How to update the absolute time value in waveform chart for labview 6i?

[Saby]

Hey there,
I'm developing a control system using labview 6i on win 2000 os.I'm receiving the sensor data every minute and i want to display the data on a waveform chart with absolute time scale on x-axes. I'm using the property nodes for the offset, multiplier and maximum values putting them outside the while loop and giving them input using get date/time in seconds function. the problem is that the time doesn't gets updated w/ refernce to the computer time and after a certain period the time shown on x-axes lags by several hours. any advise?

[Ben]

Posting an example ussually help us nail these types of issues fast.

I am therfore forced to guess.

Do you have your code written such that the scale operations occur before the loop?

The next thing I have to suspect (not being able to see your code) is if your dt is correct. If your dt is larger than what the chart is set for, then the time will fall behind.

I have included an image showing how the chart can be used to show multiple sample rate plots such that the t0 of the readings are used to control how the readings are displayed. This example uses waveform data types (I believe they were available back in 6i). It should serve as a guide to do what you want.

I suggest you start by recreating the demo and play with it until you have what
you will need in your app.

The beauty of this method is it lets you use the chart to plot signals acquired at different frequecies and plot them all together.

reply to this answer if you have questions,

Ben


Ben Rayner
Certified LabVIEW Developer
www.DSAutomation.com

[Saby]

Thanks for the help, Ben. I'm attaching the sample code. Please let me know where i'm getting it wrong.

- Saby

[Ben]

Look at "offset and multipler" (still under X-Scale).

Also sequnce your code such that you set the time BEFORE the loop starts.

Ben