Shiv,
We couldn't really figure out what you really mean with "rate" because you include a half trigger per second and it doesn't tell us much about it, we will need a lot more of detail of what is your program doing and how... and is not enough to look into a VI that we didn't make, hope you understand our point. I would really recommend that you give us call instead of using a text based message it will be a lot easier to understand the overall behaviour of your system.
For the info on how to call us use: www.ni.com/ask
Thanks and we expect to hear from you,
Nestor Sanchez
Applications Engineer
National Instruments
Nestor