Temperature against time

[ehalpin13]

Hi, I'm working on measuring temperature against time in labview (of a thermistor). The data comes in as voltage and gets converted to temperature in the subvi. I'm not sure whether I should be using a waveform or XY graph for this. I've attached the block diagram and subvi.

Thanks!

[GerdW]

Hi ehalpin,

I'm not sure whether I should be using a waveform or XY graph for this.

You should be sure about your requirements!

So what exactly do you want to display?

Waveform graphs are perfect for evenly-sampled data (fixed dt), while XY graphs are nice for data with random X coordinates. (You might also use waveform graphs for non-evenly spaced data when using the waveform datatype…)

Why do you need 2 local variables just to display data in the waveform graph?

[ehalpin13]

Hi, thanks for the reply. I need to log a change in temperature over time so the waveform seems like the best option then! 

Local variables were left over from something else I had tried out. Would it be better to just remove those?

[crossrulz · Accepted solution]

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@ehalpin13 wrote:

Local variables were left over from something else I had tried out. Would it be better to just remove those?

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YES!

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@ehalpin13 wrote:

Hi, thanks for the reply. I need to log a change in temperature over time so the waveform seems like the best option then!

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You might want to consider moving the DAQ reading/logging into a parallel loop so it is constantly running and gathering data.  You could change your graph into a chart then and make things simpler.  You should also make sure your DAQ is set to be continuously running at a set rate (DAQmx Timing VI).

[pallen]

If you're looking to add a data points to "waveform" over time, it sounds like job for a Chart.  

There's an article here on the difference between Graphs and Charts in LabVIEW. 

[RTSLVU]

I use X-Y charts 99% of the time even though they are a bit more cumbersome, I like having complete control over how the data is presented.