Signal phase shift problem

[r_ramirez]

Greetings

I need to analyze three sinusoidal signals 120 degrees out of phase by nature including my version of LabVIEW 7.1 and the acquisition card I used is the Measurement Computing USB 1208FS. In principle the acquisition and display them individually does not represent any kind of inconvenience, the problem arises when I try to observe the three signals in the same waveform graph. At this point to run the test continuously (Continuously RUN) the signals lose their phase shift and this becomes variable along the process of signal acquisition occasionally taking its original phase shift (in Figure 2 shows how to vary the phase angle between the signals), just watch the same channel form using 3 distinct stages and the signal (in theory the same) is outdated fig 4. How can this problem be corrected? There is some appreciable time lag between data collection in the different channels that would alter the correct acquisition of the signals. You can correct varying the sampling frequency (rate) and the count?

 I need the visualization and processing of three-phase signals in 'real time', because the amplitudes of these vary over time, which is why I run the program in RUN Continuously, otherwise the data acquisition would not be made continuously.

[Pablop]

Can you post any vi's and or data? It's hard to visualize what you are talking about.

Running continuously is tricky, because programs usually run something like:

1) Aquire Data

2) Analyse Data

3) Display Data

4) Repeat

With the correct use of memory buffers, this can seem continuous, but it would depend on your hardware and software. Generally speaking, correctly configured data aquisition can haev simultaneous channels. What hardware are you using?

Running the LabVIEW program continuously is nto the method you want to use. You should use a While Loop, with a stop button.

[r_ramirez]

hello and thank you for answering im acquiring data through potential transformers, the acquisition card is Measurement Computing USB1208FS attached the .vi used in development distribution, an outdated image of the signals (for the same channel), how can i continuously acquire a signal with a while loop without applying Continuously run? thanks again

[RavensFan]

Put a big while loop around all of your code and wire a Stop button to the while loop stop terminal.

[Cory_K]

I didnt realize he started a 3rd thread.

This thread is also taking place here

[Dennis_Knutson]

I suspect that you are really, really using those Measurement Computing express VI in the wrong way. You should confirm with them but try using only one for all channels instead of three separate ones. If they work like I suspect, all of the acquisitions will take place at the same time.

[Pablop]

RE: Using a while loop, just check the LabVIEW examples, it's pretty basic.

Dennis is right. You won't maintain synchronized signal with 3 separate aquisitions. The fact that you have soemthing that appears synchronized is simply a reasonably fast computer dutifully performing.

You have to aquire the signals simultaneously.  I notice that there is a chapter on synchronizing in the user manual for the Measurement Computing USB1208FS, I think yo need to study it.