How to modify WaveformChart history data length programmatically in LabVIEW?

[jbao@via-telecom.com]

How can I change waveformchart history data length in Labview during a VI's running?

[Ben]

I have wanted to do this a couple of times myself.

This can only be changed at edit time,
and
it must be done via the pop-up.

What problem does this cause? There may be a work-around.

Ben


Ben Rayner
Certified LabVIEW Developer
www.DSAutomation.com

[Greg_McKaskle2]

> How can I change waveformchart history data length in Labview during a
> VI's running?

Since this buffer is pretty integrated into the execution of the
compiled VI, it isn't possible to change it at runtime. It will
automatically expand to allow new plots in the 2D array case, but the
circular dimension is fixed at compile time.

If you are using the waveform datatype, the buffer is measured in
waveforms, which can each hold any number of points from zero to 2B. So
this datatype does give you another degree of flexibility.

Greg McKaskle

[Ben]

"any number of points from zero to 2B"

Is that 2b hex or "to be determined" or a typo?

I never noticed an upper limit. Is there one?


Ben

[Greg_McKaskle2]

> "any number of points from zero to 2B"
>
> Is that 2b hex or "to be determined" or a typo?
>

2B is my shorthand for ~2 Billion, or 2^31 - 1.

This is effectively the upper limit on LV arrays
since they use a signed I32 to store their size
for each dimension. And of course we are already
having to look forward to the day that we bump this
to a 64 bit number. Joy, joy.

Greg McKaskle

[jbao@via-telecom.com]

Thank all of you very much. I think this is a great place and I can always get useful information here.

[Ben]

No wonder I never noticed the upper limit!

Ben

[Ben]

One more thing jbao,

THe best way to thank someone on this exchange is to give the best answer a four star rating.

This way others in the future can quickly find the answer to their questions.

Have fun,

Ben