Hi, first of all you don't need to create signals in loops like you did it in your example. You can use signal generation VIs, which will do all the job for you, from Functions->Analyze->Waveform generation or Functions->Analyze->Signal Processing->Signal Generation palettes.
As for your question you need to use dt LESS then 1/(200*2)=2.5 ms. This is very simple. If frequency is 200 Hz then the period of signal is 5 ms. To generate this signal you need at least 2 points corresponding to its maximum and minimum so the minimal value of dt is 2.5 ms. If you want to generate goodlooking sin wave you need more then 10 points on one period. So if your waveform has N points and corresponds to K periods (N/K > 2) of the wave with frequency F then dt=(K/N)/F. Good luck. Oleg Chutko.
