Predictive Maintenance, Machine Condition Monitoring, Vibration Analysis - What are these terms?
Vibrations and Vibration Diagnostics
Let’s explain briefly what the vibrations, which we are focusing on, really are. Electric motors vibrate when running and you can hear a sound (a noise) because noise is in fact vibration. We guess there is no need to explain that when you speak your vocal cords generate vibrations which are transmitted through the air to other person’s ear. You cannot see these vibrations, but you can hear them. Imagine the bass speaker while playing some music. Can you see the movement of the speaker membrane? Yes, you can. But can you see the movement of the motor while it is running? Not really. To 'see' a motor’s vibrations we’ve got some excellent helpers today: an acceleration sensor and vibration meter or analyzer.
Talking about the speaker again, can you separate each noise which comes from the speaker while playing some music? You can easily separate basses (low frequencies) from trebles (high frequencies) with an equalizer. Why we are still talking about speakers? Because it is very similar to the vibrations on the machine. On the machine we also want to separate those 'bass and treble' noises but here we are talking about separating machine faults, such as overall machine condition related to shaft speed (low frequency) and bearing / gearbox faults (higher frequency).
To separate these faults we use the vibration meters and analyzers mentioned above. While performing Vibration Diagnostics we want to distinguish two important things which we get from the signal: overall machine condition and bearing condition, (as each of them is diagnosed from different parts of the vibration signal.)
Vibration Diagnostics is more sophisticated of course and later on you will find out that you need to separate more vibration sources which are generated by a running machine (for example loose foundation bolts, unbalance, misalignment, fan blade faults, gear mesh faults and many more.) But for now let's just talk about those two basic things for easier explanation.
Machine Condition Monitoring
There are more methods for evaluating a machine's condition and its faults. Besides Vibration Diagnostics you may have heard about Ultrasonic detection, Thermography, Non-destructive Testing etc. and all these methods are part of Machine Condition Monitoring. Each method has its pros and cons; it is up to your maintenance program which methods you select (or combine them) and which methods are the best for your particular machines. However, during the last few decades it has been found and proven that Vibration Diagnostics is the most efficient and reliable method for most rotating machinery.