signal express - Sweep through frequency of a generated signal

[kc9383]

Hi-

I am trying to use my APS Dynamics Shaker to generate a linear sine sweep (through a frequency range) using signal express. Because I need to "Create Signal" in order to have an input for the Generate Signal, my frequency seems to be set (I need to set it in the create signal block). Then when I try to sweep through frequencies (say 300 hz to 10 hz with 5000 points) my shaker makes random tones that do not linearly go from 300 to 10 hz. I also have some "beating" of the signal. I'm not sure if this is caused by the fact that my created signal has a "set" frequency...Any help would be appreciated.

I also would like to do a "stepped sine sweep" that dwells at certain frequencies if that is possible.

thanks!

kaitlyn

[Matt_K]

Hi Kaitlyn,

What specific generation block are you sending the output of your Create Signal block to?  Also, what is the model of your signal generator?

- Matt

[kc9383]

Hi Matt-

I am using the DAQmx Generate - Analog Output - Voltage. My DAQpad is model: NI USB 6251 and I'm using the connector block BNC 2110.

Thanks!

Kaitlyn

[sensei]

Hello,

The nonlinear sweep you're seeing is probably due to the device being reconfigured at a different rate each iteration of the sweep.  In SignalExpress, you cannot reconfigure the rate of your generation without reconfiguring the device.  With that said, I think you can do the following to accomplish the sweep from 300 Hz to 10 Hz.  Here's what I did as an experiment... you'll have to change the parameters as needed for your 300 Hz to 10 Hz case.

1.  In Create Signal, I set the Sample rate to 10,000 S/s, and the block size to 10,0000.

2.  In DAQmx Generate, I set the Generation Mode to Continuous Samples, I unchecked the box for "Inherit Waveform Timing" (it's the checkbox next to "Generation Mode"), I set the Samples to Write to 10,000, and I set the Rate to 100k.  Go to the Advanced Timing tab and change the Regeneration Mode to Do Not Allow Regeneration.

3.  Drop a Sweep step and put the Create Signal and DAQmx Generate into the Sweep.  In the Sweep step, configure a sweep of the Create Signal's Frequency parameter.  I configured mine to go from 1 Hz to 10 Hz with 10 points.

So what we're doing is we're setting up the device to update at 100,000 samples/sec.  That isn't going to change.  What will change is the frequency of the signal that Create Signal is generating.

Regards,

Sensei Lee