Introduction
Condition monitoring is the practice of monitoring parameters that determine the operating condition of machinery. This process predicts impending equipment failure by noting significant changes in machinery behavior. Condition monitoring is a significant component of predictive maintenance, where scheduled maintenance can be used to prevent equipment failure, before it occurs. The prediction of the time of failure is a cost-effective means of maintaining rotating machinery and stationary machinery, such as boilers and heat exchangers.
Vibration Monitoring in Rotating Machinery
Monitoring vibration in rotating machinery is an important aspect of condition monitoring. The vibration signatures in rotating machinery can be complex, so specialized training and experience is necessary to interpret the data. Today’s technology, however, automatically provides the analyst with the necessary parameters to allow assessment of equipment vibratory behavior. Analyzing vibration data is typically a matter of interpreting the frequency content and amplitude of the vibration signal. The vibratory frequencies typically can be interpreted in lieu of mechanical component performance. These components include rolling element bearings and out-of-balance or misaligned shafts.
Analyzing the Vibration Frequency Content
Vibration frequencies and amplitudes usually tell a story. For example, frequencies that correspond to the equipment’s rotational speed usually indicate an imbalance that can be corrected by rebalancing the machine. Rolling element bearings usually exhibit increasing vibratory amplitudes at specific frequencies. These frequencies usually indicate a bearing that is wearing out. When this occurs, the bearing can be replaced, before total equipment failure occurs. This type of maintenance activity is very cost-effective, as the cost of machinery down time can be very large.
Analyzing the Vibration Amplitude
Today’s vibration data collectors utilize a Fast Fourier Transform (FFT) to convert the time domain vibration signal into a frequency domain signal. Utilizing the frequency content (spectral analysis) is only one method of interpreting machinery vibration data. Depending on the equipment type, a maintenance analyst may also use the time domain data, historical trends, the shape of the vibration signal, and the phase relationships between various amplitudes.
Measuring Vibration with Handheld Data Collectors
Advances in technology and computer software now allow the technician to take measurements using handheld data collectors. This greatly simplifies the data collection process, and can allow for data analysis on site. Larger equipment may still require a dedicated vibration monitoring system, but many equipment types can be analyzed using handheld data collectors. Using either method of data collection, the diagnostic tools are generally the same.