Difference between Vibration Acceleration and Enveloped Acceleration
QUESTION
Vibration Pen is used to1) measure vibration caused by rotational and structure problems like
imbalance, misalignment,looseness etc;( measured in mm/sec;RMS ) called Overall Vibration;
and 2) measuring vibration in higher frequencies caused by rolling element bearing or gear
mesh problems ( measured in gE ) called Enveloped Acceleration.
Are Overall Vibration and Vibration acceleration same? In Enveloped Acceleration g and E (gE )
stands for what.
Moreover what does Vibration Displacement ( Units --mils ) measure.
ANSWER
Vibration acceleration and enveloped acceleration are not same things.
Normal acceleration (G’s) is like other vibration parameters like velocity , displacement
measured in certain frequency range for detecting various faults.
Enveloped acceleration (gE) is obtained by passing the signal through high pass filter,
enveloping , low pass filtering, FFT , and shifting the resultant spectrum to zero frequency
starting. It is the effect of a certain vibration in a high frequency range. Defects in incipient
stages normally produce high frequency signals. enveloped acceleration is better suited to such
problems like bearing initial stages of failure, gear problems etc. Absolute value of enveloped
acceleration is not much meaningful .
Vibration displacement in mils (thousandth part of an inch) is the peak to peak displacement of a
vibrating component.
Overall vibration can be measured as displacement, velocity or acceleration as required.
In gE term, g stands for gravitational acceleration to measure acceleration in unit independent
terms, E stands for enveloped.