Understanding Vibration Analysis (VA)

1. Definition: What is Vibration Analysis?

Vibration Analysis (VA) is a broad technical discipline and a key process within vibration diagnostics. It refers to the specific techniques used to measure, process, and interpret the vibration signatures of rotating machinery. The primary goal of vibration analysis is to detect faults and identify their nature and severity, making it a cornerstone of predictive and proactive maintenance programs.

2. The Core of Vibration Analysis: FFT

While many techniques exist, modern vibration analysis is built upon the Fast Fourier Transform (FFT). The FFT is a highly efficient algorithm that takes a complex time waveform signal—which is difficult to interpret by eye—and deconstructs it into its individual frequency components.

The result is a spectrum, a graph that plots the amplitude of vibration at each specific frequency. This spectrum is the vibration analyst’s most powerful tool, as different mechanical and electrical faults manifest as distinct patterns and peaks on this graph.

3. Key Techniques in Vibration Analysis

Vibration analysis is not a single activity but a collection of specialized techniques, each providing a different view of the machine’s health:

• Overall Level Monitoring: The simplest form of VA, where a single value (usually RMS velocity) representing the total vibrational energy is trended over time. A sharp increase indicates a problem, but not the specific cause.
• Spectral Analysis: The detailed examination of the FFT spectrum to identify the frequencies of vibration. This is used to diagnose the root cause of the problem (e.g., unbalance, misalignment, etc.).
• Time Waveform Analysis: The direct analysis of the raw vibration signal over time. It is particularly useful for identifying transient events, impacts, and certain non-linear behaviors that are not always clear in the FFT spectrum.
• Phase Analysis: The measurement of the relative timing between a vibration signal and a reference point. It is indispensable for one-shot balancing, confirming misalignment, and distinguishing between different types of faults.
• Envelope Analysis: A specialized signal processing technique used to detect low-energy, repetitive impacts characteristic of early-stage rolling-element bearing and gear faults.
• Modal Analysis and ODS Analysis: Advanced techniques used to understand the structural vibration characteristics of a machine or its foundation, primarily to identify and solve resonance problems.
• Order Analysis: An adaptation of spectral analysis for machines that change speed. It presents the spectrum in terms of “orders” (multiples of running speed) instead of absolute frequency (Hz).

4. Applications and Benefits

Vibration analysis is applied across virtually every industry that uses rotating equipment, including manufacturing, power generation, oil and gas, and transportation.

The benefits of a well-implemented vibration analysis program are significant:

• Increased Uptime: By detecting faults early, maintenance can be scheduled before a catastrophic failure occurs, avoiding unplanned downtime.
• Enhanced Safety: Prevents equipment failures that could pose a risk to personnel.
• Reduced Maintenance Costs: Eliminates unnecessary “preventive” maintenance on healthy machines and reduces the cost of repairs by catching problems before extensive secondary damage occurs.
• Improved Asset Reliability: Moves maintenance from a reactive or scheduled-based model to a condition-based approach, maximizing the life and performance of machinery.

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