REGISTER NOW! August 1, 2022. FREE 1–Hour Virtual Uptime Elements Introduction

The vibration at the surface of the bearing housing has a great story to tell. It can tell you about the smallest spall on the surface of a bearing, it can tell you about damaged rotor bars, it can tell you about worn teeth in the critical gearbox, and so much more - but you'll never know unless you take the measurement correctly.

There are two main opportunities to make mistakes: the mounting of the accelerometer, and the settings used by the analyzer.

Mounting the accelerometer

There are a few simple rules:

1. Mount the accelerometer at a location with a good transmission path to the bearing. Fins, covers, and brackets are not good locations.

2. Mount the accelerometer in the same place every time. Repeatability is essential.

3. Prepare a clean flat surface on the bearing or use a mounting pad. If you are interested in high frequency vibration (and you should be!) you should use flat magnets, quick-connect mounts, or stud mounts.

Analyzer settings

There are a few simple rules:

1. Make sure the Fmax is high enough to cover 3.5 times the highest forcing frequency of interest (e.g. gearmesh), and at least 10 times the highest bearing frequency expected. This ensures you don't miss any harmonics. If you don't know the highest frequency generated by the bearings, you should be safe by using an Fmax of 70 times the turning speed of the shaft.

2. Make sure the resolution is sufficient to identify all the individual frequencies and sidebands. 3200 lines is a good place to start.

3. Make sure you take plenty of averages, especially if you use overlap averaging (- and you should). The shaft of the machine should turn at least 50 times during your measurement (and if you were to test it again immediately the data should look the same). For example: 1800 RPM machine, Fmax: 3000 Hz, Overlap: 67%, Averages: 5 - there are 75 shaft rotations. That's good.

4. Consider acquiring two measurements so that you can quickly and easily identify unbalance, misalignment, looseness, resonance and other faults AND gearbox, motor, bearing, and cavitation faults without having to toggle units or zooming the frequency scale:

a. Fmax: 70 times the turning speed and units of acceleration

b. Fmax: 10 times the turning speed and units of velocity

Remember, just because the spectrum you view in the analysis software looks like a normal spectrum does not mean the measurement was taken correctly. That's the problem with vibration analysis; it is hard to tell when you are making mistakes (unless the machine fails unexpectedly).

There is a great deal more we could say on this important topic, but hopefully these comments will give you something to think about.

Tip provided by Jason Tranter, Managing Director, Mobius Institute

Upcoming Events

August 9 - August 11 2022

MaximoWorld 2022

View all Events
banner
80% of Reliabilityweb.com newsletter subscribers report finding something used to improve their jobs on a regular basis.
Subscribers get exclusive content. Just released...MRO Best Practices Special Report - a $399 value!
DOWNLOAD NOW
Reliability Leader Fluid Cleanliness Pledge

Fluid Cleanliness is a Reliability Achievement Strategy as well as an asset life extension strategy

MaximoWorld 2022 Conference Austin Texas

Connect with leading maintenance professionals, reliability leaders and asset managers from the world's best-run companies who are driving digital reinvention.

“Steel-ing” Reliability in Alabama

A joint venture between two of the world’s largest steel companies inspired innovative approaches to maintenance reliability that incorporate the tools, technology and techniques of today. This article takes you on their journey.

Three Things You Need to Know About Capital Project Prioritization

“Why do you think these two projects rank so much higher in this method than the first method?” the facilitator asked the director of reliability.

What Is Industrial Maintenance as a Service?

Industrial maintenance as a service (#imaas) transfers the digital and/or manual management of maintenance and industrial operations from machine users to machine manufacturers (OEMs), while improving it considerably.

Three Things You Need to Know About Criticality Analysis

When it comes to criticality analysis, there are three key factors must be emphasized.

Turning the Oil Tanker

This article highlights the hidden trap of performance management systems.

Optimizing Value From Physical Assets

There are ever-increasing opportunities to create new and sustainable value in asset-intensive organizations through enhanced use of technology.

Conducting Asset Criticality Assessment for Better Maintenance Strategy and Techniques

Conducting an asset criticality assessment (ACA) is the first step in maintaining the assets properly. This article addresses the best maintenance strategy for assets by using ACA techniques.

Harmonizing PMs

Maintenance reliability is, of course, an essential part of any successful business that wants to remain successful. It includes the three PMs: predictive, preventive and proactive maintenance.