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my timebase does not scroll (in my voltage measurements)

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I have a 5v DC pot connected to my 6008 USB  DAQ. In labVIEW when I run it I get my voltage output as expected but the timebase does not scroll it remains fixed. When I change the axes scales the output voltage still only varies over the first second only. Does anyone know what is wrong ?
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Message 1 of 16
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Each time you write to the graph, you are sending new data and obviously there would be no scrolling since it would always display the same number of samples. That's just understanding the basics of how a graph works. If you want actual time on the x axis and you are using a waveform or dynamic data, the timestamps on the graph will change if you unchecked the Ignore Timestamps (right click on graph to see this option).

 

If you want to append new signals to old, then you should use the chart and set the history length to the number of samples you want to show at one time.

Message Edited by Dennis Knutson on 06-17-2009 10:01 PM
Message 2 of 16
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hi thanks for your reply. But I have triede unchecking the "Ignore time stamp" but to no avail. Tried various x-scale properties but still only shows the 1st second of data. I was expectign a display to look like it does in test panels on MAX. U mentioned setting the time hsitory of data to show to which new data samples are appended. I cant find any options for this. Please give further details
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Please provide some more information. If you aren't using a chart, there is no history to set. If you are using a graph, it will only display the current acquisition.

 

Attach the VI you've written so somone can see what is going on.

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Hi,

 

Thanks again for your reply. I wasing using a waveform graph instead of chart. I've noew used a chart and the timbase scrolls ALMOST as required. Would really like teach run to start at time 0.0. However, I've been through the various options, absolute time, relative , time, SI notation etc and it will only either display time as in attachment (absolute time) or relative time from some very large number i.e start at some number like 392356743 and then scroll from there. How do I get it to start at 0.0 on each run and scroll from there onwards.

 

I've attached vi in *.doc

 

 

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No, you did not attach a VI. You attached a proprietarty file format that probably contains an image of your VI. Not at all the same thing and absolutely worthless for running the VI. I don't have the latest and greatest version of Word anyway and have no intention of getting it or even a viewer for it. Hopfeully someone else will respond.
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Ok, 2 Vis attached. Please ignore all unattached elements ...they're intended for later use. THe output of my DAQ is attached to the Chart "Voltage: Wheel Pot 3" in the "elevator_vi"

 

 

I have an additional issue as well as the time base of this Chart. THe attached "gearing_vi" is the same as the elevator_vi but I now want to display a stacked multiple plot chart with 3 inputs using the bundle function but I cannot connect the output of the bundle to the chart. I get an error message telling me the two terminals have different data types.

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Solution
Accepted by topic author esctosh

I don't think you can ignore the timestamp that is part of dynamic data. I never use dynamic data and I hope I never am placed in a situation where I have to.

 

One possibly fix for the elevator VI is in the attachment. Since you have wired the data to some scalar indicators, it soes not seem like you care about 1000 samples so I used a Mean function to get a scalar with at least some meaninig. I thne converted to an actual scalar.

 

If you want to stick to dynamic data, then you cannot use the bundle function in the gearing VI. The correct function would be the Merge Signals function.

Message 8 of 16
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Hi thanks again for your reply. That seems to define the starting reference point. You have suggested that as Im using dynamic data I'm pretty much bound to the timestamp which is why I cant have an x-axis (time) that starts at a 0.0 and iterates relative to this. I guess I'll just have to accept that.

 

My input to my DAQ is a linear rod potentiometer ( with 200mm full scale defelection). So it will dynamically output a voltage 0 - 5v for 0 - 200mm of displacement of the rod potentiometer. To put this in context the pot swill be connected to (for example) the column/elevator on an aircraft. So it will output a voltage linearly proportional to the displacement of the column/surface. Is there any other way of doing this without "dynamic data" ? As you say you have never used dynamic data and being far more experienced than me in using LabVIEW was wondering if  there was an alternative for the type of configuratiom I'm using ?

 

I've attached my data scalar constants in my block diagram to convert the output voltage from potentiometer (that is input into AI0 of the DAQ) into a potentiometer displacement (0 - 200mm) or wheel angle (-180 deg to 180deg), for example, as illustrated in my front panel. I dont know of any other way of doing this - Since the pot is linear (1v per 40mm of displacement) I just scaled the voltage to provide a representation of pot displacment. Is this a sensible thing to do ? The use of the scalars doesn't diminish my need for a high sample rate. I think I still need as high a sample rate as possible (1000hz the max for 6008 DAQ ?) as inceptor input could be quite rapid and I need to ensure I get as many samples as possible to measure the relative gearing between inceptor and surface.

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Message 9 of 16
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The problem with dynamic data and wiring to a scalar indicator is what does the value represent? Is it the last value of the 1000 you've scanned or the first? I really have no idea and have no intention of finding out since I refuse to use dynamic data. That is why I added the mean function. At least that makes some useage out of all of the 1000 values you've acquired instead of 1 out of a 1000.
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