Waveform chart time sometimes decreases

I have a waveform chart with three plots vs time with update mode set to strip chart. It is demonstrating strange behavior which I have never noticed before. The time sample numbers at the extents of the axis sometimes decrease and the plots shift to the right instead of always left as I have always expected. Can anyone offer a plausible reason why this situation might occur?

the following applies only to charts that are Waveform data types, otherwise disregard.
Check the validity of the t0 values in the WF. If the timestamp is earler than the latest value plotted, the chart will reset.
Ben
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Waveform chart time axis is not matching the waveform data

So here an interesting conundrum I hope you might be able to help me with...
My VI has waveform data sent to a chart, though the data is not being plotted against the current time. Rather, it is being plotted starting way back in the reference time (way back in 1903). I don't understand why this is happening. When I build the waveform, I use the "Get Date/Time in Seconds" function outside the while loop and feed that into my "Build Waveform" Function as the t0 value. My dt value is 0.05 (20 Hz) and then I feed in my array of data in the Y input. Any ideas why the chart is plotting this data over 100 years ago? Thanks!
Andrew

Hiii, Ronin
Here is your solution.
By default, waveform charts and graphs display the absolute time at time 0 as 7:00:00 PM, 12/31/1903 on a Windows based system. Property nodes can be used to get the correct absolute time to display on the x-axis of the waveform chart.
First, right click the chart on the front panel and select X Scale >> Formatting. Then set the format to Absolute Time.
Create a property node for the waveform chart by right-clicking on the chart on the block diagram and selecting Create >> Property Node. Expand the property node to display two properties. Select the Format property and the Offset property. The Format property is located under X-Scale >> Format and Precision >> Format, and the Offset property can be found under X-Scale >> Offset and Multiplier >> Offset. Right click on the property node and select Change All to Write.
For the Format property, the context help shows that there are multiple inputs to this property. Wire in a value of 7 to set the format to Time and Date.For the Offset property, first wire the output of the Get Data/Time in Seconds VI to the input of the To Double Precision Float VI. Then wire the output of the To Double Precision Float VI to the Offset property.
In addition, if you know the number of data points plotted to the chart per second, you can set the Multiplier property located under X-Scale >> Offset and Multiplier >> Multiplier. If there are x data points generated per second, wire in a value of 1/x to the Multiplier property. A simple example program "Chart with Timestamp" that demonstrates how to do that is attached.
Thanks,
Nishant
Attachments:
Chart with Timestamp.vi ‏36 KB

Question about waveform chart time scale

Hello,
I have question regarding to time scale on my chart, I want it to show the actual measured time, for example from 0-30 seconds, but instead my minimum value is 302654789854 . Please help me to fix it.
Regards ,
Stella Deheryan

You can modify the way the time is displayed on the axis by right clicking the chart and selecting properties. On the display format tab, select relative time. This should show the X-axis scale as HH:MM. Or pick any other type of formatting you want.
Best Regards
Michiel
Applications Engineer
NI Belgium
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Problem with waveform chart: time scale does not show time correctly

Hello,
I have some problems with a chart.
I want to display some data and the time between two single data can vary. It is something between 50ms and 500 ms.
The problems I have:
1. The time is not shown correctly in the chart (allways 2:00:10 instead of the current time)
2. the data points in the chart have a distance of 1 s (x-scale). That is not correct.
I have tried several things but I thinkt I am on the wrong track.
Could you please help me?
Johannes
LabVIEW 7.1 (!)
Message Edited by johanneshoer on 10-14-2009 04:26 AM
Greetings Johannes
Using LabVIEW 7.1 and 2009 recently
Solved!
Go to Solution.
Attachments:
Chart Test.vi ‏55 KB

I have modifierd the vi again.
Now it looks much better.
I have a data array and the last 10 seconds of the data are displayed.
The array size is maximum 150 and that is more than I need to display. If new data is inserted, the oldest gets deleted.
I wonder if this style is efficient?
The time is stil not displayed correctly in the graph. Why does it always show 2:00:00 ?
Johanens
LabVIEW 7.1
Greetings Johannes
Using LabVIEW 7.1 and 2009 recently
Attachments:
Chart Test 3.vi ‏57 KB

How do i set the time frame of a waveform chart programmatically to be a 30 sec window or a 24 hour window

i'm using LV7.0 and what i need to do is to be able to set the time frame or range of a waveform chart programmatically before i start taking and plotting data. sometimes this window needs to be 30s wide and sometimes it needs to be 24 hrs wide. (in the first reference, i need the chart to fill up with 30s of historical data then the whole chart scrolls with each new data point). the data acquisition records data at a rate of once per second. i've tried to use the chart properties of XScale.offset, XScale.Range.Minimum and XScale.Range.Maximum but no matter what i do the time-stamp on the x-axis is always "00:00:00 PM" and "MM/DD/YYYY" even though values are seen being plotted on the right side of the chart as expected.
Attachments:
BX0265 ShelfLife DAQmx.vi ‏120 KB

Okay, there seems to be some confusion here -- the X axis values are of type double, but they can be represented in the HH:MMS MMD:YYYY format if you want in which case it interprets the floating point as the number of seconds since 6pm Dec 31, 1903.
You can programmatically set this value using the XScale.Minimum and XScale.Maximum properties, but note that if you wire a waveform to the chart after setting these values the t0 parameter will override what you set using the property node for XScale.Minimum. If instead you leave the t0 parameter empty you can use the XScale.Offset property and wire the same value in that you wire to XScale.Minimum. Changing the amount you add to XScale.Minmum to obtain what you wire into XScale.Maximum will determine the time window size.
Doug M
Applications Engineer
National Instruments
For those unfamiliar with NBC's The Office, my icon is NOT a picture of me

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 do I add a time stamp to the moving "Major Grid Lines" of a Waveform Chart?

Hello
I am using LV 8.5.1
I am using a Waveform Chart and I have turned on the "Major Grid LInes" using the properties tab of my waveform chart. (properties-->scale->grid lines)
When the code executes, I want to attach a time stamp to each moving yellow grid line.
So as the grid lines move from right to left, there is an associated time stamp for each.
Can someone help!
thanks
J
Solved!
Go to Solution.
Attachments:
how do I add time to the yellow grid lines.vi ‏16 KB

hova2010,
If you right click on your graph and go to X Scale >> Style >> and then choose one of the 3 styles on the far left you shoul see timestamps for those grid lines.
Ben Sisney
FlexRIO V&V Engineer
National Instruments

How do you set the size / bounds of a waveform chart at run time?

I have a plot area that I would like to fill with as many waveform charts as the user specifies (at run time). The "bounds" property is read only and I haven't noticed an additional "size" property for a waveform chart as there is for a button. Is there a way to set the size of a waveform chart at run time, and if not, why not? (Labview 6.1)

Look at it a little more carefully, I suspect that your assumption is only half wrong. The property does only resize the plot area--LV resizes the frame to fit the resized plot on it's own.
You'll need to bear this in mind when you're figuring-out what size to set the property to.
Mike...
Certified Professional Instructor
Certified LabVIEW Architect
LabVIEW Champion
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How to show two different plots with current system time and date on waveform chart

I am using one waveform chart to display the more than one value continiously. The data are comming properly but i am not getting my system (pc) time and date on x axis. It is showing default date and time (i.e.01/01/1904 5:30:45). Please give me suggestions to display the real time and date on x axis of waveform chart.

How does your data look like? Do you graph waveform data types, dynamic data, or plain arrays/clustes? In the case of plain arrays, you need to set x0 to the absolute start time of your data, e.g. with a property node.
I you would attach your code (or an image) we could offer more specific advice. There are too many possibilities.
LabVIEW Champion . Do more with less code and in less time .

Only first plot of waveform chart has run-time menu

Hello again all you helpful forum-goers!
My multi-plot waveform chart is working decently well, but now for some reason only the first plot in the plot legend displays a run-time customization menu when I click on it while the VI is running (allowing me to select the plot color, etc.). All the other plots do nothing when I click on them. I do not have any mouse-down events or filter events of any kind in my VI. I programmatically set the number of plots and the size of the plot legend, along with each plot's name, y index, and color. Any ideas as to what might be going on?
Thanks a bunch as always!
-Joe
Solved!
Go to Solution.

Okay, hopefully this will help get some more thoughts / answers flowing. I've copied my strip chart from my actual VI into a test VI, and it still exhibits the problem. On the other hand, I have created a new strip chart from scratch, and it works fine. I have attached both VIs here for you to see. My guess is that some property of the first chart is set incorrectly or something, but I cannot figure out which one (and there are so many!).
Any assistance you can give would be appreciated. The challenge is to get the chart in the first VI working (plots other than the first responding to a mouse click to change their color or other attributes), via changing some attribute of the chart (and being able to tell me which one you changed!).
Thank you again for anyone who can look into this.
-Joe
Attachments:
Test StripChart color selection not working.vi ‏17 KB
Test StripChart color selection working.vi ‏12 KB

My waveform chart is suppose to be with respect to time but I've noticed it is plotted with respect to the number of times through my VI

I was under the assumption that waveform charts in LabVIEW 6i atomaticly displayed wired data with respect to time in seconds. However, I noticed that my chart plots data with respect to the number of data points my VI has generated. Is there anyway to fix this so that the chart actually plots vs. time. I've attached VI. The CIN is to a Computerboards Inc, thermocouple. Any help would be appreciated.
Attachments:
tepTInScan.VI ‏73 KB

It appears that the chart is set to display relative time but since you don't have the acquisition in any kind of a loop, your relative time is pretty meaningless. You've got the dX of the chart set to be one, so yeah, at the beginning, the x scale numbers are going to be the same as the number of aquisitions until you've run it more than 60 times. At this point, you'll see the x scale show minutes and seconds. If you want absolute time for the x scale, look at the examples Real-Time Chart.vi or Variable-Time Chart XY.vi.

Time stamp on Waveform Charts

I'm making an application where I sample data every 5 seconds. I use the Time Delay VI to obtain the sampling interval, and then set the chart options using chart properties/format and precision/relative time. The chart is adding a point every 5 secs as it should, scale looks ok. However, the time scale on the graph is incrementing only one second at the time (although actual time elapsed is 5 secs). The log file gives the time stamps just as it should. Is there a way to make the waveform chart give the real time (other than the obvious solution of sampling 1 pt/sec)?

I'm just directly passing scalar values to the chart. The total acquisition time is about an hour, and the idea is to display data as they vary with time.

Waveform Chart - How to set X scale time.

I have a Waveform chart (v6.1) and I want it to display 30 seconds of data. What is the correlation between the Time History buffer and the Time inputed on the X-scale. The X-scale format is set to Relative Time. I set the initial time to 0:00. The input data is coming in at 20 samples/sec also. How do I set up the chart to show only 30 sec of data.

You can turn Auto scale off and set the left value to 0 and right value to 0:30.
A second method is to set the chart history length to 600 (20 samples per second * 30 seconds). Setting the chart history length can only be done at design time.
Waldemar
Waldemar
Using 7.1.1, 8.5.1, 8.6.1, 2009 on XP and RT
Don't forget to give Kudos to good answers and/or questions

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.

Want a constant time axis in waveform chart

hello,
my time axis in waveform chart is changing .how can i keep it constant say 1-100 .the whole point of this is to make waveform chart luk like a CRO.please need help.
thanks in advace
naveen.rabelli

I don't think what you're asking for is possible, due to the nature of the chart - it accepts Y values and inserts the X value automatically. Offhand, I can think of 3 solutions -
The bad one - constantly change the offset by moving it backwords. You will probably have flickering.
The workaround one - Paste a text box over the first number saying 1 and another over the second number saying 100.
The probably most correct one - Use a XY graph. Just have a 1D array of 100 elements and append it to a second 1D array with 1..100. Wire the 2D array into the graph terminal.
Try to take over the world!

Waveform chart time sometimes decreases

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