plot points on graph

[bhattnbikes]

Hi guys,

      I am taking readings of temperature frequently and plot the curve in graph. At a point i would like to plot the temperature readings i get as points on the same plot. When i try to just plot some points on the graph, Labview joins all the points together and the shape of my curve gets distorted. All i want to do is have a continous curve for readings i get over 3-4 hours and plot just the points on the graph at an instance i select to. I am looking for some suggestions.

[becktho]

Hi

Did I understand you correctly? You display a temerature curve and sometimes you want to display just some special point? How do you select these points?

[Ben]

"When i try to just plot some points on the graph, Labview joins all the points together and the shape of my curve gets distorted."

The value "NaN" can not be plotted so any time a NaN value occurs in a plot, a break will occur in the line connecting the points.

So just insert a "NaN" any time you want to "Lift the pen".

Ben

[guddu]

Thank you guys for replies.

I think i was not clear in asking my question. I need to plot a curve taking temperature measurements over 3-4 hours of period. During that test, one of my elements turn on/off so at that time i have to take the temperature reading and plot the readings as point so that later when i see my graph i can observe at what time after starting the test and at what temperature exaclty did my element turned on/off.  I tried to add "NaN' ,but Ben i need a continuous curve as well as those points on the graph. I think i am now clear in asking the question. Waiting for suggestions.

I am attaching a file in paint showing something i would like to see on the graph. The point  with X marked on the graph would be the points which i would like to plot.

[becktho]

Just an idea: you could use different plot styles.

[PJS]

I have attached a quick example that shows (only) two (of many) ways to do this.  Using cursors and using a secondary plot.  Each has advantages and disadvantages.  Since I am not sure what you are doing with the output data, not sure what would be most convienent, but they work.

[guddu]

Thanks Pana-man for your response. Your Vi does some stuff similar to what i want. But the problem i face is that my test run over 3 hours and i take a set of data when some of my components cycle and i need to plot only those values in the graph once but continue to keep plotting the graph throught the 4 hours of test. I am new to labview so i dont have many ideas how to do it.

[Megan B.]

Hi Guddu,

I'm still a bit unclear on what you are trying to do.  Pana-man's VI seemed to work just like the image you posted.  It sounds to me like you will be continually logging temperature for several hours, and at certain points also want to add some extra plots on to your graph.  If this is the case, you can use multiple plots and use NaN values during the points when you don't want your secondary plots to show up on the graph.

If you're new to LabVIEW, you may want to check out our Three Hour and Six Hour LabVIEW Introduction Courses.  Great resources when you're still getting familiar with the environment.

Good luck!
Megan B.
National Instruments