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MathCAD has a Caps "FFT" and a small "fft" function. THe help files say that the difference between the two is because of the difference in the way you define the function with either a +ve exponent or a -ve exponent. Ive not been able to understand this, but I heard from...

Thanks a lot guys..

Hi Greg Thanks for the post. Ive read those application notes atleast 10 times each. Let me state my question clearer. Say that I have the time domain data for every second as I stated before. I convert this to the freq domain with an FFT function. We now have the signature of the machine at...

I neeed to know the mathematics behind the generation of waterfall plots. I have the time domain data (say some 2^n points gathered every 1 second thru the running speed range of the machine) and would like to convert that to the frequency domain and construct the waterfall plot from it. Any...

Electricpete..The approximation has worked out quite well for me in most cases. The fact that Zeta gets squared adds to this.

Let me go ahead and state the obvious. From the decaying time graph one can get the amplitudes of the peaks. the logarithmic decrement is given by logdec delta=ln(Xn/Xn-1) ln=natural log Xn,Xn-1= amplitudes of 2 successive peaks. The llogdec and the damping ratio are related by logdec =...

http://www.engnetbase.com/default.asp search for modal participation factor.

Greglocock, I was of the opinion that if the microdot cable is bad, then the red "Fault" light in the Signal conditioner unit turns on. I have only used PCB accelerometers; is this true in other units also? Rasmumm are you doing any sort of processing (say integration) on the signal? I...

Vanstoja Does your email address have spaces bewteen 'johnvan' and 10 and '@'?

vanstoja , can I hav a copy of that 22 articles u sent to micjk reg. damping? Im presently working at the Texas A&M turbo Lab on Internal damping and would like to know if you have any papers on damping that I am missing..if u have time u can first mail me the list of papers and we can go from...

http://engineering.rowan.edu/~polikar/WAVELETS/WTtutorial.html Has some material on STFT..I cant think of any application to RD.

Im sorry I dont know the answer, but why would anyone want the units as sones when db is easier(I think..am I wrong??) to comprehend?

Yes for rigid rotors and No for flex. When we balance a rotor we choose a speed lower than the critical so that we get an accurate phase(at speeds close to the critical the phsae changes rapidly with speed). By doing so we achieve the objective of making the rotor pass the critical without a...

Electripete I still dont get you. When we have not at all gathered a DC component(i.e, the time domain data is oscillating about a zero value; say the readings are from an accelerometer) then why would we have to remove it? And another question that i have is how can we do a conversion from acc...

Electripete IF you configure the setting of the spectrum analyzer to AC coupling, do you think it will still gather the DC offset?

Accelerometers normally have an internal resonant frequency(usually of the order of 16 Khz). Check the specs of your accmeter fr the same.

Hello One rule of thumb to get velocities from accelerometer readings is to divide it by the frequency(displacements are obtained by dividing the square of the frequency). So if you have a set of acceleration data over a range of frequencies, divide the values at each and every freq by the...