The Envelope Analysis method allows for monitoring the condition of a bearing using the measured vibration signal. A damaged bearing is a strong generator of impact pulses. These pulses are very short and damped but carry crucial information about the stage of damage in the rolling bearing. Since direct frequency analysis cannot process these short pulses, Envelope Analysis must be utilized, which creates an envelope curve around the time-domain measured signal.
First, the measured signal is filtered with a high-pass filter (band-pass filter) to remove frequencies related to bearing rotations and other interfering frequencies. After filtering, we obtain a signal containing only high frequencies that carry information about the impact pulses.
In the next step, the signal is rectified and further filtered with a low-pass filter. This process removes the carrier signal of the rotating bearing, resulting in the envelope of the original time-domain signal. The resulting envelope signal is further analyzed using frequency spectrum applications like FFT (Fast Fourier Transform).