Machine Health Analysis
Using cursors in VibInspect
Using cursors for machine analysis
Cursors are one of the more important and versatile tools to analyze vibration measurements from different types of machines to detect potential failure modes ahead of time. In VibInspect, we have included functionalities to analyze potential failure modes for bearings, gearboxes, belts & pulleys, electric motors, and pumps/fans. By simply importing the measurements recorded with the ReLog you can within seconds analyze the data and detect potential failure modes.
This feature has been developed together with our customers, to ensure that they can record vibrations on their most critical machines and then proceed to analyze the condition of their bearings. This provides them with crucial information on how to act to avoid unplanned breakdowns.
Understanding different machines before they break down
Cursors can be used to highlight important features in the spectrums, including fault frequency indication for:
- Belts & Pulleys
- Electric motors
Performing a bearing analysis
As bearings age, they are inevitably subjected to wear and tear. This often manifests itself as damage to the contact surfaces of the bearing balls and races – for example pitting, gouging and other unevenness.
When a ball rolls over a damaged point in the inner or outer raceway, a small impact occurs, which gives rise to vibrations. Such impacts will happen as often as a ball passes the defect. We can use this when analysing vibrations from bearings, by looking for spectral peaks matching the ball-pass frequencies, commonly abbreviated BPFI and BPFO (ball pass frequency inner/outer race).
Vibinspect calculates the BPFO and BPFI frequencies for you and shows where they are in the spectral plot. You simply choose your bearing make and model, enter your rotational speed, and Vibinspect does the rest.
The same procedure can be applied to look for damage to the balls themselves. In this case, the important frequency to look for in the spectrum is called 2xBSF, which means two times the ball spin frequency. Why is there a factor 2 before the ball spin frequency, you may ask? Because if there is a defect on a contact surface of a ball, it will cause two impacts for every full ball revolution – one against the inner race, and one against the outer.
Lastly, for detecting damage to the cage, we look for frequency content at the so-called FTF, or fundamental train frequency, which is the rotation frequency of the bearing cage. Vibinspect calculates 2xBSF and FTF for you, just like BPFI and BPFO.
How to distinguish noise from peaks
This is quite common. The background noise is sometimes so high that race or ball damage can’t be detected in a normal spectrum until it’s too late. Fortunately, there are techniques that make fault-indicating peaks be more discernible. Envelope analysis can be used for this.
When a bearing defect causes an impact, it makes the bearing vibrate with the bearing’s own resonance frequencies, usually in the range 2 kHz – 6 kHz (sometimes the bearing manufacturer provides this information). So, every time an impact occurs (which happens with frequency BPFI, BPFO, 2xBSF or FTF), the bearing vibrates at 2 kHz – 6 kHz. In the signal processing language, the bearing’s natural frequencies are said to be modulated with BPFI/BPFO/2xBSF/FTF. Envelope analysis utilises this by performing an operation called demodulation. This technique makes peaks arising from bearing impacts much clearer, so that incipient faults can be detected earlier than in a normal spectrum.
Envelope analysis is easy to perform in Vibinspect – just check the “Envelope spectrum” checkbox when doing an FFT, select which frequencies to focus on (in this case, the bearing’s natural frequencies), and you will get an enveloped spectrum – hopefully without indications of faults in your bearing!
Let us show you how its done
Let us show you how it's done
An instructional video on how to detect bearing failure using VibInspect and the ReLog
- Importing the data to VibInspect
- Choosing the right bearing
- Adjusting the peak search bandwith if necessary
- Analyse characteristic fault frequencies for the chosen bearing
- Comparing vibration measurements from different occasions
- Detecting potential faults to the bearings and the machine
ReLog vibration datalogger & VibInspect analysis software
- Create and take ownership of your own maintenance plan and vibration measurements
- Perform simple vibration measurements without compromising on data quality
- Implement predictive maintenance measurements as part of your everyday work to build knowledge and data over time
- Make decisions based on measurements and data instead of gut feeling