Demystifying Vibration Monitoring Part 1: Why Vibration Monitoring Matters—And How It Works

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Part 1: Why Vibration Monitoring Matters—And How It Works
Part 2: Vibration Analysis Principles on Rotating Machines
Part 3: Identifying and Interpreting Overall Vibration and Fault Patterns
Part 4: Diagnosing Imbalance, Misalignment, Looseness, and Bearing Wear

Maintenance teams today are stretched thin—managing more assets, with fewer hands. Vibration monitoring helps close that gap, giving early warnings when machines start to wear down.

Vibration is one of the most important, yet often overlooked, indicators of machine health. From the moment a machine is powered on, it starts accumulating wear. Over time, that wear shows up as changes in vibration patterns. By catching those changes early, you can prevent failures, optimize repairs, and extend the life of your assets.

Why is vibration so effective? Because it strikes the perfect balance: it detects issues sooner than thermography or audible noise, but later than technologies that often yield false positives, like ultrasound. In other words, it tells you what you need to know, when you need to know it.

Using simple vibration screening tools, maintenance teams can flag potential problems. More advanced testers can then diagnose the most common faults. And with expert-level analyzers, even complex issues in critical assets can be precisely identified.

What kinds of faults are we talking about? The vast majority of rotating equipment failures come down to four key issues:

• Imbalance
• Misalignment
• Looseness
• Bearing wear

These faults can be detected through characteristic vibration patterns—patterns that sensors and software can now identify automatically.

When tracked over time, vibration becomes more than a fault detector. It becomes a strategic tool. It enables predictive maintenance, where service is performed based on the actual condition of each machine—not a fixed schedule. That means fewer surprises, better planning, and longer-lasting equipment.

In this blog series, we’ll walk you through the essential concepts behind vibration monitoring and analysis—how it works, what it shows, and how it fits into a proactive maintenance strategy.

Understanding Waveforms and Measurement Types

Vibration for a moving object can best be illustrated as a sine wave that repeats over and over along the horizontal axis. In Figure 1, see the mass on a spring that generates a sine wave of vibration as it moves up and down over time. One complete sine wave is a cycle. The time it takes for the cycle to repeat is the frequency or speed of the waveform. 

The vibration waveform also has an amplitude or magnitude that can be measured in the vertical axis, as seen below. There are three ways that the waveform’s amplitude can be reported, as seen in Figure 2. 

1. Peak: the amplitude from the centerline to the top of a peak (or the bottom) 

2. Peak to Peak: the amplitude from the top of a peak to the bottom of a peak (Peak-Peak = 2 X Peak) 

3. RMS: the Root Mean Square of the peaks (RMS = 0.707 X peak) 

The vibration waveform can be expressed using three different methods. 

1. Displacement: The distance an object moves from a reference point. In a rotating machine, it might be measured using a proximity probe. This requires drilling holes into the bearings, so proximity probes are not common. Displacement is best for measuring low frequencies and in units of mils p-p (peak-peak). 
2. Velocity: The distance the object moves over a given time. In a rotating machine, it might be measured using a velocity probe. Velocity probes have moving parts that break, so they are not common. Velocity is best for measuring mid frequencies and in units of in/sec peak (mm/sec). 
3. Mathematically: Velocity = displacement/time (V=d/t) 
4. Acceleration: The rate of change in velocity over time. In a rotating machine, it might be measured using an accelerometer. Accelerometers have no moving parts, are stable over 12-15 years and are very commonly used. Acceleration is best for measuring very high frequencies and in units of g (in/sec2) RMS. 
5. Mathematically: Acceleration = Velocity/time (A=V/t) 

Which method is best? 

For rotating machines, velocity is good for a wide range of frequencies and it is also very good at diagnosing forces of fatigue that cause wear and ultimately failure. The accelerometer is the typical sensor of choice and it is easy to convert the acceleration to velocity (Acceleration = Velocity/time) 

Analogy

When evaluating the damage of a car crash, it isn’t how much distance you have covered, or how fast you are accelerating that causes all of the damage; it is the speed at which you are travelling in your car before you hit the wall. Similarly, velocity as calculated from an accelerometer is the best indication of the damage from the vibration. 

📖 Read Part 2 → Reading the Frequency Spectrum to Find Faults

Author Bio: John Bernet is a Mechanical Application and Product Specialist at Fluke Corporation. Using his 30-plus years of experience in maintenance and operation of nuclear power plants and machinery in commercial plants, John has worked with customers in all industries implementing reliability programs. He is a Certified Category II Vibration Analyst and a Certified Maintenance Reliability Professional (CMRP), with over 20 years of experience diagnosing machine faults.