Vibration Analysis: What is it? [4 Measurement Techniques]

What is vibration analysis?

Vibration Analysis (VA) collects vibrations detected from equipment and measures them against known failure vibrations to identify potential failure points.

VA can help maintenance professionals proactively address performance issues before machines break on the job.

Why Vibration Analysis Matters

Vibration analysis’ ability to predict potential failures makes it a useful tool to plan maintenance, boost asset performance, and prevent unscheduled downtime. It is one of the tools in the predictive maintenance (PdM) tool kit.

Vibration analysis helps conduct condition monitoring to identify potential failures, which ultimately saves money by:

1. Reducing unplanned downtime and scheduling work that fits an organization’s plans
2. Saving money by boosting product quality through equipment operating at designed performance levels
3. Eliminating wasted production costs while unplanned repairs are made
4. Delivering products on time with reliable equipment

Vibration Measurement Techniques

Implementing vibration analysis is only the first step in actually using and benefiting from this technique. The complete processes of vibration measurement techniques is described as follows:

Calculate the Vibration Spectrum

For most systems, you can measure various points on its vibration spectrum. Using this data, you can produce a model that illustrates expected vibration behavior.

Establish a Baseline

In order to take full advantage of your vibration data in your predictive maintenance program, you must establish baseline data to inform your condition monitoring. There are normal levels of vibration and acceptable variations that do not indicate failure. Baseline data will set parameters around what performance is acceptables in order to make abnormalities clear.

Generate Signal Models

Vibration data must be translated from the format in which it is collected (typically frequency, amplitude, etc.). The data needs to be digitally reconstructed into a model that you can analyze. The result is typically a waveform diagram, measuring oscillation amplitude over a period of time.

Analyze Your Data

This process begins by looking at the harmonics of your vibration data. Look at synchronous peaks, or high points in your vibration data that should repeat. The synchronous peaks correlate the frequency peak with the physical characteristics of the system, typically indicating a motor rotation or pumping cycle. Spikes in frequencies are completely normal, but peaks at an unexpected time or an unusually high peak are points to watch out for.

Types of vibration equipment & analysis tools

VA tools have grown from large bulky machines to lightweight handheld devices and continuous monitoring instruments. Continuous monitoring instruments have even joined the Internet of Things (IoT) galaxy.

Generally speaking, there are two types of devices that perform VA:

Portable devices

The strong magnet or wired connection is frequently used for portable collection devices. It allows the person collecting the data to measure many points with one machine and sensor. The portable device is a lower cost solution that has the added benefit of a technician making visual observations of an asset’s condition during collection.

Fixed devices

Fixed devices have two significant uses. They can be installed where it may be difficult or dangerous for a human to routinely reach the measurement points. Another valuable use of fixed vibration sensors is when continuous data is needed to provide a quick response to a critical piece of equipment.

Fixed devices are frequently found on high-speed equipment like compressors or turbines. This equipment can rapidly damage itself or the humans around it if a potential failure is not detected quickly.

How do vibration analysis tools work?

VA tools pick up the vibrations produced by equipment and measures their frequency (time between vibration pulses). They also measure how hard each vibration occurs. These measurements are compared with known problems and past equipment history.

Most VA tools work the same way. The difference is the process used in the collecting of the data. The process is separated by whether the data is collected using a portable device or a device linked to the monitoring software via a wired or wireless connection.

Data can be collected in two ways:

• Placing a strong magnet or other connection with a vibration sensor on an established asset location each time a measurement is made
• Installing a vibration sensor at a fixed location. The sensor can be connected to a data collector via a wire or through a wireless (IoT) connection

Example of vibration analysis

Vibration analysis on rotating equipment is more accurate when performed on the three axes of a drive train. For example, engineers at Inter Pipeline Ltd. of Alberta, Canada, were able to find the root cause of broken weldments using the power of VA when comparing their readings along the three axes of a pump. The story about Inter Pipeline’s success is documented here.

VA has multiple uses beyond traditional applications. It is often used to determine fan balances, drive belt conditions, and even pump cavitation.

How to use vibration analysis for predictive maintenance

Collecting data has to follow a specific pattern to be effective. The system measures known failure vibration frequencies and compares data taken at one time from another. Increasing vibration or its impact (how hard it vibrates) identifies a potential issue. This is why measuring at the same time is critical.

NOTE: VA data systems usually recognize the RPM of a machine. So it is not critical that a motor that was operating at 1,100 RPM during one collection is now operating at 1,600 RPM. It is only important that the data is collected within the normal operating speed of the equipment.

When using a portable device, the data collection process is usually called a Route.

A Route establishes:

1. The equipment to be measured
2. The location on the equipment where the measurement is needed
3. The types of tests required at each location

The data collected during the route is loaded into the VA database. The VA software helps to identify irregularities from previous data or is outside of a set parameter. (Rockwell offers a wide variety of VA solutions.)

The VA technician can take additional measurements and/or report the findings on a follow-up work order in the computerized maintenance management system (CMMS). The specific component requiring replacement or service can be made a part of the follow-up work if the technician is confident of the necessary next steps.

Benefits of Vibration Analysis

Vibration analysis is one of the most versatile tools in predictive maintenance programs. Some of the benefits for using vibration analysis to help you with data collection are:

• VA has a long history with a proven track record for reliability
• The potential for failure can be readily identified
• Data can be collected by anyone
• A portable collection route can be rapidly established
• There are multiple uses of VA beyond the most prevalent bearing failure search

Drawbacks of Vibration Analysis

It is clear that there are many strong use cases for and benefits that come from using vibration analysis as your method of data collection. Before getting started right away, it’s important to take into consideration any drawbacks that vibration analysis might bring:

• A VA system requires initial setup. (The effort can be reduced with a solid CMMS.)
• A VA champion needs to be trained and allowed to operate
• “Failed Bearings” are not easily recognized by many. The old test of spinning it in your hand cannot duplicate the pressures and speeds when most bearing failures are detected.