signal express execution control by sweep rate

[hasaan]

Sir,I am trying to give harmonic base excitation to a laboratory model of a frame structure with the help of shaker by using Signal Express and recording the response of the model with the help of accelerometers attached on the top of model. The purpose of this exercise is to have frequency response curve (frequency vs. acceleration).I want to sweep the frequency from 2Hz to 8Hz with a fine frequency step (say 0.01 Hz) near the first eigen frequency (e.g 3.6 Hz). But the problem is that I could not control the sweep rate of the frequency. I want to excite the shaker at each frequency step for 30sec to avoid beat phenomenon and till the next frequency comes in action. At the moment, the program is working but without any user controlled sweep rate of frequency in real time and thus I get different frequency response curve each time. Please guide me how to control the sweep rate by using Signal express. The program consist of the following main steps within the loop of sweep of the frequency 

1. Create signal; sine wave
2. Generate signal; NI-DAQmx  Generate
3. Acquire signal; NI-DAQmx  Generate
4. Filter; to get smooth function
5. Tone extraction; to get peak value  from time domain against each frequency
6. Save to ascii; freq vs detected amplitude

 Thanks in advance,Basit KhalidCentre of Mechanics and Structural Dynamics (TUWIEN)