Setting Baseline References for Vibration Analysis
Vibration analysis is used to monitor the condition of rotating equipment and predict equipment issues based on data trends over time, abnormal frequencies or the amplitude of the measured vibration. The first step to successful vibration analysis is establishing relevant baseline references.
Experienced analysts typically use one of four methods, or a combination, to establish baseline references. The first method is a general approach that is based on the International Organization for Standardization (ISO) guidelines. The second method is to use data provided by the equipment manufacturer. Not all equipment manufacturers provide this data but when they do, it can be very helpful. The third method is individually tailored for specific equipment designs and can deliver customized alarms as needed. Finally, the fourth option is based on analyst and or engineer experience. Vibration analysis, while a science, can become an art form as many vibration engineers spend their careers learning the “signature” of various types of equipment. Thus, they have an internal reference they can use to supplement these other three options.
Regardless of which method is used, the first step in any vibration program is to gather as much information about the machine, its function, and the environment as possible. Drawings or machine schematics should also be obtained if possible. A good practice is to talk to everyone who interacts with the machine. This includes both management and maintenance personnel, as they can provide important machine insights. These critical clues often help to determine what is going on with the machine and can highlight potential issues. For example, you may learn that the machine has issues every time it rains outside. This information would guide the analyst to focus on issues surrounding moisture or humidity.
Method 1: Using ISO Guidelines
As mentioned, one method for setting baseline references is to use specifications from organizations such as ISO. They publish vibration specifications for certain types of equipment to be used as a guide. The ISO guidelines consider machine classes and how they qualify as a starting point for setting up baseline reference points. In recent years, this method has become the industry standard for setting baselines for vibration analysis.
In addition to these guidelines, some manufacturers have established baseline data for their equipment. This is the case for many pumps, fans and motors. At the component level, bearings also have well-established baseline data. This existing bearing data is very useful when analyzing equipment such as motors, reducers and pumps, each of which usually contain several bearings.
Method 2: Equipment Manufacturer
In addition to ISO guidelines, equipment manufacturers often generate and publish vibration information for their equipment or components. Fault frequencies are simply the known, or expected, frequencies or amplitudes a piece of equipment will produce when energized (operated). These frequencies are a result of the design of the component and/or equipment. Things like geometry, material and operational speeds have an impact.
Not all manufacturers produce and provide vibration data. However, it is very common among bearing manufacturers. Often, finding this data is as simple as doing an internet search for the component part number and the manufacturer.
Method 3: Statistical Analysis
This method takes into consideration that every piece of equipment is unique and may run slightly different than the next. Even the same model from the same manufacturer has manufacturing variations. Using the statistical analysis method, customized alarm limits are set based on statistical analysis of vibration data generated for the specific machine being monitored.
Algorithms are designed to detect negative trends, events and/or conditions based on the customer baseline. If readings are getting gradually worse, an alarm would be triggered. However, sometimes customers are concerned that a piece of equipment is already damaged or has already progressed toward failure prior to monitoring. The baseline set using ISO guidelines may not catch a preexisting condition or degradation and any manufacturer’s vibration information would only be applicable to equipment in a new, unused condition . If the vibration trend on the equipment rapidly deteriorates, it likely already had a problem. But, if the data doesn’t change, the alarm levels can be adjusted to establish a new alarm criteria. This type of customization allows for specifics of the equipment to be considered whereas generalized guidelines do not. Once baseline data is established, data trends can be tracked over time to predict equipment issues before they lead to failure.
Method 4: Experience
A final method for establishing equipment vibration baselines is experience. While vibration is a science and is backed by sound mathematics, it can also be a bit of an art. This is where an experienced vibration engineer or analysis is extremely valuable. The experienced vibration engineer can recognize equipment types, operational aspects and environmental conditions that may need to be taken into consideration. Experience often is not the primary source for setting a baseline, however it is almost always a complementary piece of the process and should be utilized when possible.