How to pause a waveform chart?

[Jaegen]

Hello,

I would like to be able to (simply) pause a waveform chart, while still sending data to it (i.e. I don't want to just pause the VI altogether, I'd just like the chart indicator to stop updating, without losing any data).  I'd also like to be able to scroll the x-axis scroll bar and manually edit the axis scales while doing this.  I've tried using a property node to hold the x-axis range, but this causes flickering, as new data causes the x-axis to change briefly before the property node sets it back.  I've also tried using the front panel "Defer Panel Updates" property.  This works well, except for one bug/feature in LabVIEW: If I set "Defer Panel Updates" to TRUE, the display pauses as I would like, but if I then drag the x-axis scroll bar on the chart, the plot area actually gets properly redrawn - which is actually exactly what I want (apparently the event handler for the scroll bar is ignoring the "Defer Panel Updates" property).  The problem is that only the plot area gets redrawn - the actual x-axis values don't change (i.e. the chart plots display data that does not correspond to the x-axis scale displayed - the gridlines don't even line up with the axis values and tick marks).

I know I could maintain my own data buffer, and stop sending data to the chart when I want to pause, but I'd like to avoid doing this, since the chart is already a nice buffer, and this would use up memory.

Any suggestions?

TIA,

Jaegen

[devchander]

Hi Jaegen,

Have a look at this VI.

I pause the chart by simply placing it inside a case structure.once paused, you can rescale axis, select a portion of chart and zoom it etc.

Hope this helps

Regards

Dev

[Jaegen]

Thanks for this, but unfortunately it doesn't quite do what I need.  I don't want to lose any data while the chart is paused, and this VI does (random numbers generated while the chart is paused are lost).

Jaegen

[devchander]

Well,

If that's your requirement, go for a graph with a shift register as shown

Note: watch out for virtual memory overload while using shift registers

Regards

Dev

[DavidJCrawford]

I hope you don't mind me chipping in here. I have an alternative method that uses two charts and property nodes. One chart is used to store all the data and the other to show the data after a pause. You don't need the shift register here just use the history data collected on the chart.

Have a look and see what you think.

David

[devchander]

Hi Jaegen and David,

David's solution also shows an innovative way of "pausing" the chart.

But Jaegen, do keep in mind that  charts have a limit on the history length or the number of values you can store.

Regards

Dev