A vibration monitoring system is a complete system that is capable of acquiring vibration signals according to pre-determined parameters such as sampling frequency, vibration level, recording length, recording intervals and frequency bandwidths. The system should be able to process the recorded vibration and translate the information to intuitive indications for the machine operators, maintenance staff or asset managers.
The system should not interfere the normal operation of the machines or structures that are being monitored and the benefits of the system should be higher than the cost of implementing the system.
Vibration Monitoring on Rotating Machinery
Vibration monitoring on rotating machinery is a critical practice in predictive maintenance and condition monitoring. It involves using sensors to measure the vibrations produced by rotating machines, such as motors, pumps, turbines, compressors, and fans. Monitoring vibration levels and frequencies helps detect early signs of mechanical issues like imbalance, misalignment, bearing wear, and other faults before they lead to costly failures or unscheduled downtime.
How Vibration Monitoring Works and its Key Elements:
1. Vibration Measurement
Sensors: The most common sensor used for vibration monitoring is an accelerometer. These devices are placed on or near the machinery's bearing housings, shafts, or casings to detect movement in terms of acceleration, velocity, or displacement.
Units of Measurement:
Acceleration: Measured in meters per second squared (m/s²) or g (gravitational force units), this measures the rate of change of velocity.
Velocity: Measured in millimeters per second (mm/s), this provides insight into the dynamic forces acting on the machine.
Displacement: Measured in micrometers (µm), this tracks the distance the component moves relative to its resting position.
2. Data Collection and Analysis
Continuous vs. Periodic Monitoring: Some systems continuously monitor vibration levels, while others may take periodic readings based on the criticality of the machine or asset.
Frequency Spectrum: Vibration data is typically analyzed in the frequency domain using Fast Fourier Transform (FFT) analysis. This helps identify specific fault frequencies that correspond to certain mechanical issues (e.g., bearing faults, gear mesh defects, etc.).
Time Domain vs. Frequency Domain: Vibration signals can be analyzed in both time and frequency domains, with frequency domain analysis being particularly useful for identifying periodic faults, like imbalance or bearing defects.
3. Common Faults Detected via Vibration Monitoring
Imbalance: Imbalance occurs when a rotating part has uneven mass distribution. This can cause excessive vibration at specific frequencies related to the speed of the machine.
Misalignment: Misalignment happens when the rotating shafts are not properly aligned, leading to increased stress on components, which manifests as vibrations at certain harmonic frequencies.
Bearing Wear/Faults: Bearing problems (e.g., pitting, spalling, or contamination) can produce characteristic vibration patterns, such as repeating impacts or high-frequency noise.
Looseness: Loose components (e.g., bolts, mounts, or housing) can generate high vibration levels and even lead to more severe damage if not addressed.
Gearbox Faults: Gear mesh problems, such as tooth wear or broken teeth, also create characteristic vibrations.
4. Vibration Thresholds and Alarming
Baseline Data: The first step in effective vibration monitoring is to establish baseline vibration levels for the machinery in question. These baseline values serve as references for detecting anomalies.
Alarm Limits: Based on the baseline data and the nature of the equipment, thresholds are set to trigger alarms when vibration levels exceed predefined limits. These thresholds can be based on vibration velocity, acceleration, or displacement.
Severity Levels: Some systems allow for the classification of vibration severity into categories (e.g., green, yellow, red) to indicate the urgency of maintenance or investigation.
5. Types of Vibration Monitoring Systems
Standalone Systems: These systems monitor individual machines, with sensors placed directly on the equipment. Data can be stored locally or sent to a central monitoring station.
Wireless Monitoring: Increasingly popular due to ease of installation and reduced cabling costs, wireless vibration sensors transmit data to a central hub or cloud-based system for remote analysis.
Integrated Systems: In some advanced setups, vibration monitoring is part of a larger condition monitoring system, often integrated with other sensors like temperature, pressure, and acoustic sensors to provide a more comprehensive picture of machine health.
6. Benefits of Vibration Monitoring
Predictive Maintenance: By identifying faults early, vibration monitoring allows for planned maintenance, reducing unplanned downtime and extending the life of the machinery.
Cost Savings: Early detection of faults helps avoid expensive repairs or catastrophic failures, which can be significantly more costly than preventive maintenance.
Improved Safety: Reducing unexpected machine failures helps to maintain a safer working environment by preventing accidents or damage to other equipment.
Optimized Performance: Monitoring and correcting vibration issues improves machine performance, energy efficiency, and product quality.
7. Vibration Monitoring Techniques
Time Waveform Analysis: Direct measurement of the vibration signal over time. Useful for detecting transient events and for low-frequency fault detection.
FFT (Fast Fourier Transform) Analysis: Converts the time-domain signal into frequency domain data, where different frequency components of the vibration can be analyzed for specific fault frequencies.
Envelope Analysis: Used primarily to detect early bearing failures, this technique highlights modulations in the vibration signal caused by rolling element impacts.
8. Limitations and Challenges
Environmental Interference: External factors, like temperature fluctuations, electrical noise, or nearby machinery, can affect vibration readings and lead to false alarms or missed detections.
Data Overload: In large systems with many machines, vibration data can become overwhelming. Effective data filtering and prioritization are key to ensuring useful insights.
Initial Setup Costs: While the cost of sensors has decreased, installing a comprehensive vibration monitoring system (especially one with wireless or real-time capabilities) can require significant investment.
Conclusion
Vibration monitoring on rotating machinery is a highly effective way to predict and prevent machine failures by providing real-time insights into the mechanical health of equipment. By detecting problems early, businesses can perform targeted maintenance, reduce downtime, and improve operational efficiency. Modern systems are becoming increasingly sophisticated, offering more detailed analytics and integration with broader maintenance strategies, including IoT-enabled devices and cloud-based platforms.