analog out sine waveform discontinuity

[Rafa_sony]

while usign the generate continuos sinewave.vi if i change update rate, #of points or cycles i get a very brief DC voltage on the output. What can i do to eliminate the DC voltage.
All of this is becouse i am trying to make a sweep generator wit the 4451 analog out. any tips would help. thanks

[Gerald Albertini]

I'm not sure I know which version of the generate continuous sinewave.vi you're using...
The one I could find on my machine doesn't allow to change the sine wave parameters on the fly.

Anyway, there are mutliple ways to create a sweep generator using a 4451...some are better than others.

For instance, you could decide to use a sine period in a lookup table and change the sampling frequency (actually the update rate) so that you can change the actual frequency of the generated sine wave.
This may not be a good idea while using a NI-4451 since this board is using sigma-delta D/A converters and changing the update rate "on the fly" should not be allowed

Another solution is based on continuous generation (at a fixed update rate) and the creat
ion of buffers that contain the appropriate waveform.
The attached example shows a very basic example that shows how to do this.
As you will notice,I set the "Allow regeneration" parameter to "False"
I also select the buffer size parameter so that it contains one period of the lowest frequency to generate (as the frequency increases, it will contain more and more cycles)
Depending on the device you're trying to test, you may also have to take some extra-care with the sine wave generation (more specifically, make sure the frequency transitions happen at a zero-crossing)

This is a very basic example - I hope it will help you get started.

Can you tell me more about the kind of application you're developping and the measurements you're looking for ?

Gerald