Moving Time Graph with DAQ?

[sophie83]

Hi, I am trying to run my program using the DAQ. Basically I am trying to display a sine wave on a graph.  I would like the sine wave to move with time, and the time axis changing so like a moving time graph.  However,  When I run the program, it displays the signal perfectly however the x -axis (time) does not change, when I replace the graph with a chart, the time axis changes ( but I dont think correctly) however the signal becomes distorted, and is nothing like the what it should look like.

Can anyone tell  me how to fix this problem, also I was wondering how can I increase the speed of my input signal? Is there a parameter in the DAQ itself that allows me to control this?

I really need to fix this problem soon, thanks

[Dennis_Knutson]

What's the frequency of the signal you're trying to measure and chart? Are you're a doing single point acquisition in a loop? If that's the case, then how often you do an acquisition is based on software timing which is pretty unreliable unless you're using the timed loop.

The x axis by default, increments by 1. If you want to change that, go to the chart's property page and change the x axis to display relative or absolute time and change the multiplier to reflect the actual acquisition rate. There's also a shipping example called Real-Time Chart that shows how to do it programatically.

[Travis_M.]

Hello Sophie,

There is a big difference between a chart and a graph.  A graph will plot an array of data points, where as a chart will update its plot by adding a single point or an array of points to the plot.  You might want to make a distinction between your need to manipulate the display of your data, and the need to acquire data faster.  If the signal you are plotting is not what you expect in a chart, but looks fine in a graph I suspect the signal you are acquiring is ok, and you just need to change the way you display the data.

Thanks for posting, and let us know if there are any other questions you have on this.

Travis M
Applications Engineer
National Instruments