Chart/Graph for time-stamped data 
Author Message
 Chart/Graph for time-stamped data

I want to display multi-pseudrealtime-x values from serial port with
its correct time stamps. Serial communication frequncy is about 10 Hz
but not uniform, changing 1-20Hz. So I cannot use standard chart. I
try to use x-y graph with scroll by range property, but it is awully
dizzy. How I can display them?


Mon, 09 Aug 2004 20:38:43 GMT  
 Chart/Graph for time-stamped data
How about adding a polling routine that only examines the serial input
buffer once every 10ms?  That way all of your data will be displayed
with a 10ms resolution and in 10ms chunks.  If there are multiple data
points in the buffer, then you can average them.  If there are no
points, then you can skip that time stamp or adjust your program so
you'll get at least one data point per sample.  Of course this will
move away from 'realtime', but it may be acceptable depending on what
you are going to be doing with the data (visual only, logging, etc.).

+Chris



Mon, 09 Aug 2004 22:40:04 GMT  
 Chart/Graph for time-stamped data
Thanks for your advise. I have tried that, but it displays diffrent
waveform from that of x-y graph. I'd like to display correct waveform.


Tue, 10 Aug 2004 07:23:35 GMT  
 Chart/Graph for time-stamped data
What is the exact waveform you would like to display?  You mentioned
data and timestamp, and I envisioned a scrolling stripchart.  Is this
what you had in mind as well?  What are your x and y axis?


Tue, 10 Aug 2004 10:38:45 GMT  
 Chart/Graph for time-stamped data
What I want to display are Speed command for a divice and its actual
speed sent from the control computer other than labview computor. As
the control computer gives priority to the real time control, serail
communication timing varies time to time.


Tue, 10 Aug 2004 12:04:14 GMT  
 Chart/Graph for time-stamped data

Quote:
> What I want to display are Speed command for a divice and its actual
> speed sent from the control computer other than Labview computor. As
> the control computer gives priority to the real time control, serail
> communication timing varies time to time.

You don't mention a version number.  If you can build the points into
a waveform, then the chart will be given timestamped points and will
correctly plot them.  This is the only way to timestamp points for a
chart and all other methods assume that dT is constant between points.
If you don't have LV6, you don't have waveforms and your best bet is to
use the XY graph.  There are VIs in the examples/general/graph folder
for making an XY chart.

Greg McKaskle



Wed, 11 Aug 2004 11:57:23 GMT  
 Chart/Graph for time-stamped data
I cannot open the sample because my LabVIEW is version 6.0.2. But I
look in real-time chart.vi of 6.0.2, it seems that dt can be
configurable at start-up only.... What I want to do is dt can
configurable for everytime.


Fri, 13 Aug 2004 07:48:35 GMT  
 Chart/Graph for time-stamped data
My LabVIEW version is 6.0.2. Will you inform me how to change dt
everytime?


Fri, 13 Aug 2004 07:50:22 GMT  
 Chart/Graph for time-stamped data

Quote:
> My LabVIEW version is 6.0.2. Will you inform me how to change dt
> everytime?

The key is to make the basic element a waveform rather than a scalar
number.  If you currently have a scalar double wired to your chart, go
to the waveform palette and drop a Build Waveform node.  This will allow
you to wire up a timestamp and a deltaTime.  For single points, only the
timestamp is used.  Doing this, you now have timestamped points and the
chart will place them on the time scale based upon this value.  There
are a few assumptions such as -- time marches forward.  A timestamp
before others written to the chart will clear the chart assuming that
you are starting over again.

If you are currently updating the chart with an array, you can drop the
same node and give the amplitudes a timestamp as well as a dT to
describe the time between the elements of the array.

If you currently have a cluster wired to the chart, take the point of
each cluster, make a waveform, and build an array of the waveforms.

If you currently have an array of clusters, then you will want to build
an array of waveforms similarly.

If this description isn't enough help, you might want to look at the
graph examples.

Greg McKaskle



Sat, 14 Aug 2004 10:30:05 GMT  
 Chart/Graph for time-stamped data
As far as I understand, dt is a constant along the time. In my
application, dt between Xi and Xi+1 varies along the time. Can I use
build waveform?


Sat, 14 Aug 2004 12:05:25 GMT  
 Chart/Graph for time-stamped data

Quote:
> As far as I understand, dt is a constant along the time. In my
> application, dt between Xi and Xi+1 varies along the time. Can I use
> build waveform?

Yes.  In a waveform, the timestamp is the time of the first point in the
array of amplitudes.  The dt value is used to compute the time of
subsequent points as time[n]= T0 + dt*(n-1).  If you have single point
waveforms, the dT doesn't matter, only T0.

Greg McKaskle



Sun, 15 Aug 2004 11:26:26 GMT  
 Chart/Graph for time-stamped data
Thank you. Now I understand that the realtime data of variable dt can
be displayed in X-Y Graph only and if adapting scroll to it, we shall
caught by its too dizzy appearnce.
Am I correct?


Sun, 15 Aug 2004 12:59:03 GMT  
 
 [ 12 post ] 

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