The Basics of Vibration Analysis

Reducing unnecessary wear on rotational equipment

Published: Thursday, November 18, 2021 - 12:02

There are various nondestructive testing (NDT) methods we can employ to evaluate the condition of different machine components, without the need to stop and disassemble the equipment. Vibration analysis is a prominent NDT tool used across many industries.

In this article, we will take a good look at the intricacies of the vibration analysis process, parameters, tools, and use cases.

Why vibration?

Vibrations occur in all moving machinery while in operation. Every material has a characteristic pattern of vibration under specific conditions. Measuring, recording, and studying the changes in these vibration characteristics can help us understand the changes in the test material itself.

What is vibration analysis?

Vibration analysis is a process that uses vibration signals to identify anomalies in vibration patterns. A change in the vibration pattern indicates a change in the physical properties of the test object.

In equipment maintenance, vibration analysis helps us track and evaluate the condition of our equipment.

When an anomalous pattern is observed, we can conduct root cause analysis to identify the reason for the change. Once we know that, if it is deemed necessary, we can schedule appropriate corrective maintenance action.

Where and when is it used?

Vibration analysis is suited to test components that undergo rotary motion; that is, components that experience torsional forces. It is used to test or track the conditions of:
• Bearings, gears, shafts, rotors
• Motors, fans, drivetrains, gearboxes
• Pumps, piston engines, compressors, and other reciprocate machines

Don’t take this as a complete list. Vibration analysis has many more niche applications and isn’t limited to rotating machinery or machinery vibration alone.

For instance, vibration data can be gathered to measure the changes and fluctuations in electrical and magnetic fields, as well as to monitor the structural integrity of bridges, pipes, and other infrastructure.

Inspecting gearboxes

Broken gears are a common occurrence in gearboxes. Broken gears will cause a lot of damage before you can see that something is wrong. Vibration analysis helps identify broken gear teeth early, without the need to disassemble anything. This way, we can create a work order and fix the problem before it causes a catastrophic failure.

Catching bearing defects

Bearing faults cause excessive vibration in machines with rotating parts. Monitoring bearing conditions using vibration analysis helps to identify bearing failures and point to appropriate corrective action.

Vibration analysis shines the light on the exact bearing defect, which can include:
• Reverse loading
• False brinelling
• Overheating
• Fatigue
• Corrosion
• Fitting problems
• Misalignment
• Imbalance

Condition monitoring for pipelines

Oil pipelines are another good example of concealed operations. A common problem here is corrosion that can lead to leaks and fire hazards. As you can probably guess, by using oscillation and vibration frequencies data, it’s possible to analyze and measure the corrosion inside pipelines with the help of vibration analysis.

Corroded pipes that carry fluid with a fixed rate of flow have different vibration characteristics compared to a healthy pipeline with the same rate of flow.

Vibration analysis process

The standard steps we need to take to perform vibration analysis are:
Establish a baseline. Conduct vibration analysis on a machine that is operating with ideal characteristics. The vibration levels are recorded to serve as the baseline for this (type of) machine.
Develop a routine. Analysis has to be done at regular intervals. Choose an appropriate interval to conduct vibration analysis. The interval chosen should reflect the machine characteristics and operating conditions. (If you install sensors for streaming real-time vibration data, you can skip this step.)
Standardize the process. The tools and techniques used to perform vibration analysis must be standardized. Using the same equipment with consistent SOPs should give comparable results.
Ensure record keeping. The results of all periodic analyses have to be stored. This helps to keep a record of the historical data of the machine. This is essential for continued analysis. (If you have an online monitoring system, it will automatically store past vibration data.)
Perform vibration analysis. The result of each vibration analysis inspection is compared with baseline data to catch anomalies and defects, and perform required maintenance work.

Vibration measurement parameters

Every vibration, represented as a waveform, has a frequency, amplitude, and period:
Frequency: This is the number of vibrations occurring every second. Frequency is measured in hertz (Hz).
Amplitude: This is the maximum displacement of the wave from the equilibrium position. An RMS value is the commonly used value for amplitude.
Period: The time between two crests or troughs in a waveform is the period. It’s measured in seconds or other suitable units of time. The period is the inverse of frequency.

In vibration analysis, the amplitude is measured and recorded in terms of three physical parameters. They are:
Displacement: This represents the distance between the at-rest position of the component and the maximum position to which it deviates. It measures how much the component moves. The units of measurement are millimeters (mm), micrometers (μm), or other appropriate displacement units.
Velocity: This represents the displacement per unit of time. It’s a measure of how fast the component is vibrating. The units are typically millimeters per second (mm/s) or micrometers per second (μm/s).
Acceleration: This represents the rate of change of velocity. It’s the highest when the movement of the component reverses in direction. It’s measured in millimeters per second squared (mm/s2) or micrometers per second squared (μm/s2).

Vibration can be divided into three categories based on human perceptions: something we can see, sense by touching, or hear. Source: IMV Corp.

Do you need special vibration analysis equipment to perform vibration analysis?

The answer is yes. We can’t measure vibration with a screwdriver. Let’s briefly discuss the important vibration analysis equipment you should be aware of.

Vibration sensors

Different vibration parameters are measured with different types of sensors. Hence, we can differentiate between displacement sensors, velocity sensors, and accelerometers.

The most commonly used types are accelerometer sensors such as piezoelectric accelerometers, microelectromechanical sensors (MEMS), proximity probes, laser Doppler vibrometers, and similar.

Different types of vibration sensors

Which sensor should you buy? Well, that depends on your application. Purchase price aside, you must consider features like:
• Vibration amplitude
• Sensitivity
• Bandwidth
• Noise
• Sensor mounting options
• Number of axes it can cover at once
• Sampling frequency

We won’t go into too many details here, but for everyone who wants to learn more about these features, read this great guide on Choosing the Right Sensor for Vibration Analysis.

Vibration analysis software

Here’s a short list of different vibration analysis software I came across while writing this article:
• EI Analytic
• Vibinspect from ReVibe Energy
• Dplot
• Control Software from Vibration Research
• ProAnalyst from Xcitex
• Lab Software from enDAQ
• FEM tools

Some of those solutions are used specifically for vibration analysis, while others are part of larger software packages that have many other applications. Perform your due diligence before making any purchases.

Online vibration monitoring systems

An online vibration monitoring system presents a setup where:
• You have installed vibration sensors on your critical equipment.
• Those sensors are continuously sending real-time data into the cloud.
• Your selected vibration software reads and analyzes incoming vibration data and reports warnings and recommendations.

Based on the analysis, you can schedule appropriate maintenance actions.

Portable vibration monitoring equipment

Installing sensors isn’t the only way to get vibration data. There are plenty of portable vibration equipment as well as maintenance engineers and technicians you can use to perform vibration measurements.

Portable vibration monitoring equipment

Handheld vibration meters are useful for organizations that run condition-based maintenance. They can use a computerized maintenance management system (CMMS) to schedule regular vibration measurements for different components and machines.

The ‘analyzer’ part of vibration analysis

Data from vibration sensors and equipment are collected and recorded by data-collecting software tools. The software records the data in one of two formats (or in both):
1. Time waveform: Time waveform is the raw data from the sensor. The two variables constituting the waveform are amplitude and time. Nowadays, its use is increasingly rare.
2. Fast Fourier transform (FFT): A Fast Fourier transform wave is generated from the time waveform. The amplitude is represented as frequency plotted against time. Computer technology has made FFT a much better tool to analyze machine health.

The vibration data from the sensor can be analyzed by trained vibration analysts or reliability engineers. Computer algorithms and analysis tools can also be employed to detect anomalies and to verify the health of the tested components.

Using FTT spectrum analysis for vibration analysis. Source: IMV Corp.

Time waveform analysis can show whether there are defects in the test subject. However, it can’t determine the cause for the anomaly. With Fast Fourier transform, on the other hand, we are able to pinpoint the root cause of the defect.

For example, imagine you’re performing a real-world vibration analysis on a system with a motor, a belt, and a drive shaft. Vibration data are sensed by appropriate sensors and recorded via analyzer software. The data are captured as a simple time waveform. You can identify that there is an anomaly from the baseline, but nothing more. Time waveform can’t determine whether the defect is with the motor, belt, or drive shaft.

This is where FFT comes into play. Because FFT gives discrete waveforms for each of the different components (motor/belt/driveshaft), you can pinpoint the exact location of the defect, ultimately leading to a much shorter downtime. Using algorithms to conduct the analysis has made FFT more accurate and precise.

Training, certification, and accreditation

Vibration analysis is conducted by reliability engineers and trained vibration analysts. There are institutes that train and certify technicians to perform vibration analysis:
• American Society for Nondestructive Testing (ASNT) is a pioneer in accrediting reliability engineers for nondestructive testing. Vibration analysis is a part of the courses and certifications from ASNT.
• The Vibration Institute is dedicated to training and certifying vibration analysts. The certification ranges from Category I to Category IV vibration analysts. The Vibration Institute is recognized by the American National Standards Institute (ANSI).
• Mobius Institute provides training in condition monitoring, maintenance, and asset reliability engineering. It offers training and certifications for vibration analysis. The certifications from the institute are accredited by the International Organization for Standardization (ISO).

Let’s also note that the U.S. Dept. of Labor also recognizes nondestructive testing specialists. This includes those specializing in vibration analysis. Beyond that, every country has its own certification and accreditation systems to recognize qualified reliability engineers.

Vibration analysis and equipment maintenance

Here are short explanations on how vibration measurements can help in both proactive and reactive maintenance scenarios.

Using vibration analysis for predictive maintenance

Knowing when and why a component or machine will fail is the key to successful predictive maintenance programs. Vibration analysis provides useful data points you will feed to your predictive data model to improve its accuracy in forecasting equipment failures.

To get the most out of vibration analysis and predictive analytics, you should combine them with modern CMMS software like Limble. Limble can communicate with your vibration sensor and, based on how you set it up, automatically trigger emergency work orders.

A triggered work order in Limble CMMS based on vibration sensor data

Using vibration analysis for breakdowns and corrective maintenance

Vibration analysis can also be helpful in a reactive scenario. You can perform vibration analysis as part of your breakdown maintenance process to help identify the root cause of the failure. This will help you to:
1. Take the appropriate corrective action to address the fault
2. Prevent a similar failure from occurring in the future

If you are using Limble CMMS, technicians can leave comments while closing a work order, such as notes about discovered failure causes, vibration testing data, equipment condition, and downtime.
These data can be used by:
• Reliability engineers when performing failure analysis
• Maintenance managers for evaluating maintenance costs
• Technicians to speed up future troubleshooting and repair processes on this type of equipment

Advantages and limitations of vibration analysis

Like any other maintenance tool or technique, vibration analysis comes with specific advantages and limitations. Knowing these will help you identify viable use cases for vibration analysis on your plant floor.

Advantages of vibration analysis:
• It can be used to monitor hard-to-access components without planned shutdowns.
• With the right setup, it can be used remotely.
• It can provide real-time insight into the condition of your critical assets.
• There are many established SOPs, methodologies, and software you can use to simplify the vibration analysis process.
• There are many commercially available sensors developed for tracking specific operational conditions.

Limitations of vibration analysis:
• Expertise, training, and certifications are needed to correctly perform vibration analysis.
• It can’t be used to track fast-moving defects (i.e., defects that propagate through the machine in a short amount of time).
• It requires some up-front investment into vibration equipment and software tools.
• It can be complicated to conduct fault localization.

When all is said and done, vibration monitoring is a powerful ally for any organization that is running predictive maintenance or condition-based maintenance. However, any implementation of sensors and tools should be preceded by a cost-benefit analysis.

The early bird gets the worm

Catching equipment deterioration as early as possible can save your organization money in the long run, especially if your business processes rely on expensive physical assets.

With more breathing room, your maintenance team has ample time to order replacement parts, allocate the necessary tools, and schedule maintenance work in coordination with production and other departments.

Thanks to CMMS, vibration analysis, and other condition-monitoring tools, organizing maintenance work has never been this easy.

First published Oct. 27, 2021, on the Limble CMMS blog.

About The Author

Bryan Christiansen

Bryan Christiansen is the founder and CEO of Limble CMMS. Limble is a modern, easy to use mobile CMMS software that takes the stress and chaos out of maintenance by helping managers organize, automate, and streamline their maintenance operations.