Machinery Lubrication

24 Reliable Plant | www . reliableplant.com Machinery Lubrication | www . machinerylubrication.com 2025 Annual VIBRATION ANALYSIS detecting machine faults like misalignment or unbalance. • Phase measurement: When talking about vibration analysis, phase is a relative time difference between two signals measured in units of angle as opposed to time. It only works if the two signals being compared are of the same frequency. Phase measurement is used in tandem with FFT to decipher machine faults like loose parts, misalignment and unbalance. • Order analysis: Order analysis is a variation of FFT analysis and is mostly used to quantify vibrations of machines with varying revolutions per minute (RPM). In other words, order analysis is frequency analysis where the spectrum's frequency axis is shown in orders of RPM rather than hertz. e term "orders" refers to a frequency that is a multiple of a reference rotational speed. For example, if a vibration signal is equal to twice the frequency of the motor's rotation, the order is two. • Power spectral density (PSD): Power spectral density is calculated by multiplying the amplitude from the FFT by its different forms to normalize it with the frequency bin width (bin width refers to the grouped x-axis values). ink of PSD as looking at "random" vibrations or motion at many different frequencies. PSD accurately compares random vibration signals that have different signal lengths. • Envelope analysis: Envelope analysis is a form of vibration analysis that can detect impacts with very low energy often hidden by other vibration signals. It's a popular diagnostic tool for damaged gear teeth and roller bearings. • Orbit: e orbit is defined as a plot of a sleeve bearing journal's centerline. It's measured by placing two probes in the bearing housing 90 degrees apart. Data from these probes can be displayed digitally and used to detect shaft vibrations caused by oil whirl - oil whirling around inside, causing the journal to move. • Resonance analysis: Resonance analysis identifies all the natural vibrations and frequencies in machines. e presence of resonance means high vibration, which could reach damaging levels. CATEGORIES OF VIBRATION MEASUREMENT • Overall level of vibration: You can think of checking the overall level of vibration like a "rough check" on a machine. By feeling a machine with your hand, you can determine a general sense of whether it is running roughly over a wide frequency band. is initial check is best on rotating machinery, in particular high- speed machines. It's not usually applicable to reciprocating machines. • Spectral analysis of vibration: Spectral analysis is the process of transforming a signal from the time domain to the frequency domain. It's often done using FFT. e signal is analyzed to determine any substantial frequen- cies coming from the machine's components. Where there is a peak in frequency signal, that is the likely source of vibration. Common applications for spectral analysis include the rotational speed of a shaft or how often tooth meshing occurs on a pair of gear wheels. • Discrete frequency monitoring: If you need to monitor a specific component within a machine, discrete frequency monitoring measures the vibration level being generated at a particular frequency which that component would be expected to generate. For example, if you want to look into a certain shaft in a machine, you would turn the monitoring to that machine's rotational speed. Discrete frequency is calculated using the FFT algorithm. • Shock pulse monitoring: Shock pulse monitoring is a predictive maintenance technique that monitors rolling-element bearings with a hand-held instrument. e hand-held instrument gives off a natural frequency that is excited by shocks or vibrations generated by rolling bearings. In other words, when two pieces of metal touch each other while in motion, shock waves develop from the impact, which travels through the metal. is shockwave is used in shock pulse monitoring. • Kurtosis measurement: Kurtosis gives you a measure of the "spikedness" of a Power Density vs. Frequency

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