Accessing waveform chart history collected via DAQmx

Hello, I'm collecting voltage data using DAQmx and I'm displaying the data using a waveform chart. At the end of the acquisition I would like to access the entire data set stored in the chart but when I attempt to do so using a History Data property node, it only gives me the data that was collected in the last chart update, not all of the data stored in the chart. Attached is a copy of the program, which is simply the Continuous Analog Input example. Any suggestions? Thanks!
Attachments:
Jeffs_Voltage - Continuous Input.vi ‏80 KB

Data Flow. You have no clue when that chart history will be read. You need to force it to read after the acquisition is complete. Using the error wire to force the data dependancy is a good way to do it.
How long are you acquiring the data for? If much more than a few seconds, I would use that logging feature to stream the data to a TDMS file and then you can just read the resulting file.
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Similar Messages

Multiple Axis Waveform Chart History?

Hello Everyone,
Recently I have been working on increasing my capabilities with waveform charts. I am plotting 3 signals on 3 seperate axis. I'd like to be able to transfer the plot history from one chart to another via property nodes. The problem is, only 2 of my signals are making it through, and I'm not sure why.
For a little background why my code is structured the way it is, I followed an example from here:
Pausing Charts
Basically I want to be able to zoom in on the chart while the program is running. By hitting pause, the data is transfered to another plot that isn't being updated. Again, only 2 of my signals are making it through, and I'm not sure if there is a property node I'm missing.
Any help would be appreciated, the VI is attached below.
Thanks,
Alex
Attachments:
Chart Test.vi ‏39 KB

For some reason the "Brake Temp" plot's color was screwed up. If you look at the legend it looks like it's black. However, changing the plot's color doesn't seem to have any effect. If you just recreate the "pause" graph by copying the "Waveform Chart" indicator then it will work.
Suggestion: look into the Event Structure.

Clear waveform chart history if dynamic 1D data is used

I am new to Labview and am using a Waveform Chart. To clear this I need to supply an empty array. I have done this with scalar inputs, but in this present case, the input to the chart is a bundle of 1-D array of dynamic data. I cannot figure out how to create a suitable empty array of type 1D array of dynamic data to initialize the plot (wire to the History).
It seems like there should be a better (easier) way of clearing the plot...
Thanks for any ideas.
Solved!
Go to Solution.

Hi rockybooth,
right click on the connector to the history property and select "create constant". You should get what you need.
Hope it helps.
Mike

Using waveform chart to collect data

Hello,
I am a new user to labview, however I have been using it for a while now.
I have a simple problem.
My model runs a drive cycle for 1400 secs.
I want to record data for a sample rate of 1 sec.
However, When I try to run the model and export it to excel it shows data for a sample rate of 0.1 seconds. How can I change that?
Also, what can be the maximum buffer size of the waveform chart?

Hey govindgoal,
The max buffer size is pretty massive so don't worry about that. I would post your code or at least the part which is recording the data for people to help debug. It would seem however that you have some timing issues with your application.
Regards
Andy
"To 'G' and not to 'C', this is not a question!"

Saving array data from a waveform chart

I am using a CRIO 9004 and a 9237 bridge module to measure some strains from strain gauges. I've got one timed loop that reads the DMA FIFO and puts the arrays of values (16 data points, 4 per channel) into a queue. In the consumer timed loop a For loop scales the binary data, auto indexes it into arrays, then the arrays are merged into a 2D array for the four channels displayed on a waveform chart . Everytime the consumer loop runs it indexes 4 data points (per channel) yet the waveform chart plots them in a consecutive manner and doesn't overwrite the previous four. If I convert the arrays to waveform arrays I don't see anything on the waveform chart.
If I pass the 2D array of data to a array indicator inside or outside the consumer loop I get only 16 data points. I want to save the information that appears on the waveform chart after the consumer loop but because I'm not using waveform data type I can't use the write waveforms to file vi. The waveform chart history buffer has been set to 195360.
Idealy we will run the four channels for 120 seconds charting the data and saving the data. The minimum data rate is 1613kS/s (403 per channel) The data can be saved after the loops have finished gathering and processing or while they are running. I noticed when I tried to write to TDMS it slowed the consumer down. Same thing if I use a shift register with the volume of data.
I suspect I'm not sending data to the chart in the correct manner ( usualy takes two attempts to "clear chart" using shortcut menu). I'm not too familiar with timed loops /producer consumer loops and just tried to put something together based on examples.
I've attached my host vi and front panel screenshot.

Hope they appear attached this time.
Attachments:
Basic DMA (Host).vi ‏444 KB
screenshot2.jpg ‏113 KB

Strip Chart history buffer

Hallo,
I have a little crazy question - is there some possibility to access strip chart history buffer?
I'm just lazy to develop data circular buffer management ....
Thanks a lot for any hint!
George

Hi, Evan,
thanks for reply.
My idea is use already used memory of the strip chart (not duplicate the amount of allocating memory) - mainly to export recorded traces - e.g. when user decided: "this is interesting - let's make some analysis of this, maybe at home".
The Strip Chart hasn't simple solution to use cursors - and by exporting the history buffer (traces) to some file / array is quite easy use standard graph with cursors etc.
Of course, the cicular buffer is OK.
George

How to get the history(datapoints) of 32 waveform-charts which are in one cluster?

Thanks in advance. I would like to handle up to 32 waveform-charts by using a cluster. My problem is that the datapoints of their history has to be saved if a particular event occures. How can I get the character-node for the history of a waveform-chart inside the cluster?

I'm not certain what you are asking, but here's a suggestion. On the front panel, you can pop-up (right-click) on a waveform chart within a cluster and create a property-node (for the history), which can be manipulated as you desire on the diagram.

Why does AI Read(Asynchronous).vi cause the waveform chart to not display any history ?

I trying to create a strip chart for 16 channels that will require displaying 10-20 minutes of data.It also starts a separate vi to set gains and offsets while displaying the data. Using AI Read.vi uses 100% of the CPU so the second vi does not run. But using AI Read (async).vi allows the second vi to run, but causes the waveform chart to not display the history? I'm using LabView version 6.0.2.

Hi Waynes World,
I have a couple of questions that may help us solve this issue...
1) If you are modifying one of our example programs, which one did you start with?
2) What kind of analog input are you doing? Buffered? Finite or continuous?
3) Have you tried increasing the buffer size of the strip chart? This will allow the chart to store more data in it.
4) When you use the Async VI, and when you are using the other, can you describe how the strip chart is showing the data... does the data in the chart keep growing and growing... or does it clear itself and start over when the pine reaches the end?
I think this issue is rooted in how the buffer is being used with the two different AI Reads and how it returns data to the chart.
On a side note, have you considered upgrading to a newer version of LabVIEW? Our latest versions of LabVIEW come with many new features and it is signifigantly easier to use.

Buffered Viewing of Waveform Charts?

We're acquiring very large data sets, using 'Cont Acq&Graph (buffered).vi' as sort of a template for the data acquisition.
The resulting files are much larger than physical RAM, but the researchers are only interested in small parts of the collected data: The researchers need to be able to go back over the data run, choose a few seconds here and there for permanent archiving, and then discard the rest of the data.
Because the size of the data run is larger than the physical RAM in the computer, the 'viewing and extracting' VI can read from file and display to screen [via a Waveform chart] only a few seconds of data at a time. Because hard drive access time is so much slower than RAM access time, I'd like to buffer this data view
[just a little to the left and a little to the right], so that if the researcher chooses to move a little bit back in time, or a little bit forward in time, the data will [probably] be cached in RAM and the VI won't have to make a relatively slow call to disk.
Of course, the art of buffering rapidly degenerates into a PhD level computer science mess [owing to not necessarily contiguous runs of not necessarily ordered data], and I really don't feel like writing a buffering algorithm from the ground up [especially not in a visual language like LabView].
I was hoping maybe the Waveform Chart might have some capability to perform [not necessarily contiguous and not necessarily ordered] buffering. Does anyone know if this is possible, or am I asking for too much?
Or should I just rely on the operating system [soft caching] and/or the disk controller/disk [hard caching] to perform my buffering [caching] for me?
Or do the standard LabView byte stream disk reading VIs perform thei
r own [not necessarily contiguous, not necessarily ordered] buffering?"

The waveform chart does keep a history of the data passed to it. You can set the buffer length at program time. When you read the data (the data desired + buffered regions) from disk you can polulate the history by writing to the history property node. You can then postion the data in the chart with a property node. Be sure to make the x scroll bar visible. (right click on the chart >> visible items >> x scroll bar). I attached a VI in LV 7 to demonstrate.
There is no telling if relying on the OS and hard disk controller will give you desired performance. I do not believe the byte stream functions in LabVIEW do any sort of buffering either.
You will have to experiment to see what works. If you as the user cannot tell between experiments then
chances are the implementation does not matter.
By the way, LabVIEW does not support abstract data structures because it does not expose pointer operations to the programmer.
Attachments:
Untitled.vi ‏24 KB

How to take waveform chart data and put it into an array

Hello all,
I am new to programming in Labview, and am learning basically by watching youtube video and such. My question is how to take a set of random data that I have written code for and linked to a waveform chart, and put the data into an array so I can calculate the mean of the data set. If there is an easier way to calculate the mean of the data set I am all ears, but I need to be able to display the mean on the front panel each time the code is run. I have attached a file of my code.
Thanks
Attachments:
CA1.vi ‏11 KB

Welcome.
If you have not done so, look at the on-line tutorials on Getting Started with LabVIEW on the NI web site.
A chart has a property known as History which retains some previous values. You can get access to the the History property by popping up on the block diagram terminal of the chart and selecting Create >> Property Node. Note that the history length can be set via a pop up menu. The default length is 1024.
Other comments: When you know the number of iteration in advance you should use a for loop rather than the while loop.
You can also use an autoindexing tunnel at the boundary of the loop to create an array. It only contains the values from the current run, unlike the chart history which can retain values between runs (as long as the VI remains in memory). Watch the two Mean indicators as you run this VI several times.
The error wire is to assure that the history property node runs after the loop. Disconnect the wire and watch the Mean and Mean 2 indicators carefully.
The Wait is to slow things down a bit so that you can see what is happening.
Lynn
Attachments:
CA1.2.vi ‏11 KB

Display Data on waveform chart or XY graph over a long period of time

Display Data on waveform chart or XY graph over a long period of time
Can anyone help?
I am acquiring data from an Ni DAQ card with the following parameters - sample rate = 12800, number of samples = 4096. I want to extract order information so as to track changes in the amplitudes of certain frequency harmonics. So I use the sound and vibration toolkit to extract this information as shown in the attached Vi. I will like to plot the resulting amplitudes against real-time starting at the time the Vi was run. I really want the display to show these changes over long periods (eg. days, months and even years).
Problem.
I have tried to plot the Y component of the resulting magnitude for a given order on a waveform chart. My choice of the waveform chart is because I also want to display alarm limits (using the mask and limit vi) (I can't have these lines displayed on an XY graph plot). I tried adjusting the scale offset using the property node and setting the offset to current time. However, the display on the X-axis can only show a span of 2 minutes as will be seen when you run the attached vi. I want the time display on the x-axis to be over a period of days, months and even years. Is there a way to set the maximum scale on the x-axis to be say a year or so in future.
I really want the display to be like the one in in the second attachment.
Attached is a sample VI created using an Ni USB 9234 DAQ card. Any card will do but I am only getting the signal from one channel for this example
I will appreciate any help that can be given to me.
Thanks
Attachments:
Real-Time Graph Display.vi ‏170 KB
Sampe screen1.doc ‏37 KB

Long term testing can be tricky- and we'l get into that later. Lets start with the basics that you have wrong.
The vi as you have constructed it has only one memory element, the chart history length (default is 1024.)
You can change the number of points the Chart will remember by Right-clicking the chart an select Chart History Length from the menu.
But for a long term test - and one where you want to REMEMBER the first value you need a memeory element that is independant of the application. Your PC WILL loose power or need to be rebooted eventually. Heck it might even need to be replaced! you really need to store your data in a file. Preferablly in a file that is backed-up on a regular basis so you don't lose every point of data if the PC dies. It realy hurts when you have to restart a 2yr test because you've lost the 18months of data you collected.
For an application like this I would seperate my "collection" and "Evaluation" operations.
Have one vi that takes the reading and writes it to a file at a configurable rate You may want 1reading per minute for seveal days then 1 per hour for a few weeks- then maybe only once or twice a week for the next couple of years since you are looking for LONG TERM stability. having too much data to evaluate can take a lot of digging to find the few things that interest you (but always take more that you think you need)
Have another utility that COPIES the files, reads them and displays the data you are interested in that day. The data you want to look at won't change over time HOWEVER, you WILL want to analize it in different ways depending on what the data trends look like. Having seperate routines for collection and display allows you to update the display style and analisys without even stopping the collection vi (much less editing the vi)
Jeff

How can I display more than 1 loop iteraction in a waveform chart?

Using DAQmx, I am inputting a signal at a rate of 10k with 1k samples inside a while loop. I want the first 3 seconds of data to display on a waveform chart without having to change the rate or number of samples. Is there a way to stop the waveform chart from clearing after every loop iteration so that I can display more than 0.1sec of data? Thank you for any help you can provide!

The default history length of a chart is 1024. To make it longer is a right click option.

How to set maximum number of data points displayed on waveform chart?

I have a waveform chart set to x-autoscale, but after about 1000 data points, it begins to scroll again. How can I display all of the data points being collected, say 2000 points?

Right click on the chart and select Chart History Length. Enter the value that you need. The maximum is 2147483647 points.

Labview absolute time waveform chart to excel

Hi everyone, I have a bit confusing on absolute time waveform chart. My problem is when I want to export to excel, the data duplicate nearly 30 times for each second. My project is about collect temperature from serial port and plot it in waveform chart, and I want to view history data in excel.
Anyone can help to solve my question? I attached my vi here..
Thank you so much..
Attachments:
NEW FINAL1.vi ‏96 KB
snap.PNG ‏11 KB

You are getting such a large number of readings because your VI has no timing control in it, if you simply add in a delay somewhere of maybe migrate to an event structure with a timeout then you can control the number of readings that are taken per second.

Waveform chart X-Axis reverses itself when upper limit is edited in Absolute Time - problem may be linked to Timestamp Control?

I've seen this problem for some time now, and it still exists in the Silver toolset Waveform Chart in LV 2012. If the chart is in strip mode, and you edit the upper limit value to a point in the future, the X-Axis will invert (higher values/ later time to the left), to the limit of the Chart History length. This happens whether the chart is active (logging data on a compiled executable) or even when in design mode, though it's more consistent when there's data in the chart. It's not history length related as far as I can tell, as I set the length to 7 days of sampling @ 1-second intervals (605K), and it happens when I try to set the end time to an hour in the future with only a few minutes of data collected - suddenly the right Absolute Time becomes the time my last sample point was collected, while the left Absolute Time becomes nearly 7 days in the future (so neither end point is what I was setting it to).
It's nice that the chart gives the option of editing the limits, but as such, it's important that they work as you would expect them to.
Also - until this is addressed, is there a way to lock it against editing? Until a fix is made, my workaround is to put a transparent button over the range start & end points, and a transparent flat rectangle above all other mid-range points, and pop-up a data entry form with a Timestamp control to allow editing. Unfortunately, this doesn't work as I would expect, as typing "11 AM" in the Timestamp control over a prior value of say "10:05:34.232 AM" ends up becoming "11:05:34.232 AM" instead. ??? Another error - or is this by design? If it's by design, is there an option to make it behave as I would prefer (11 AM = 11:00:00.000 AM), as Excel behaves with timestamps? I can't help but suspect this may be linked to the chart axis issue.
Also - I just built a simplified chart modeled somewhat on my current project, and could not get this to recur. BUT... had the strangest thing happen: My sample data was generated using the Trig functions for Sine and Cosine, and at one point my waveforms distorted on the display, so I'm attaching that here plus the simplified chart project.
Last - my system is LV 2012 on Win7 Pro-x64.
Thanks!
Erik
Attachments:
Chart data distorted.png ‏45 KB
Waveform Chart Flaw.zip ‏17 KB

I am not so sure that this is a bug, and I have not been able to reproduce this behavior that you are describing.
But you can lock it from editing by right-clicking on the graph and go to Properties>>Appearance>>Enabled State --> Disabled
Also, word of advice for the future: You will get more replies from the community with shorter posts and keeping it to one question per post. Summarize what the issue is, and put the detailed documentation and instructions to reproduce in the actual VI.
Huntington W
National Instruments
Applications Engineer
***Don't forget to give Kudos and Accepted as Solution where it is deserved***

Accessing waveform chart history collected via DAQmx

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