Sensor Types vs Phase Relationship 3

[RayGary]

I am using an accelerometer to take vibration readings of a rotor that spins in the 10 to 60 hz frequency range. When determining the phase relationship of the strobe to the heavy spot on the rotor, does the type of sensor affect the phase information collected?
Since there is a phase difference between displacement,velocity,and acceleration curves, does a measurement of displacement, velocity, or acceleration require an adjustment constant in the calculation to relate the heavy spot to the strobe depending of the type of sensor used to collect the data? ie
Does the peak measurement of the accelerometer occur at the heavy spot of the rotor or 90 degrees prior?

 

[GregLocock]

"Does the peak measurement of the accelerometer occur at the heavy spot of the rotor or 90 degrees prior?"

I'd be hesitant to claim that there is a fixed relationship, but if there was then I'd expect it to be at either 0 or 180 depending on polarity etc.

"Since there is a phase difference between displacement,velocity,and acceleration curves, does a measurement of displacement, velocity, or acceleration require an adjustment constant in the calculation to relate the heavy spot to the strobe depending of the type of sensor used to collect the data?"

absolutely, there is 90 degrees difference between acc and vel, and vel and disp.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[MachineryWatch]

Greg is absolutely correct about the phase relationships of accel,, vel., and displacement.

Phase lag is dependent on the entire instrumentation system not just the sensor used. In the days when I used analog instrumentation and strobe lights for balancing, if you had several identical instruments you had to establish the lag for each instrument if you were going to use rotor sensitivity information to do a "One Run" balance, you had to factor in the lag of the instrument you were using when attempting the procedure. For example we had access to several IRD 350 analyzers. While all of them were kept in good repair and calibrated (these were for Navy nuclear work) they had differing phase lags.

http://www.machinerywatch.com

 

[Tmoose]

Where the rpm is on the system's response curve can make ~ 180 degree change in phase.

http://www.nanoscience.com/products/QControl/i/res_curve.gif

Those old green Stewart Warner balancers used mechanical resonance to amplify the motion and create a larger unbalance signal.

http://s3.racingjunk.com/ui/2/08/24458082-630-Stewart-Warner-Model-2380-Balancing-Mac.jpg

The process was to rev the part above resonance and note the phase, then slow the part down and note the amplitude as it passed thru resonance. The "picture" (phase) would shift 90 as the rpm approached resonance, and another 90 as the part slowed way down.