CHANGE OF AXES

[IAEA]

I am working with a graphics whose axes are Double Amplitude (peak to peak) and Hz and I would like to compare this graphic with another one whose axes are Magnitude in g and Hz. Please, could someone tell me how I must translate this axes (from Double amplitude peak to peak in inch to magnitude in g). Thank you in advance. I would be very grateful if someone answer me as soon as possible.

 

[MikeyP]

I am assuming that this is a spectrum with equally spaced spectral lines, not 1/3 octave bands or similar. You will forgive me if I work in SI units!

1) Multiply the pk-pk values by 0.0254 and divide by 2 to obtain displacement amplitude in metres.

2) Multiply each spectral line by (2*pi*frequency)^2 to get acceleration in metres per square second.

3) Divide by 9.81 to obtain acceleration in g.

M

--
Dr Michael F Platten

 

[sms]

While Dr Mike is correct, I would first ask why? If the first measurement is from a non contact proximity probe which typically has an output in pk to pk displacement, and the second measurement is from an accelerometer on the bearing case, then coverting the displacement signal to g's makes little sense and compareing the two is apples vs oranges. However if both measurements are from a accelerometer, then Dr. Mike's procedure is certainly valid, but I would ask, why didn't you just turn off the integrator when the displacement measurement was made so that you could compare g's with g's.

I would be very interested in more information on what is being measured and how!!

 

[MikeyP]

Erm...

Sms, did you read something in the original post that I missed?

M

--
Dr Michael F Platten

 

[sms]

Mike, perhaps I read too much into it. I have had a lot of trouble with folks in the machinery vibration business taking a pp displacement readings from a proximity probe measuring shaft motion in a fluid film bearing and trying to compare that with casing readings taken with an accelerometer. You can certainly do unit conversions on either measurement, but you are measuring the motion of two entirely different things, so the comparison is not really valid. That is the only point I was trying to make. Sorry if I didn't make it very well....

 

[fard]

hi
We want to construct a balance machine for cement factory fan,
I need some information about the measuring mechanism of balancer, Do they use loadcell or accelerometer?

 

[GregLocock]

There are (broadly) two types of balancing machine. The soft foundation ones use accelerometers, the hard ones use load cells.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.