Setting sample rate for sinus analog output

[felix_and]

Hello,

I've been trying to do something very simple : using an analog output of the card PCI 6221 to produce a sinus curve of frequency 50 Hz. For this I used a Vi to create a sinus curve and the different DAQmx VIs. But I have difficulties understanding the principle of virtual channel and I think I'm doing a mistake setting the sample rate and samples number : one time for the sinus vi, second time for "DAQmx - Timing". Should I use the same values for both of these VIs ?

On my oscilloscope, with frequency=50Hz and sample rate=1kHz, I get a null signal. Then depending on both values, I get differently rated signals. For example with f=1Hz and sr=10kHz, a sinus of frequency 0,7 Hz.

[RavensFan]

Do you want a sine wave?

A "sinus" wave is a completely different thing.  It is a heartbeat rhythm.  http://en.wikipedia.org/wiki/Sinus_rhythm

[felix_and]

Yes, sorry, I meant sine wave.

[RavensFan]

Try setting the Sample Clock to be Continuous Samples.  Delete the numeric constant from the top.  Right click on the terminal and select Create Constant.  The constant will be a ring constant with a meaningful name rather than a number.

[Dennis_Knutson]

And look at the shipping examples. There is one called Cont Gen Voltage Wfm-Int Clk. It uses a DAQmx Timing function set for Use Waveform to set the timing.

[felix_and]

Yes, thanks for your advice. I used the structure given in the example and now it's working fine. I'm still not sure what I did wrong though.

I would have a second question now (should I create a new topic?):

I put a continuous sine wave on the analog output. As soon as this is running, (or maybe after a short delay) I want to measure a limited amount of samples on my analog input. How can I be sure, it's not going to start measuring before the output is properly set ?

I don't think a trigger would solve the problem since I'm going to vary the output Amplitude.

[RavensFan · Accepted solution]

Make sure the start task for the analog input occurs after the analog output.  By wiring the error wire in to the analog output start task first, then on to the AI start task, you guarantee the AI can't start until after the AO has started.

[felix_and]

Ok, thanks!