This blog post completes an 8-part series on vibration analysis written by Dr. Sara McCaslin & Nolan Crowley, Business Development Manager at HECO.
We hope you have enjoyed your journey.
Dr. Sara McCaslin: Sara has a Ph.D. in mechanical engineering from the University of Texas at Arlington. Sara has also taught materials science, manufacturing, and mechanical system design at the University of Texas at Tyler.
Nolan Crowley: Nolan has BS from Miami University along with extensive field experience with powertrains, electric motors, & vibration issues since 2007.
- Week 1: Vibration Analysis Training: Who’s Doing Your Analysis?
- Week 2: Vibration Analysis Equipment: Sensors and Hardware
- Week 3: Balancing Rotating Equipment: Static vs Dynamic
- Week 4: The Importance of Route-Based Data Acquisition
- Week 5: The Basics of Modal Analysis for Electric Motors and Powertrains
- Week 6: How to Setup Remote Monitoring Vibration Monitoring
- Week 7: The Place of Motion Amplification in Modern Vibration Analysis
- Week 8: Bidding/Specifying Your Vibration Analysis Program
Vibration analysis is a critical part of PdM (Predictive Maintenance) and condition-based maintenance when rotating machinery is involved. We’ve talked at length about various aspects of vibration analysis, but what you may not realize is that having a written/documented vibration analysis specification can offer a host of benefits.
There is no doubt that having a good vibration analysis program is beneficial. Consider the case of the California Orange County Treatment Plant 2 and Reclamation Plant 1, both of which saw a dramatic increase in reliability after using a clearly specified vibration analysis program.
Why Specifying an Analysis Program is Important
Your vibration analysis program should be clearly specified when you are shopping for a reliable PdM provider. By having your analysis program clearly documented, you can be sure that potential service providers have the tools and skills necessary to care for your equipment.
A clearly specified analysis program also serves to set very clear expectations for all parties involved, ensuring that your facility gets the information it needs and that your team will act on the information. And it helps keep those expectations realistic, especially when the specifications aren’t developed by just one person.
What Should Go into a Vibration Analysis Program Specification
Let’s talk about what a typical specification should include. This isn’t an exhaustive list, but it should help you get started.
Here are the basic guidelines for who should be performing vibration analysis:
- Anyone doing data collection should be certified to ISO 14386-2 Category II or higher
- Anyone actually analyzing the data and assessing machine condition should be (or be under under direction from someone) certified to ISO 14386-2 Category III or higher
Instrumentation Requirements (Hardware and Software)
At minimum, an FFT (Fast Fourier Transform) vibration analyzer will be needed. Here’s an example of some recommended specs and settings to obtain good data for vibration analysis:
- A dynamic range of 72 dB minimum.
- A Hanning window.
- A minimum of 4 linear averages, with a maximum overlap of 67%.
- Anti-aliasing filters
- Ability to store information
As to software used to program/analyze/store vibration data, it should be able to provide reports that can be opened using a recognized Window-based format (e.g., Word, Excel, pdf). In addition, the software needs to be able to store data including time waveforms, frequency spectrum, and trend data. In addition, all data files and reports should be suitable for electronic transfer (i.e., email, cloud-based storage, file transfer).
Measurement System Accuracy and Calibration
Accuracy is very important, and experts recommend that the vibration measurement system should have a ±5% measurement system amplitude accuracy over the selected frequency range. It should also be calibrated within one year prior to the date of measurement. In addition, calibration should be traceable to NIST (National Institute of Standards and Technology).
Vibration Sensor Requirements
Basic sensor requirements are more or less common sense: accelerometers, as opposed to hand-held transducers, should be selected and attached to the machine in such a way that (1) the minimum frequency and maximum frequency are within the usable frequency range of the transducer and (2) can be accurately measured.
Vibration Measurement Locations
Now let’s talk about where those accelerometers should be placed to obtain the best data. You will need to have a vibration analysis route that is followed regularly to obtain data for condition monitoring.
At each machine on the route, you should obtain ...
- A vertical and horizontal measurement at each bearing,
- At least one axial direction measurement for each machine component shaft (e.g., motor, pump, fan, compressor).
If there is an obstruction or safety concern that would make it difficult to correctly position an accelerometer, then place one as close as possible to the standard recommended position.
Next, vibration measurement locations should be on rigid, as opposed to flexible or moving, surfaces of the equipment and as close to each bearing as possible. That said, bearing housings, mounting blocks, and machine casings work very well. Flexible covers and shields are not good locations!
Finally, experts also recommend that, for ease of identification, measurement locations be numbered consecutively from 1 to N in the direction of power flow.
You can get pretty detailed with frequency ranges, as well. For starts, the frequency measurements should cover a range where upper frequency limit (Fmax) and lower frequency limit (Fmin) are enough to detect the following:
- Drive belts
- Mechanical looseness
- Gear mesh
So, how do you know what kind of frequencies are involved? Here’s a good rule of thumb:
- For fans, pumps, and motors: Fmax = 70 times running speed.
- For gear boxes: Fmax = 3.5 x the highest gear mesh frequency.
Vibration Analysis Measurement and Parameters
Let’s discuss some of the key measurements needed for successful vibration analysis. To start with, here are the basics:
- A time waveform measurement at each measurement location
- A FFT frequency measurement (in velocity units) at each measurement location
- For ball or roller bearing machines, demodulation or PeakVue™ time waveform and FFT measurement in 1 direction at each measurement location
As to the time waveform measurements, they need to be in acceleration units and based on the Fmax specified for FFT measurement. The velocity FFT measurements should have 800 lines of resolution minimum. They should use a Hanning window with a minimum of four linear averages and an overlap of 67% or less.
The demodulation or PeakVue FFT measurements are similar to those for velocity FFT measurements but not the same. Demodulation/PeakVue FFT should use a Hanning window and 3,200 lines of resolution, but should be in units of acceleration. Like velocity FFT measurements, they should use the Fmax specified for the FFT measurement, include a minimum of four linear averages, and have an overlap of 67% or less.
Reports serve as a communication tool between the vibration analysts and the operations and maintenance team. In a nutshell, the report (which should be submitted within a week of data collection) gives an overview of the status of key equipment, any changes in condition, and recommendations for a plan of action going forward.
A summary should be provided for all the machines that were evaluated, and a list of those which weren’t. Each machine should be clearly identified (e.g., asset number, equipment number, common name) and its condition should be described. The condition should be simple, like insignificant, significant, serious, or severe.
Beyond the summary, specific issues for each machine need to be described. If this is a repeat problem, then the date when it was first reported should be included as well. Data should also be provided to support the assessed condition. And the report should include recommendations for addressing the problem, whether it is additional monitoring or maintenance/repairs during the next planned shutdown.
Although not often included in the vibration analysis program specifications, it’s very important to make a commitment as to how the results of analysis are going to be handled. All the vibration analysis data won’t help with the reliability of your equipment if it’s ignored.
Having a solid vibration analysis program specification is an excellent start to condition-based monitoring and PdM that will increase the reliability of the equipment you are responsible for.
If you feel a little lost after reading the suggestions in this blog post, you can contact the experts at HECO! We can help you develop a solid vibration analysis program for your facility using the most up-to-date industry best practices. We also offer services such as balancing, motion amplification, and remote condition monitoring.