real time feedback

[pi=3.14159]

Hi,

I modified the 'cont acq&graph voltage-int clk.vi' to acquire a bunch of waveforms (40). I show one of the waveforms real time (in a waveform chart) to the subjects using a for loop that runs for a specified time (for example, 5000 times (sampling rate 1000 Hz * time 5s)). 

Problem I face: The loop timing varies. I.e., sometimes the loop is getting executed fast, say for 4 sec (5000 times). Other times, it is perfect.I use a 'elapsed time.vi' to monitor the time.

My question is:

1. Are the irregularties in the timing related to RAM (1GB) and processor (2.5 GHz) or the VGA capacity of the computer? 

2. Even if I use 'timed loop' the problem persists. It takes a longer time to get executed. As a result I see a sudden brake in the waveform that comes real-time. What could be the problem?

3. Most importantly, how do I plot the graph in real-time continuosly as I receive the input without any time lag.

Your input is highly appreciated.

pi

[Dennis_Knutson]

You are going to have to post your modified VI. I don't understand what you've done with the looping. If you want to acquire 40 waveforms, the loop in the example has to execute 40 times and the number of samples requested should equal the sample rate if you don't want any gaps in the data.

[pi=3.14159]

Hi Dennis,

Thanks for getting back to me. I run the loop using DaqmxRead 'Analog 1D Wfm Nchan 1samp'. I used 'timing source' to monitor the timed loop and pace it according to the sampling rate. And it works fine now!

pi