Waveform chart real time plotting

[asai18]

Hello everyone, 

I am a new LabVIEW user and learning the software by following some books and other online stuffs. My doubt is regarding waveform chart, i made a simple program using random number and plotting it on waveform chart. As plot is being generated over a period of time the values on X-axis keep changing. Is there a way such that i can make a program such that my X-axis is always starting at t = 0 and even if run the program for 2 hours the chart should be showing the values from 0 seconds to 7200 seconds. 

I know that a waveform graph can show this. But i want plotting in real time 

Thank you

[GerdW]

Hi asai,

I know that a waveform graph can show this.

Then why don't you use a graph?

But i want plotting in real time 

How is this related to use a chart or a graph? And how do you define "realtime"? (I'm sure you mean something completely different than most of us…)

Is there a way such that i can make a program such that my X-axis is always starting at t = 0 and even if run the program for 2 hours the chart should be showing the values from 0 seconds to 7200 seconds. 

To answer your question:

- set the x axis to autoscale

- set the chart history to a value allowing the chart to buffer enough samples…

Why this is bad:

- how do you want to display values from 7200s to a chart of ~500 pixels width?

- allowing large history buffers will make your VI slower

[asai18]

Hello sir,

Thank you for the reply. 

Okay let me give more clarity about my problem. Suppose i am measuring temperature and plotting it on a waveform chart, after 3-4 hours of running VI continuously if i want to see what is the temperature at 15th minute on a waveform chart how can i manage to do that? 

Since i am going to work on real time monitoring of bio-process reactions which take place for 36-48 hours. And i want to know what happened to particular parameter at 3rd hour for example how can i visualize that on waveform chart? 

As you have mentioned if i increase buffer VI is becoming slow. 

[GerdW]

Hi asai,

Since i am going to work on real time monitoring of bio-process reactions which take place for 36-48 hours.

48h at sample rate of 1S/s gives you 172800 samples/channel: set your chart history at least this size…

But: the data of one channel will need 1.4MB of memory. How many channels do you use?

As you have mentioned if i increase buffer VI is becoming slow. 

Separate data display from your DAQ loop using a producer-consumer scheme.

Store your data also in a file (this should be done even before displaying the data in a chart).

how can i manage to do that? 

As said before: set x axis to autoscaling and increase chart history size…

General comments:

- Usually you don't display that large amount of data on tiny charts or graphs.

- Usually data is decimated before display (to minimze memory footprint and use a reasonable amount of pixels as mentioned above).

- You could keep your data in memory (1.4MB per channel, with 100 channels still less than 150MB) and only display the relevant data in a graph: let the user choose time range and filter your data as needed…

- keep a log file with relevant notes (like "channel AB has changed significantly at HH:MM")…