Shaker control with output from load cell

[rsd111]

Hi

I am using a (analog output) shaker to generate sinusoidal forces at different frequency and of different magnitude. I am also using a load cell (analog input) to sense these forces . The max force generated by shaker decreases as I increase the frequency of vibration. Whereas, the experiment requires the force to be constant when the frequency is changing. I plan to use the max force obtained from the load cell data, as the process parameter, to modify the amplitude of input wave which excites the shaker. I seek help in this regard. I am using PCI6221 and SCC68.

Thanks in advance.

RSD 

[LV_Pro]

When you say the force is less, what do you mean? What is the load cell measuring, is it attached to a mass on the shake table. As you increase the frequency what happens to the table's displacement? Is the amplitude remaining the same, or as I suspect decreasing.To maintain the same amplitude at a higher frequency would require your drive electronics to accelerate the table at a higher rate, which would increase the instaneous force (F=MA). Are you making instantaneous force measurements or are you averaging over time?

[rsd111]

Hi

Thanks for reply.

Less force means the amplitude of force sense by load cell decreases as the frequency of shaker increases. What we do in the experiment is ...we bring the load cell in contact with shaker (so the shaker is not allowed to move) and the shaker is excited with sinusoidal signal.  At present, I increase the gain of amplifier to get higher force and I am measuring instaneous force.

I look forward to your reply.

Thanks again

RSD

[LV_Pro]

Sorry, I have been extremely busy the last couple of days (months?). I still haven't had much time to ponder the problem, but one thought comes to mind, at what frequencies are you running this and what is the load cell, and its supporting electronics, frequency response. You mention that the amplitude decreases as the frequency increases, but that you increase the gain of the driver amplifier. It (the system) is most likely non-linear in its response, so how much you increase the gain will vary. The nonlinearity of the response is one of the reasons there is so much published about control systems, PID controllers, etc.