No, I didn't but I have some reply mail from NI Applications Engineer, details as below.
However, if you have other solution please let me know?
Dear Sir -
You are 100% correct about our NI-DSA driver. It does not support DC
offsets to the Swept Sine signal.
If you would like to add a DC offset to your signal, there are two options:
1) hardware and 2) software.
1) Hardware
You could build a summing amplifier circuit (with inverter) to add a DC
offset to your sine wave. If you not sure what it takes to build a summing
amplifier, check out this website:
http://www.play-hookey.com/analog/experiments/summing_amplifier.html
Remember that this circuit would invert your signal and you would want to
reinvert it before sending it to your actuactor.
2) Software
This is not possible with the NI-DSA driver. But you could use the NI-DAQ
functions with your card and write your own swept sine algorithm. This
would probably take quite a bit of time depending on your familiarity with
LabVIEW, NI-DAQ, and swept sine.
The latest version of our Sound and Vibration toolkit (3.0) does include
functionality for swept sine. I looked at it and it would be pretty
straight forward to add a DC offset to your signal.
Overall:
Using the summing amplifier might be the cheapest and quickest method
(depending on how comfortable you feel with electronic circuits), but if
you want to be able to programmatically control the amount of the offset,
you'll need another voltage source to provide your DC offset signal.
Writing the swept-sine algorithm with NI-DAQ from scratch will take quite
awhile and is not trivial.
The last option is probably the best, but it requires you to purchase the
Sound and Vibration toolkit. Here you would not need another voltage
source and the amount of time the modify the current Swept Sine example
should be fairly small.
Let me know if you have any other questions or how I can help.
Jack Arnold
Applications Engineer
National Instruments
http://www.ni.com/support
