Chart showing real time versus temperature

[doljam]

Hi all,

Although I can now use Labview at a very basic level I am still very much a new comer to the world of Labview.  I am at the stage in my project where I would like to chart the temperature readings I am getting against time.  I am acquiring the readings every 5 minutes and would like the chart to show the last four days worth of readings.

I have looked through the examples and it would see that I should use a Build Waveform  function but I don't quite understand how it works. Also, when I place the Build Waveform function in the block diagram it won't give me the three inputs. The delta T input doesn't show up.

Any help would be appreciated.

[GerdW]

Hi doljam,

when you place the BuildWaveform function you can resize it - as many other functions like IndexArray or UnbundleByName…

use a Build Waveform  function but I don't quite understand how it works

It takes t0, dt and Y values and builds a waveform from them…

[Dennis_Knutson]

First, you don't have to use a waveform. That is often more complicated than it needs to be with single point writes. You can set the offset and multiplier of the chart where the offset is your start time and the multiplier is the dt. These can be set on the block diagram with property node or selecting the chart's properties on the front panel. Also set the axis for absolute time.

If you do decide to use a waveform, drag It down to get the additional inputs.

[ctVolFan]

I would highly recommend using a waveform graph for this task. The waveform chart is difficult to work with and not worth the time to figure it out.. I know because I have wasted a lot of time trying to plot temperature vs. time with the chart. The chart also has some strange unpredicatable behavior when trying to modify it with properties nodes. Trying to modify the X (time) axis is particularly prone to problems. 

Think about putting the data in an array and plotting it on a waveform graph. You will have much more control over the graph and data and minimize time wasted on figuring out how the waveform chart works.

[crossrulz]

What I have done is actually create a waveform (even with just a single point) and write that directly to the chart.  It just uses whatever time in the T0.  That is by far the simplest way to handle this.  The Build Waveform is expandable to show all of the parts of the waveform data type.

[doljam]

Hi,

Many thanks for the replies.  I would still like to try and use the waveform chart but if I get frustrated I will try the suggestion of a waveform graph.

In the data section of the build waveform function, is it possible to wire the input directly from the acquisition data one point at a time.  Or is it necessary to build an array first and then wire that in.

Many thanks for your help so far.

Doljam

[GerdW]

Hi doljam,

a waveform consists of t0, dt and an array samples. Point.

So you will need to provide an array of samples…

[doljam]

Hi Again,

I have my chart now displaying how I want it to excpet for one thing.  There are only two values displayed on the x axis.  These are the two values flanking the history length.  For example in my case I set the sampling rate to 5 seconds and the history length to 10.   The only two values that display on the chart are ones that are 50 seconds apart.  Is there any way that more values can be displayed along the x axis.  Ideally I would like to see values for all 10 points in the history.

If not I may have to use a graph because I would like people to be able to see the last 2 hours of data and roughly correlate a time to any abnormalities in the graph.

Cheers,

James

[Dennis_Knutson]

With only 10 samples for a history, your chart will only display 50 seconds worth of data so it seems its doing exactly what you programmed it to do. Basic arithmetic - 5x10=50. To display 2 hours worth of data, the history length should be made bigger to accommodate that number of samples - 60/5 x 60 x 2.

[doljam]

Hi,

I agree that it is working as specified but I would like all 10 time values to be displayed on the x-axis.  Only the first and the last are.