need to create it for yourself. For an example I made a solution in the simple and the cool way:



Greets, dave

Message Edited by daveTW on 02-27-2007 11:56 AM

[Viller]

ok.... what is your opinion on generating a timestamp on the following way : "see attachment"

[daveTW]

I suppose, this is a scratch. Else I would have the first question: How do you stop the loop? But second question: Why do you use a shift register, since the data is never changing. It's enough to just wire the tick it into the while loop.
If you want to make some measurement in the loop I would recommend the timed loop, it ought to be more accurate. And if it's important to have the "exact" time the measured value comes in, you should bundle the Get Tick Count with the aquiring VI (e.g. the VISA Read) with a single frame sequence.
Where do you get the data from? How do you get it into the PC?
Greets, Dave

[Viller]

hmm I dont know why I have used a shift register because you are perfectly right  there is no need for it! the data is suppose to come from voltage measurement (cDAQ) but this is notimplemented yet! when you say bundle the data I guess that you mean to bundle the "timestamp" and the data before writing it to the spreadsheet!? and i have alerady done this.