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Articles: Vibration Analysis

2009 PdM Program of the Year Award Winners

Primetime Programs receive award from Uptime Magazine

A Better Understanding of Rotor Dynamics and Support Stiffness

More Data Provides More Answers

by Ron Brook

A Look into Pulse Theory And Why the Walls of Jericho Fell

An excerpt from the book Vibration Spectrum Analysis by Steve Goldman P.E.

This author has spent many years lecturing to different groups of people who were interested in spectrum analysis for problems ranging from detailed physical tests of cavitation phenomena to philosophical questions about why the walls of Jericho Fell. Often, a very simple explanation involving pulse theory has sufficed to explain some of the observed phenomena. This excerpt is designed to give the reader food for thought rather than quantitative answers.

A Tough Diagnosis - The Saga of the Never Ending Problem

by Greg Davison

You are often told that there is never just one problem with a machine. My very first vibration class taught me that a phase and magnitude vector was a combination of all the vibration from all of the forces acting upon the machine. Likewise, a spectrum also contains all of the frequencies from all of the forces acting upon a machine. So, it is never just imbalance, or just misalignment. It is always some combination of many forcing frequencies. This is precisely why wall charts and cookie cutter solutions do not always work. What follows is a story of multiple problems of mythical proportions.

 

An Introduction to Time Waveform Analysis

In recent years there has been a resurgence in the use of time waveform analysis techniques. Condition monitoring personnel have now come to realize some of the limitations of the FFT process. Since many find the time waveform analysis process difficult and confusing the technique is rarely used to its full potential. The key to the successful utilization of time waveform data is knowing when to use it. This paper examines the limitations of the FFT process and identifies specific applications where enhancing FFT information with time waveform analysis is appropriate.

The paper also details in practical terms how to set up, acquire and manipulate time waveform data. Having discussed the acquisition of the data the paper continues to discuss the interpretation of the data including the time-frequency relationship, symmetry, and pattern recognition of common faults.

Balancing a Generator at a Hydro Electric Plant

Just two years after installation of a new turbine-generating unit at the 93-MW Thompson Falls hydro project, PPL Montana LLC noticed increasing vibration values on the generator guide bearing. After several unsuccessful attempts to correct the problem, plant personnel adjusted the clearance on the guide bearings. Since that work was completed, the unit has operated within acceptable vibration values.

Belt Faults

Belt drives can cause many strange looking spectra. To analyze and troubleshoot belt drives it is imperative to have a high resolution analyzer. I use one with 3200 lines of FFT. To those still using 400 lines that might seem like overkill. This paper, though, will show the necessity of high resolution when troubleshooting many vibration problems.

Diagnosing Tiny Bubbles

Vibration Signatures of Cavitation in a Centrifugal Pump

by Dr. Lin Liu & Dr. Suri Ganeriwala

Cavitation is a major source of problems in centrifugal pumps.  If it is not detected early enough, it can even destroy a pump.  Vibration analysis is often used to determine the cavitation, but its vibration signature is still elusive.

Flake Breaker Vibration Analysis Case Study

by Ronald Blay, Lead Analyst, Allied Reliability - Cargill Oil Seed, Fayetteville, NC

This is a Flake Breaker Vibration Analysis Case Study at the Cargill Salt Division Watkins Glen plant 

Great Savings for Great River

Continuous Monitoring Lowers Costs, Boosts Performance

by Robert Skeirik and Craig Truempi

The ability of continuous vibration monitoring to provide early detection of potential bearing problems in rotating equipment allows users to plan maintenance work in advance.  This maximizes uptime by minimizing the impact of costly machine break downs.

How is Machine Vibration Data Collected?

By Commtest Instruments

As machine surroundings are often hazardous and uncomfortable, vibration analysis is normally performed away from the machine. To do this, measurements are usually recorded with the instrument then transported to an office where the recorded data can be analyzed in a quiet and safe environment. In the office, the data can be transferred to a computer for more detailed analysis.

How is Machine Vibration Described?

By Commtest Instruments

To analyze the condition of a machine you first need to accurately describe the behavior or symptoms of the machine.

How can vibration symptoms be described accurately?

How do vibration analysts describe the condition of a machine?

In this section we present the basic methods of describing machine vibration.

After reading this section you will:

• Know the two most important methods of describing machine vibration
• Understand the term 'amplitude'
• Understand the term 'frequency'
• Understand what a spectrum or waveform is

 

 

How is Vibration Measured?

By Commtest Instruments

In the last section we identified the most important vibration analysis tool as the spectrum. When we measure machine vibration we usually measure vibration spectra, since the spectrum of a vibrating component tells us a great deal about the condition of the component as well as about the cause of vibration. Naturally it is vital that the spectrum, which gives such valuable information, be obtained accurately.

What guidelines must be observed to ensure measurements are accurate? How should measurements be taken and for which machines should they be taken?

If the Bearing is Hot: (It might be greased or not)

"Vibration analysis" is commonly used to assess bearing condition however, although the vibration data can appear ok, there are other conditions which can exist or be unknowingly created to open the door for potential failure.

I am referring to bearing lubrication. This is an area where although, information by the bucket full can be easily obtained, Practicing the art of proper bearing lubrication tends to be ignored, not practiced or severely misunderstood. Usually, one step in a PM requires maintenance personnel to grease the bearings. This practice has become acceptable because we all know what happens when there is not enough grease so...we apply the old rule of thumb that is; "better to have too much grease than not enough" right? The problem is... we really aren't sure how many times or the last time a bearing on a particular machine got greased. It has been said over and over again that over greasing can cause more damage. Unless some system has been put into place to record the greasing activity, we can never be 100% sure. I will demonstrate through the use of infrared technology what the outcome will be if over lubrication happens.

Measuring Shock Pulse another approach to Front Line Condition Monitoring

Downtime in a paper mill or any 24/7 facility is very expensive in maintenance costs, but even more so in the impact to profit because of production loss. In this article we will explain the Shock Pulse Method, why it's a good choice for frontline vibration measurement and show the resulting savings that the Hallsta Mill in Sweden realized from utilizing it as the primary component of its Condition Based Maintenance Program.

Hallsta personnel determined these calculations when they looked at the number of incidents in which they were able to perform maintenance in a planned shutdown, instead of taking the equipment (and production line) down.

Condition monitoring should always start with a list of machine faults, specific for each machine. Only if you know exactly what you expect from the monitoring method, can you apply it efficiently and correctly. Otherwise, there is a danger that you will simply be collecting data. And data is of no use unless it is converted to useful information that you can act upon to realize your true goal of maintaining plant equipment in good working order.

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