If you have been in the vibration industry for any length of time you have noticed many of the same catchphrases and acronyms have polluted what should be a simple science of vibration analysis. When setting up a vibration program there is one important word to remember. This word has been hidden over the last decade and not everyone has forgotten it, but some people have overlooked it, or have been distracted by all the bells and whistles of certain vibration tools. The word is TIME. With newer technology and advances in data collection speed, it is very easy to collect more data at quicker speeds. But is this a good thing? Refer back to the most important word: TIME. Now you can collect 10× the amount of data in the same time that it took four years ago. While that is good, someone still needs to look at all that data. Looking at a lot of data takes time. Reporting on a lot of data takes time. Time is money and the smarter use of time means saving or making more money. If you are a novice setting up a vibration program, or if you have had a successful vibration program for years, it is very important to maximize your time. Mean Time Between Failures (MTBF) is a common acronym that is tossed around a lot. The key word, of course, is time. The definition of MTBF depends upon your definition of a system failure. A system failure may be defined as any component failure in a machine. However, a system failure could be defined as a component failure that prevents the machine from operating in the desired way. MTBF is the average elapsed time between such failures and should be calculated from a sufficiently large sample size of failures to be statistically meaningful. You can determine the MTBF for your equipment failures and use this as a tool to determine the monitoring frequency required for your vibration analysis program. You should make sure that you collect the vibration data on the specified equipment at a time interval that allows your vibration program sufficient time to identify the causes of equipment failures before the failures occur. If the MTBF, as an example, of a specific failure is seven weeks and you collect data every 12 weeks, then your vibration program will most likely not be able to identify that failure. It is critical that you select the correct measurement period for the equipment faults you wish to identify. It is recommended that three measurement points be collected on each bearing or measurement location. It may be possible to collect data on fewer measurement points to save time. Once a problem has been detected, then additional data can be collected to verify the issue. Another technique is to use measurement bands in your data collection. The VibXpert series of data collectors allows this technique to be used. This method lets you customize the data acquisition around the specific failure modes (bearing, gears, imbalance, alignment, etc) of the equipment being monitored. This reduces the amount of data collection required, makes the data acquisition faster and provides more analysis capabilities. All of this will save you time. Correct alarm settings can save analysis and reporting time. Correct setup of alarm levels for measurement bands can allow problems to be identified more quickly and accurately. This can save you time as well. It is important that you spend the required time to identify the correct measurement bands and alarm levels for each machine. Failure to do so may create the opposite result and increase the time required to acquire, analyze data and report the findings. This knowledge will allow you to find the correct measurement period to identify the necessary equipment faults. Some of the things that are discussed in this post will hopefully generate feedback. Please post your comments and let us know what you think.
Vibration Analysis by Mickey Harp CRL