Bearing envelope analysisVibration analysis to detect and diagnose faults in bearings and gears

Envelope detection

Envelope detection is a signal processing technique used primarily in vibration analysis to detect and diagnose faults in rotating machinery, such as bearings and gears. It is also used to detect and diagnose faults in roller bearings.

It works by extracting the modulating signal (or envelope) from high-frequency vibration data. This helps to isolate and identify repetitive, impact-like events, such as those caused by a defect in a bearing or gear.

When bearing elements strike a local fault, an impact is generated. These impacts occur at different repeating frequencies, depending on the bearing’s geometry and rotational speed. The repetition rates, or bearing frequencies, are unique to each type of bearing and are calculated using specific mathematical formulas.​⬤

The impacts modulate the signal at specific bearing pass frequencies, including:

• Cage Pass Frequency (CPF)

• Ball Pass Frequency Outer Race (BPFO)

• Ball Pass Frequency Inner Race (BPFI)

• Ball Fault Frequency (BFF)

These frequencies are associated with the unique characteristics of the bearing’s operation.

Envelope Analysis is based on the FFT (Fast Fourier Transform) frequency spectrum of the modulating signal. When the original signal is amplitude-modulated, envelope analysis extracts the modulating signal through amplitude demodulation. The result is the time history of the modulating signal, which can either:

• Be studied directly in the time domain

• Be further analyzed in the frequency domain

This process allows for detailed insight into the behavior of the signal. Dewesoft offers advanced solution for envelope detection. Check our envelope detection SW manual for details.

Applications of Envelope Analysis

Envelope analysis is widely used in industries that rely on rotating machinery, such as:

• Paper manufacturing

• Chemical processing

• Textile production

• Power generation

• Mining

• Steel production

Key uses include:

• Non-intrusive monitoring of roller bearing health

• Identification of cracks in both the inner and outer races of bearings

• Detection of roller defects, wear, and poor lubrication

This technique provides crucial insights for maintaining and diagnosing the condition of rotating equipment.

Bearing Fault Detection With Envelope Detection

Envelope detection is a standard procedure for the early detection of faults on ball bearings.

When a failure of the ball bearing occurs, it will produce ringing with a frequency that corresponds to its natural frequency. This ringing will repeat each time when a damaged part of the ball hits the ring or vice versa. In addition, the inner ring, outer ring, cage, and balls have different typical repeating frequencies depending on the geometry of the bearing and the rotational frequency. 

With DewesoftX data for bearing components are automatically managed by a bearing database. Using envelope detection and the bearing database simplifies pin-pointing critical frequency components related to specific bearing components and enables kinematic cursors to be used. 

Download Bearing Envelope Analysis brochure​​​​​​​.

FFT analysis (Fast Fourier transform)

FFT analyzer module provides all functions for spectral analysis with advanced averaging, selectable resolution (up to 64000 lines), or direct specification of the bandwidth (0.01 Hz). Multiple channels can be displayed in the same FFT visual display for easier comparison. FFT features:

• Multiple cursors and markers: provide easy access to marked frequency values. Free, RMS, Max, Sideband, Harmonic, and Damping markers are available. 

• Bearing cursor: used to identify the bearing frequencies

• Envelope: envelope detection is a procedure for the early detection of faults on ball bearings

• Auto and cross-correlation

• Cepstrum

• Short time FFT

Kinematic markers

Kinematic markers are used to identify the bearing frequencies and bearing faults. DewesoftX software offers a convenient way to add a new bearing go to the Kinematic cursor editor.

Each bearing database includes bearing data (what is the base of the component (cage, rolling element, outer race, and inner race) at 1 Hz and at which frequency has the component a peak in the frequency domain).

Kinematics marker properties:

• Current value: Displays only the current value of the marker and can be interacted with while storing.

• Full history: Stores calculated values in output channels and can be used as input in other modules.

• Snap to data points: If selected, the marker’s position will snap to the FFT bin; otherwise, the marker can be placed at any frequency, with the value interpolated at that exact frequency.

• Find peak in region: If selected, the marker will automatically search for the peak within the selected frequency band centered on the marker’s position.

• Improve peak accuracy: If selected, the peak position and value are interpolated from the FFT data.

• Kinematic cursor: Assign the appropriate marker from the Kinematic Cursor Editor.

• Position source: The position source has two modes—Widget marker and Channel. If the widget marker is selected, the position is defined manually. In Channel mode, the position is defined by the current value of the selected channel.

• Frequency of rotation: Determines the position of the kinematic markers. The frequency must be input manually and can be defined in Hz or RPM.

After setting up, user can see kinematic markers at frequencies defined in the kinematic cursor database. The table will also show which mechanical part each frequency is related to.

Kinematic markers can also be visible on the DewesoftX 3D graph.

Order Tracking Analysis

The order tracking module makes it extremely easy to take time-domain data and transform it into the angular (order) domain. It can extract any number of harmonics (amplitude and phase angles) which can be displayed in Bode, Nyquist, 3D FFT, real-time x-y, and orbit plot. The plane view FFT clearly shows the excitation forces, natural frequencies, and all the resonances to give a clear picture of the dynamic behavior of the machine.

Any input can be used: microphone, accelerometer, and even the output of the torsional vibration module (see below). The patented digital counters technology (Supercounter®) provides very accurate and repeatable measurements. Results are represented on a 3D color spectrogram and 2D graph for selected order and phase extraction over RPM.

Learn more about Order Tracking analysis:

• Order Tracking Analysis solution page

• Order Tracking online PRO training course

• Order Tracking Online Manual​​​​​​​

• Order Tracking Webinar

• Rotating Machinery Analysis Webinar

Main features

Order tracking module features:

• Simple and easy to setup

• Dedicated re-sampling method for sharp order separation

• Measurement in the time domain to keep all benefits

• 2D, 3D waterfall in order or frequency domain

• Amplitude, phase extraction

• Recalculation in post-processing

• Phase synchronous rpm input with 12.5 ns resolution

For more information please visit the Order Tracking PRO training online course.