PXI analog output card synchronisation

[idrisi]

can anyone help me!

i am trying to generate 3 analog signals two from PXI 6711 and one from a PXI 6733 (see attatched VI).

i am having problems synchronising the two cards so that all three signals have the same phase.

all three signals have the same frequency and the same resulting sample clock rates (caluclated by the wave frorm buffer generation VI)

the daqmx timing VI fro both cards are triggered using one waveform.

i think a possible problem is that both boards have different FIFO buffer sizes,so one cards buffer holds more cyles than the other. even thogh both signals are initiated by at the

same time, one buffer is emptied before the other resulting in a shifing phase. (however the number of cycles held in the PXI6711 is twice that of the PXI6733 which should not really cause this shifting effect).

please help!

thanks in advance

[EmmaR]

Hi idrisi,

The reason you are currently getting that shifting effect is that you are using software timing to start waveform generation.

The problem with this is that you cannot guarantee the sine and square wave are beginning to generate their waveforms at the same instance.

This is the cause of the phase shift you are seeing. Although the waveforms have the same sample clock rate and are being generated at the same time one of the waveforms is starting generation later than the other.

What you need to implement is hardware timing to ensure that both waveforms simultaneously start generation.

I have attached an example piece of code which demonstrates how this can be done by using a digital trigger to ensure both your square wave and sine wave begin generation at the same time.

I hope this helps you,

Emma Rogulska

NIUK & Ireland

[idrisi]

thanks for your help, i have already solved this problem but will check your solution out also!

thanks again.