Hello
I am trying to perform a sine sweep test using OROS 38 DAQ, Modal analysis software and The modal shop shaker 2100E11. The DAQ software allows to specifying the peak to peak voltage from 0 to 10V and I am using natural air cooling for the shaker so the sine peak force is 220 N.
Only accelerometers are available to get the data and no force sensors are available. Is there any way to measure approximate values of force corresponding to the given peak voltage in the DAQ system?
Please help me out with this.
Thank you
Mr. Shaik:
I am not familiar with the specific equipment you use, but if your vibration exciter is a permanent magnet electromagnetic shaker, it might be possible that you can correlate the current input into the shaker’s coil with the output force. If you can set up the power amplifier so that it is in a controlled-current mode, then the current would be proportional to the voltage input to the power amplifier, and the force output of the shaker might be a predictable function of frequency and the current and voltage. I did something like this as reported in an article published in 1989, “Experimental active vibration damping of a plane truss using hybrid actuation,” which is posted on ResearchGate.
You might also find help in a detailed article (perhaps even a series of articles) about shakers written by George Fox Lang, published in the magazine “Sound and Vibration.” I don’t recall when Lang’s articles were published and I can’t find them in a quick look into my files, but I think they came out sometime between 1990 and 2010.
As you are probably aware, the conventional and most reliable method of measuring shaker force output is to position a dynamic force sensor between the shaker sting and the attachment point to the structure.
Yours is a well written question. Good luck finding a satisfactory solution.
William Hallauer
@William L. Hallauer
Thanks for your response. I found Fox Lang article, it is informative.
Sadikbasha Shaik Generally, the sensitivity of the shakers is not constant in the frequency domain. That means that you need different voltages to attain given acceleration/force at different frequencies. Furthermore, the acceleration/force magnitude dependence might not be proportional to the input voltage (i.e. the acceleration vs voltage function at the given frequency is not linear).
Due to these properties, your options include:
Luboš Smolík Thank you for your answer. I have tried mounting an accelerometer on the stinger to obtain base excitation acceleration and giving it as input to the FE model. But accelerometer is giving some random signal for a given sine sweep. I am unable to figure it out where am I going wrong. Could you please suggest something?
Sadikbasha Shaik I would start with attaching the reference accelerometer to the tested object (close to the stinger) rather than to the stinger. Reason: You want to influence shaker properties as little as possible.
If you use a sine sweep, the good idea is to perform the sweep as slowly as possible to minimise the influence of the system delay. Another good idea is to perform so-called order tracking. The order tracking ensures that you record only a synchronous response to the excitation. Then you can estimate:
Some basics of this technique are outlined in the enclosed presentation.
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