Why do sample rate affect piezo actuator

[andersne]

Hi,

 

I have a system setup with a piezo actuator and amplifier, a accelerometer and power supply attached to a cantilever beam and NI USB-6251. The aim for the setup is to see how different frequencies generated by the actuator effects the cantilever and what input the accelerometer detect for a given frequency/amplitude. My problem is that it seams clear that the waveform generated is affected by the timing settings. For instance will the actuator produce two different frequencies when I change the sample rate for the system. This is validated both by the accelerometer and notable change in pitch (sound from when the system is running). I've used the Voltage - Continuous Output.vi and simultaneously augured signal from the accelerometer. Why is that so? 

[Jordan Kuehn]

What sample rates and what frequencies are you using?

[andersne]

Hi Jordan,

I've tested the system with a sample rate between 1000-4000 and a frequencies mainly between 100-300Hz, 600Hz at the most. 

[Lipko]

The sampling frequency must be at least twice the signal frequency that you want to measure. But it's better to have higher sampling that.
https://en.wikipedia.org/wiki/Nyquist_frequency

If it was obvious, then sorry.