Glossary Archive • Page 2 of 2 • Portable balancer, vibration analyzer "Balanset" for dynamic balancing crushers, fans, mulchers, augers on combines, shafts, centrifuges, turbines, and many others rotors Glossary Archive • Page 2 of 2 • Portable balancer, vibration analyzer "Balanset" for dynamic balancing crushers, fans, mulchers, augers on combines, shafts, centrifuges, turbines, and many others rotors

Glossary

Vibration diagnostics and rotor balancing glossary

What is Eccentricity in Rotating Machinery?

Understanding Eccentricity in Rotating Machinery Definition: What is Eccentricity? In the context of rotor dynamics, eccentricity refers to the radial distance or offset between a rotor’s center of mass (also called the center of gravity) and its geometric center (the true center of its form or shaft). In a perfectly Read more
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What is an Eddy Current Probe? Non-Contact Displacement Sensor

Understanding Eddy Current Probes Definition: What is an Eddy Current Probe? Eddy current probe (also called proximity probe, non-contact displacement sensor, or eddy current transducer) is a sensor that measures the distance (gap) between the probe tip and a conductive target surface without physical contact. In vibration monitoring, eddy current Read more
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Diagnosing Electrical Faults with Vibration Analysis

Diagnosing Electrical Faults in AC Motors 1. Introduction: Electrical Faults as a Vibration Source While vibration analysis is typically associated with mechanical faults like unbalance and bearing defects, it is also a very powerful tool for detecting problems within AC induction motors. Electrical faults generate pulsating magnetic forces that cause Read more
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What is Electrical Frequency? Line Frequency in Motors

Understanding Electrical Frequency in Motors Definition: What is Electrical Frequency? Electrical frequency (also called line frequency, mains frequency, or power frequency) is the frequency of the alternating current (AC) supplied to electric motors and other electrical equipment. The two standard electrical frequencies worldwide are 60 Hz (Hertz) in North America, Read more
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What is Electrical Unbalance? Phase Imbalance in Motors

Understanding Electrical Unbalance Definition: What is Electrical Unbalance? Electrical unbalance (also called phase unbalance, voltage unbalance, or current unbalance) is a condition in three-phase electrical systems where the voltages or currents in the three phases are not equal in magnitude or are not separated by exactly 120 electrical degrees. This Read more
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Envelope Analysis for Bearing Fault Detection

Envelope Analysis (Demodulation) for Early Fault Detection Definition: What is Envelope Analysis? Envelope analysis, also known as demodulation or high-frequency enveloping, is a powerful signal processing technique used in vibration analysis to detect early-stage faults in rolling-element bearings and gearboxes. These types of faults, such as microscopic cracks or spalls, Read more
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What is an Envelope Spectrum? Demodulated Signal Analysis

Understanding Envelope Spectrum Definition: What is an Envelope Spectrum? Envelope spectrum is the frequency spectrum obtained by computing the FFT of the envelope (amplitude-demodulated) signal from envelope analysis. It reveals the repetition rates of impacts or modulations in high-frequency vibration, making it the most powerful technique for detecting rolling element Read more
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What are Fan Defects? Common Failures and Diagnosis

Understanding Fan Defects Definition: What are Fan Defects? Fan defects are faults in industrial fans and blowers including blade damage (cracks, erosion, buildup), unbalance from material loss or accumulation, aerodynamic instabilities (stall, surge), structural problems (loose blades, cracked hubs), and bearing/drive failures. These defects create characteristic vibration patterns dominated by Read more
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What is Mechanical Fatigue? Cyclic Stress Failure

Understanding Mechanical Fatigue Definition: What is Mechanical Fatigue? Mechanical fatigue (also called material fatigue or simply fatigue) is the progressive, localized structural damage that occurs when a material is subjected to repeated cycles of stress or strain, even when the maximum stress in each cycle is well below the material’s Read more
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What is Fault Detection? Problem Identification

Understanding Fault Detection Definition: What is Fault Detection? Fault detection is the process of identifying that a defect or abnormal condition exists in equipment through analysis of monitored parameters such as vibration, temperature, performance metrics, or other indicators. Fault detection answers the binary question “Is there a problem?” before proceeding Read more
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What is Field Balancing (In-Situ Balancing)?

Understanding Field Balancing (In-Situ Balancing) Definition: What is Field Balancing? Field balancing, also known as in-situ balancing, is the process of correcting the unbalance of a rotor while it is running in its own bearings and support structure, at or near its normal operating speed. Unlike shop balancing, where the Read more
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What is a Flexible Rotor?

Understanding a Flexible Rotor Definition: What is a Flexible Rotor? A flexible rotor is a rotor that deforms or bends due to centrifugal forces when operating at or near its critical speeds. Unlike a rigid rotor, which can be balanced at a low speed and will remain balanced throughout its Read more
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What is Flow Turbulence? Unsteady Flow Vibration

Understanding Flow Turbulence Definition: What is Flow Turbulence? Flow turbulence is chaotic, irregular fluid motion characterized by random velocity fluctuations, swirling eddies, and vortices in pumps, fans, compressors, and piping systems. Unlike smooth laminar flow where fluid particles move in ordered parallel paths, turbulent flow exhibits random three-dimensional motion with Read more
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What is Forced Vibration? External Excitation Response

Understanding Forced Vibration Definition: What is Forced Vibration? Forced vibration is oscillatory motion caused by an external periodic force applied to a mechanical system. The vibration occurs at the frequency of the applied force (forcing frequency), and the amplitude is proportional to the magnitude of the forcing function and inversely Read more
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What is Foundation Stiffness? Structural Dynamics

Understanding Foundation Stiffness Definition: What is Foundation Stiffness? Foundation stiffness is the resistance of a machine’s support structure (including baseplate, concrete foundation, pedestals, and soil) to deflection when subjected to static or dynamic forces. It is quantified as force per unit deflection (typically expressed in N/mm, lbf/in, or N/m) and Read more
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What is the Four-Run Method in Rotor Balancing?

Understanding the Four-Run Method in Rotor Balancing Definition: What is the Four-Run Method? The four-run method is a systematic procedure for two-plane balancing that uses four distinct measurement runs to establish a complete set of influence coefficients for both correction planes. The method involves measuring the rotor’s initial condition, then Read more
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What is Frame Resonance? Machine Structure Vibration

Understanding Frame Resonance Definition: What is Frame Resonance? Frame resonance is a specific type of structural resonance where the machine’s own structural frame, housing, casing, or enclosure vibrates at one of its natural frequencies in response to excitation from the rotating components. Unlike foundation or pedestal resonances which involve the Read more
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What is a Frequency Response Function (FRF)?

Understanding the Frequency Response Function (FRF) 1. Definition: What is a Frequency Response Function? The Frequency Response Function (FRF) is a measure that describes how a structure, component, or system responds to an applied excitation force, as a function of frequency. In simpler terms, the FRF tells you how much Read more
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What is Frequency in Vibration Analysis?

Understanding Frequency in Vibration Analysis Definition: What is Vibration Frequency? Frequency is a measure of how often a repetitive event occurs in a given unit of time. In vibration analysis, it quantifies “how fast” an object is oscillating or vibrating. It is the single most important parameter for diagnosing the Read more
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What is FTF? Fundamental Train Frequency in Bearings

Understanding FTF – Fundamental Train Frequency Definition: What is FTF? FTF (Fundamental Train Frequency, also called cage frequency or retainer frequency) is one of the four fundamental bearing fault frequencies, representing the rotational speed of the bearing cage (also called separator or retainer) that holds the rolling elements in position Read more
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What are Balance Quality Grades (G-Grades)?

Understanding Balance Quality Grades (G-Grades) Definition: What is a Balance Quality Grade? A Balance Quality Grade, commonly referred to as a G-Grade, is a classification system defined by ISO standards (specifically ISO 21940-11, which superseded the older ISO 1940-1) to specify the acceptable limit of residual unbalance for a rotor. Read more
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Diagnosing Gear Defects with Vibration Analysis

Diagnosing Gear Defects 1. The Vibration Signature of Gears Gears are a fundamental component for power transmission in industrial machinery. The meshing of gear teeth is an inherently noisy and vibrant process. Healthy gears produce a very clear and stable vibration signature, and deviations from this signature are a strong Read more
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What is Gear Mesh Frequency? Gearbox Diagnostics

Understanding Gear Mesh Frequency Definition: What is Gear Mesh Frequency? Gear mesh frequency (GMF, also called tooth mesh frequency or tooth engagement frequency) is the vibration frequency generated by the engagement of gear teeth as they enter and exit contact during gear rotation. It is calculated as the number of Read more
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What is Gear Wear? Types and Detection Methods

Understanding Gear Wear Definition: What is Gear Wear? Gear wear is the progressive loss of material from gear tooth surfaces due to mechanical processes including abrasion, adhesion, surface fatigue, and corrosion. Unlike sudden failures from tooth breakage, gear wear is a gradual degradation that changes tooth profile geometry, increases backlash, Read more
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What is the Gyroscopic Effect in Rotor Dynamics?

Understanding the Gyroscopic Effect in Rotor Dynamics Definition: What is the Gyroscopic Effect? The gyroscopic effect is a physical phenomenon where a spinning rotor resists changes to its axis of rotation and generates moments (torques) when subjected to angular motion about an axis perpendicular to the spin axis. In rotor Read more
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What is a Hanning Window?

Understanding the Hanning Window Definition: What is a Hanning Window? The Hanning window is a specific type of mathematical function applied to a block of time waveform data before it is processed by a Fast Fourier Transform (FFT). It is one of the most commonly used windowing functions in vibration Read more
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What are Harmonics in Vibration Analysis?

Understanding Harmonics in Vibration Analysis Definition: What is a Harmonic? In vibration analysis, a harmonic is a frequency that is an integer multiple of a fundamental frequency. The fundamental frequency is typically the primary driving frequency of a system, such as the rotational speed of a shaft. This fundamental frequency Read more
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What is a High-Pass Filter? Frequency Selection Tool

Understanding High-Pass Filters Definition: What is a High-Pass Filter? High-pass filter (HPF) is a frequency-selective signal processing element that allows vibration components above a specified cutoff frequency to pass through while attenuating (reducing) components below the cutoff frequency. In vibration analysis, high-pass filters are used to remove low-frequency vibration (from Read more
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What is Holospectrum? Full Spectrum Analysis

Understanding Holospectrum Definition: What is Holospectrum? Holospectrum (also called full spectrum) is an advanced frequency analysis technique in rotor dynamics that processes simultaneous X and Y (horizontal and vertical) vibration measurements to separate shaft motion into forward precession components (orbiting in same direction as rotation) and backward precession components (orbiting Read more
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What is Hunting Tooth Frequency? Gear Pattern Repeat

Understanding Hunting Tooth Frequency Definition: What is Hunting Tooth Frequency? Hunting tooth frequency (HTF, also called assembly phase frequency or greatest common divisor frequency) is a low-frequency vibration component in gear pairs that represents the rate at which the same individual teeth on the pinion and gear come back into Read more
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What are Hydraulic Forces? Pump Vibration Sources

Understanding Hydraulic Forces in Pumps Definition: What are Hydraulic Forces? Hydraulic forces are forces exerted on pump components by the flowing liquid, including pressure-induced loads on impeller vanes, axial thrust from pressure differentials, radial forces from asymmetric pressure distributions, and pulsating forces from flow turbulence and vane-volute interaction. These forces Read more
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What is an IEPE Accelerometer? Integrated Electronics Sensor

Understanding IEPE Accelerometers Definition: What is an IEPE Accelerometer? IEPE accelerometer (Integrated Electronics Piezo-Electric, also called ICP®, voltage mode, or constant current accelerometer) is a piezoelectric accelerometer with built-in signal conditioning electronics powered by a constant current (typically 2-20 mA) supplied through the same two-wire cable that carries the output Read more
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What is Unbalance (Imbalance) in Machinery?

Understanding Unbalance (Imbalance) in Rotating Machinery Definition: What is Unbalance? Unbalance (often used interchangeably with imbalance) is a condition in a rotor where the center of mass (or center of gravity) is not aligned with the center of rotation. This offset, known as eccentricity, means that the mass is not Read more
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What is Impact Testing? Modal Analysis Technique

Understanding Impact Testing Definition: What is Impact Testing? Impact testing (also called impulse testing or impact modal analysis) is a modal testing technique using an instrumented impact hammer to apply broadband force impulses to structures while measuring the resulting vibration response with accelerometers. The technique calculates frequency response functions (FRFs) Read more
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What are Impeller Defects? Pump and Fan Damage

Understanding Impeller Defects Definition: What are Impeller Defects? Impeller defects are damage, wear, or deterioration in pump impellers and fan wheels, including vane erosion, corrosion, cracks, material buildup, broken vanes, and hub damage. These defects affect both mechanical balance (creating unbalance and vibration) and hydraulic/aerodynamic performance (reducing efficiency, flow, and Read more
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What is In-Situ Balancing? On-Site Rotor Correction

Understanding In-Situ Balancing Definition: What is In-Situ Balancing? In-situ balancing (from Latin “in situ,” meaning “in place”) is the practice of balancing a rotor while it remains installed in its machine, in its normal operating location, and under actual operating conditions. This is also commonly referred to as field balancing, Read more
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The Influence Coefficient Method in Rotor Balancing

The Influence Coefficient Method for Field Balancing Definition: What is an Influence Coefficient? An influence coefficient is a complex vector (containing both an amplitude and a phase angle) that describes how a rotor system responds to a known unbalance. Specifically, it represents the change in vibration at a specific measurement Read more
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What is Initial Unbalance in Rotor Balancing?

Understanding Initial Unbalance Definition: What is Initial Unbalance? Initial unbalance (also called original unbalance or as-found unbalance) is the unbalance condition that exists in a rotor before any balancing corrections have been applied. It represents the baseline state of the rotor and is measured during the first run of a Read more
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What is Integration in Vibration? Signal Conversion

Understanding Integration in Vibration Analysis Definition: What is Integration? Integration in vibration analysis is the mathematical process of converting vibration measurements from one parameter to another by performing integration in the time domain or dividing by frequency in the frequency domain. Most commonly, integration converts acceleration (measured by accelerometers) to Read more
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What is an Interference Diagram? Critical Speed Mapping

Understanding Interference Diagrams Definition: What is an Interference Diagram? An interference diagram is a graphical tool used in rotor dynamics to identify rotational speed ranges where excitation frequencies “interfere” with (match) the system’s natural frequencies, creating conditions for resonance. The term “interference” refers to the problematic interaction between an forcing Read more
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What is a Journal Bearing? Hydrodynamic Support

Understanding Journal Bearings Definition: What is a Journal Bearing? A journal bearing (also called a plain bearing, sleeve bearing, or fluid-film bearing) is a type of bearing that supports a rotating shaft through a thin film of pressurized lubricant rather than through rolling elements. The rotating shaft (the “journal”) is Read more
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What is a Keyphasor?

Understanding the Keyphasor Definition: What is a Keyphasor? A Keyphasor is the Bently Nevada trade name for a sensor that provides a once-per-revolution timing reference signal from a rotating shaft. While “Keyphasor” is a trademark, the term is often used generically in the industry to refer to any similar phase Read more
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What is Kurtosis in Vibration Analysis?

Kurtosis in Vibration Analysis for Fault Detection Definition: What is Kurtosis? Kurtosis is a statistical parameter that describes the shape of a probability distribution. In vibration analysis, it is applied to the time waveform signal to measure its “peakedness” or “impulsiveness.” A signal with high kurtosis is characterized by sharp, Read more
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What is a Laser Tachometer? Non-Contact Speed Measurement

Understanding Laser Tachometers Definition: What is a Laser Tachometer? Laser tachometer is a non-contact optical speed measurement device that uses a laser beam reflected from a rotating surface to measure rotational speed (RPM) and provide once-per-revolution timing pulses for phase reference in vibration analysis and balancing. Typically, reflective tape is Read more
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What is Laser Vibrometry? Non-Contact Optical Measurement

Understanding Laser Vibrometry Definition: What is Laser Vibrometry? Laser vibrometry is a non-contact optical technique for measuring vibration velocity and displacement using the Doppler shift of laser light reflected from vibrating surfaces. A laser Doppler vibrometer (LDV) directs a laser beam at the measurement point, and as the surface moves, Read more
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What is Lateral Vibration in Rotating Machinery?

Understanding Lateral Vibration in Rotating Machinery Definition: What is Lateral Vibration? Lateral vibration (also called radial vibration or transverse vibration) refers to the motion of a rotating shaft perpendicular to its axis of rotation. In simple terms, it is the side-to-side or up-and-down motion of the shaft as it spins. Read more
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What is Mechanical Looseness? Vibration Diagnosis

Understanding Mechanical Looseness in Rotating Machinery Definition: What is Mechanical Looseness? Mechanical looseness is a condition where components in rotating machinery have excessive clearances, inadequate fastening, worn fits, or structural deterioration that allows unintended relative motion between parts that should be rigidly connected. This creates non-linear vibration behavior characterized by Read more
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What is a Low-Pass Filter? Anti-Aliasing and Smoothing

Understanding Low-Pass Filters Definition: What is a Low-Pass Filter? Low-pass filter (LPF) is a frequency-selective signal processing element that allows vibration components below a specified cutoff frequency to pass through while attenuating (reducing or blocking) components above the cutoff frequency. In vibration analysis, low-pass filters serve critical functions including anti-aliasing Read more
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What is Machinery Protection? Equipment Safety Systems

Understanding Machinery Protection Systems Definition: What is Machinery Protection? Machinery protection (also called equipment protection or machine safeguarding) refers to monitoring and control systems that automatically detect dangerous operating conditions (vibration exceeding safe limits, excessive temperatures, abnormal pressures) and execute protective actions (alarms, shutdowns) to prevent catastrophic equipment damage, safety Read more
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What is Magnetic Pull? Unbalanced Magnetic Force in Motors

Understanding Magnetic Pull in Electric Motors Definition: What is Magnetic Pull? Magnetic pull (also called unbalanced magnetic pull or UMP) is a net radial electromagnetic force that develops in electric motors and generators when the air gap between the rotor and stator is not uniform. When the rotor is off-center Read more
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What is Mechanical Loosening? Progressive Deterioration

Understanding Mechanical Loosening Definition: What is Mechanical Loosening? Mechanical loosening is the progressive loss of clamping force, interference fit tension, or structural rigidity in properly assembled mechanical connections over time due to operating conditions, vibration, thermal cycling, material relaxation, or wear. Unlike initial looseness from improper assembly, mechanical loosening describes Read more
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What is Shaft Misalignment? Types, Causes, and Detection

Understanding Shaft Misalignment in Rotating Machinery Definition: What is Misalignment? Shaft misalignment is a condition where the rotational centerlines of two or more coupled shafts are not collinear when the machine is running under normal operating conditions. Along with unbalance, it is one of the most common causes of premature Read more
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What is Modal Analysis? (EMA, OMA)

Understanding Modal Analysis Definition: What is Modal Analysis? Modal analysis is the process of studying and characterizing the inherent dynamic properties of a structure or mechanical system. These properties—specifically its natural frequencies, damping ratios, and mode shapes—are known as the system’s “modal parameters.” Modal analysis determines the unique ways in Read more
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What is Modal Balancing? Advanced Flexible Rotor Technique

Understanding Modal Balancing Definition: What is Modal Balancing? Modal balancing is an advanced balancing technique specifically designed for flexible rotors that operates by targeting and correcting individual vibration modes rather than balancing at specific rotational speeds. The method recognizes that flexible rotors exhibit distinct mode shapes (patterns of deflection) at Read more
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What is Mode Shape in Rotor Dynamics?

Understanding Mode Shapes in Rotor Dynamics Definition: What is a Mode Shape? A mode shape (also called vibration mode or natural mode) is the characteristic spatial pattern of deformation that a rotor system assumes when vibrating at one of its natural frequencies. It describes the relative amplitude and phase of Read more
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What are Motor Defects? Electric Motor Diagnostics

Understanding Electric Motor Defects Definition: What are Motor Defects? Motor defects are faults and failures in electric motors including mechanical problems (bearing failures, rotor-to-stator contact, shaft issues), electromagnetic problems (broken rotor bars, stator winding failures, air gap irregularities), and combined electromechanical issues. These defects create characteristic vibration and electrical signatures Read more
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What is Mounting Resonance? Support System Dynamics

Understanding Mounting Resonance Definition: What is Mounting Resonance? Mounting resonance is a resonance condition where the mounting system—including vibration isolators, mounting rails, brackets, skids, or the complete equipment assembly on its supports—vibrates at one of its natural frequencies in response to excitation from the rotating machinery. This creates a situation Read more
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What is Sensor Mounting? Installation Methods

Understanding Sensor Mounting Definition: What is Sensor Mounting? Sensor mounting refers to the method and hardware used to attach vibration sensors (accelerometers, velocity sensors) to the measurement surface on machinery. The mounting method critically affects measurement quality, frequency response, and reliability. Proper mounting creates a rigid mechanical coupling that faithfully Read more
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What is Multi-Plane Balancing? Flexible Rotor Methods

Understanding Multi-Plane Balancing Definition: What is Multi-Plane Balancing? Multi-plane balancing is an advanced balancing procedure that uses three or more correction planes distributed along the length of a rotor to achieve acceptable vibration levels. This technique is necessary for flexible rotors—rotors that bend or flex significantly during operation because they Read more
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What is the N+2 Method in Multi-Plane Balancing?

Understanding the N+2 Method in Multi-Plane Balancing Definition: What is the N+2 Method? The N+2 method is an advanced balancing procedure used for multi-plane balancing of flexible rotors. The name describes the measurement strategy: if N is the number of correction planes required, the method uses N trial weight runs Read more
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What is Natural Frequency? (And Its Role in Resonance)

Understanding Natural Frequency Definition: What is a Natural Frequency? A natural frequency is the specific frequency at which an object or system will oscillate if it is disturbed from its resting position and then allowed to vibrate freely without any external forces. It is an inherent, fundamental property of the Read more
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What is a Nodal Point in Rotor Vibration?

Understanding Nodal Points in Rotor Vibration Definition: What is a Nodal Point? A nodal point (also called a node or nodal line when considering three-dimensional motion) is a specific location along a vibrating rotor where the displacement or deflection remains zero during vibration at a particular natural frequency. Even as Read more
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What is Non-Destructive Testing (NDT)?

Understanding Non-Destructive Testing (NDT) 1. Definition: What is Non-Destructive Testing? Non-Destructive Testing (NDT), also known as Non-Destructive Examination (NDE) or Non-Destructive Inspection (NDI), is a very broad group of analysis techniques used in science and industry to evaluate the properties of a material, component, or system without causing damage. The Read more
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What is a Notch Filter? Frequency Rejection Tool

Understanding Notch Filters Definition: What is a Notch Filter? Notch filter (also called band-stop filter, band-reject filter, or frequency trap) is a frequency-selective signal processing element that strongly attenuates vibration components within a narrow frequency band while allowing all frequencies outside that band to pass essentially unchanged. A notch filter Read more
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What is a Nyquist Plot in Vibration Analysis?

Understanding the Nyquist Plot (Polar Plot) Definition: What is a Nyquist Plot? A Nyquist plot, also commonly known as a polar plot in the field of vibration analysis, is a graph used to display the changing characteristics of a vibration vector on a polar coordinate system. Unlike a Bode plot, Read more
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What is Operating Deflection Shape (ODS) Analysis?

Understanding Operating Deflection Shape (ODS) Analysis Definition: What is an Operating Deflection Shape? Operating Deflection Shape (ODS) analysis is a technique used to visualize the actual vibration pattern of a machine and its support structure under its normal operating conditions. It involves measuring the vibration (amplitude and phase) at many Read more
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What is Oil Analysis (Tribology)? – Condition Monitoring

Understanding Oil Analysis (Tribology) 1. Definition: What is Oil Analysis? Oil Analysis (also known as Tribology) is a proactive maintenance and condition monitoring technique that involves the laboratory analysis of a lubricant’s properties, suspended contaminants, and wear debris. A small sample of oil is taken from a machine and sent Read more
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What is Oil Whirl in Vibration Analysis?

Understanding Oil Whirl Definition: What is Oil Whirl? Oil whirl is a type of self-excited, unstable vibration that occurs in machines equipped with fluid-film (journal) bearings, such as large turbines, compressors, and pumps. It is a form of fluid-induced instability where the oil film supporting the shaft begins to push Read more
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What is Online Monitoring? Continuous Condition Assessment

Understanding Online Monitoring Definition: What is Online Monitoring? Online monitoring (also called permanent monitoring, continuous monitoring, or installed systems) is a condition monitoring approach using permanently installed sensors and instruments that automatically collect vibration, temperature, and other data continuously or at frequent intervals (every few seconds to hours) without human Read more
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What is an Optical Tachometer? Light-Based Speed Sensor

Understanding Optical Tachometers Definition: What is an Optical Tachometer? Optical tachometer is a non-contact speed measurement device that uses light (visible LED, laser, or infrared) and a photodetector to sense rotation by detecting reflections from a rotating surface marked with reflective tape or by sensing interruptions of a light beam. Read more
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What is a Shaft Orbit in Vibration Analysis?

Understanding the Shaft Orbit Plot in Vibration Analysis Definition: What is a Shaft Orbit? A shaft orbit is a plot that shows the path of a rotating shaft’s geometric center during one or more revolutions. It is a two-dimensional view of the shaft’s motion within its bearing clearance, as if Read more
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What is Order Analysis in Vibration Monitoring?

Understanding Order Analysis for Variable-Speed Machines Definition: What is Order Analysis? Order analysis is a specialized vibration analysis technique used for machines that operate at varying speeds. Instead of plotting vibration amplitude against a fixed frequency axis (in Hz or CPM), it plots amplitude against “orders.” An order is a Read more
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What is an Overhung Rotor? Balancing Cantilever Designs

Understanding Overhung Rotors Definition: What is an Overhung Rotor? An overhung rotor (also called a cantilever rotor or cantilevered rotor) is a rotor configuration where the rotating mass extends outward beyond the supporting bearings, mounted in a cantilevered fashion. In this design, the rotor is supported on one side only, Read more
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What is Peak Amplitude in Vibration Analysis?

Understanding Peak Amplitude (Pk & Pk-Pk) 1. Definition: What is Peak Amplitude? Peak (Pk) Amplitude is a measure of the maximum amplitude of a vibration signal, measured from the zero or equilibrium position to the highest positive point of the waveform. In a simple, clean sinusoidal signal, this represents the Read more
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What is Peak Hold? Maximum Value Capture

Understanding Peak Hold Definition: What is Peak Hold? Peak hold is a measurement and display mode in vibration analyzers where the instrument continuously monitors the vibration signal and retains the maximum value (or maximum frequency component amplitudes) encountered during the measurement period. As new measurements are taken, the display is Read more
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Peak vs. Peak-to-Peak Vibration Measurement

Peak vs. Peak-to-Peak Amplitude in Vibration Analysis Definition: Distinguishing Peak and Peak-to-Peak Peak (Pk) and Peak-to-Peak (Pk-Pk) are two of the primary ways to quantify the amplitude, or magnitude, of a vibration signal. While closely related, they measure different aspects of the waveform and are used for different diagnostic purposes. Read more
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What is Pedestal Looseness? Structural Vibration

Understanding Pedestal Looseness Definition: What is Pedestal Looseness? Pedestal looseness is a mechanical condition where the bearing pedestal is inadequately secured to the baseplate or foundation, allowing unintended movement or rocking motion under dynamic loads. This looseness can result from loose anchor bolts, cracked pedestals, deteriorated grout, or degraded foundation Read more
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What is Periodic Monitoring? Route-Based Condition Assessment

Understanding Periodic Monitoring Definition: What is Periodic Monitoring? Periodic monitoring (also called route-based monitoring, scheduled monitoring, or interval monitoring) is a condition monitoring approach where trained technicians manually collect vibration and other condition data from equipment at regular intervals (weekly, monthly, quarterly) following predefined measurement routes. Using portable data collectors Read more
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What is Permanent Calibration in Rotor Balancing?

Understanding Permanent Calibration in Rotor Balancing Definition: What is Permanent Calibration? Permanent calibration (also called stored calibration or saved influence coefficients) is a technique in field balancing where the influence coefficients determined during an initial balancing procedure are saved and reused for subsequent balancing operations on the same machine or Read more
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What is Phase Angle? Timing Relationship in Vibration

Understanding Phase Angle in Vibration Definition: What is Phase Angle? Phase angle (often simply called phase) is the angular position, measured in degrees (0-360°), of the peak vibration relative to a once-per-revolution reference mark on the rotating shaft (from a tachometer or keyphasor). Alternatively, it can represent the timing relationship Read more
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What is Phase in Vibration Analysis?

Understanding Phase in Vibration Analysis Definition: What is Vibration Phase? Phase is a measurement that describes the timing relationship between two signals or, more commonly, the timing of a vibration signal relative to a specific reference point on a rotating shaft. It is a measure of “where” the vibration is Read more
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What is a Photoelectric Sensor? Optical Detection Device

Understanding Photoelectric Sensors Definition: What is a Photoelectric Sensor? Photoelectric sensor is an optical detection device that uses a light source (LED, laser, or infrared) and photodetector to sense the presence, absence, or position of objects or marks through light transmission, reflection, or interruption. In rotating machinery applications, photoelectric sensors Read more
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What is a Piezoelectric Accelerometer? Vibration Sensor

Understanding Piezoelectric Accelerometers Definition: What is a Piezoelectric Accelerometer? Piezoelectric accelerometer is a vibration sensor that uses the piezoelectric effect—where certain crystals generate electrical charge when mechanically stressed—to convert mechanical acceleration into an electrical signal proportional to vibration amplitude. When the sensor experiences acceleration, an internal mass (seismic mass) compresses Read more
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What is Pitting in Bearings and Gears? Surface Damage

Understanding Pitting in Bearings and Gears Definition: What is Pitting? Pitting is the formation of small cavities, craters, or depressions on the surface of bearing races, rolling elements, or gear teeth. Pitting can result from two distinct mechanisms: (1) fatigue pitting from rolling contact fatigue, representing early-stage surface fatigue damage, Read more
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What is a Polar Plot in Rotor Balancing?

Understanding Polar Plots in Rotor Balancing Definition: What is a Polar Plot? A polar plot (also called a polar diagram or Nyquist diagram in some contexts) is a circular graphical representation used in rotor balancing that displays vibration data as vectors. Each vector represents both the amplitude (magnitude) and phase Read more
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What is a Portable Analyzer? Field Vibration Instrument

Understanding Portable Vibration Analyzers Definition: What is a Portable Analyzer? Portable vibration analyzer (also called handheld analyzer or field analyzer) is a battery-powered, compact instrument providing comprehensive vibration analysis capabilities including FFT spectral analysis, time waveform display, envelope analysis, phase measurement, balancing calculations, and advanced diagnostics. Unlike data collectors optimized Read more
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What is Power Spectral Density? PSD Analysis

Understanding Power Spectral Density Definition: What is Power Spectral Density? Power spectral density (PSD) is a representation of vibration energy distribution across frequency, expressed as energy per unit frequency bandwidth (units: (m/s²)²/Hz for acceleration, (mm/s)²/Hz for velocity). Unlike a standard amplitude spectrum which shows amplitude at each frequency, PSD shows Read more
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What is Predictive Maintenance? Condition-Based Strategy

Understanding Predictive Maintenance Definition: What is Predictive Maintenance? Predictive maintenance (PdM) is a maintenance strategy that uses condition monitoring data to predict when equipment failures will occur and schedule maintenance at the optimal time—after a problem is detected but before functional failure happens. PdM combines periodic or continuous measurements (vibration, Read more
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What is Quasi-Static Unbalance?

Understanding Quasi-Static Unbalance 1. Definition: What is Quasi-Static Unbalance? Quasi-Static Unbalance is a specific and less common type of dynamic unbalance. It occurs when a rotor’s principal axis of inertia intersects the shaft’s rotational axis, but not at the rotor’s center of gravity. In simpler terms, it’s a condition that Read more
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What is Radial Vibration in Rotating Machinery?

Understanding Radial Vibration in Rotating Machinery Definition: What is Radial Vibration? Radial vibration is the motion of a rotating shaft perpendicular to its axis of rotation, extending outward from the center like radii of a circle. The term “radial” refers to any direction radiating from the shaft centerline, encompassing both Read more
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What is Recirculation? Low-Flow Pump Instability

Understanding Recirculation in Pumps Definition: What is Recirculation? Recirculation is a flow instability that occurs in centrifugal pumps and fans when operating at flow rates significantly below the design point (best efficiency point or BEP). At low flows, fluid partially reverses direction, flowing backward from the discharge region back toward Read more
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What is Reflective Tape? Tachometer Reference Marker

Understanding Reflective Tape Definition: What is Reflective Tape? Reflective tape (also called retro-reflective tape or tachometer tape) is a small piece of adhesive-backed material with highly reflective surface properties, applied to rotating shafts, couplings, or other rotating components to create a once-per-revolution reference mark detectable by optical or laser tachometers. Read more
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What is Remaining Useful Life (RUL)? Failure Prediction

Understanding Remaining Useful Life (RUL) Definition: What is Remaining Useful Life? Remaining useful life (RUL) is an estimate of the time period an equipment component or system can continue operating before reaching a defined failure threshold or requiring maintenance intervention. RUL is calculated from current condition indicators (vibration levels, trend Read more
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What is Residual Unbalance? – The Goal of Balancing

Understanding Residual Unbalance 1. Definition: What is Residual Unbalance? Residual Unbalance is the amount of unbalance that remains in a rotor after the balancing process has been completed. It is the unbalance that exists within the specified balancing tolerance. It’s important to understand that achieving perfect balance (zero unbalance) is Read more
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What is Resonance in Mechanical Systems?

Understanding Resonance in Mechanical Systems Definition: What is Resonance? Resonance is a physical phenomenon that occurs when a system is subjected to a periodic force at a frequency that matches one of its own natural frequencies. When this frequency matching occurs, the system begins to vibrate with extremely large amplitudes. Read more
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What is a Rigid Rotor in Balancing?

Understanding the Rigid Rotor 1. Definition: What is a Rigid Rotor? A Rigid Rotor is a rotor that does not significantly bend, flex, or change its shape under the influence of its own unbalance forces at its service operating speed. For balancing purposes, a rotor is considered to be rigid Read more
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What are Rolling Element Defects? Ball and Roller Damage

Understanding Rolling Element Defects Definition: What are Rolling Element Defects? Rolling element defects are damage, flaws, or imperfections in the balls or rollers of rolling element bearings. These defects include surface spalls, cracks, embedded contamination, material inclusions, and geometric imperfections. When a defective rolling element rotates through the bearing, it Read more
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What are Rotor Bar Defects? Broken Bars in Motors

Understanding Rotor Bar Defects Definition: What are Rotor Bar Defects? Rotor bar defects (also called broken rotor bars or cracked rotor bars) are fractures, cracks, or high-resistance connections in the conductor bars of squirrel cage induction motor rotors. Squirrel cage rotors consist of aluminum or copper bars embedded in iron Read more
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What is a Rotor-Bearing System? Integrated Dynamics

Understanding the Rotor-Bearing System Definition: What is a Rotor-Bearing System? A rotor-bearing system is the complete integrated mechanical assembly consisting of a rotating rotor (shaft with attached components), the supporting bearings that constrain its motion and carry loads, and the stationary support structure (bearing housings, pedestals, frame, and foundation) that Read more
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What is Rotor Dynamics? Theory and Applications

Understanding Rotor Dynamics Definition: What is Rotor Dynamics? Rotor dynamics is the specialized branch of mechanical engineering that studies the behavior and characteristics of rotating systems, particularly focusing on the vibration, stability, and response of rotors supported on bearings. This discipline combines principles from dynamics, mechanics of materials, control theory, Read more
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What is Rotor Eccentricity? Geometric Imbalance

Understanding Rotor Eccentricity Definition: What is Rotor Eccentricity? Rotor eccentricity (also called eccentricity or geometric runout) is a condition where the geometric center of a rotor or rotor component does not coincide with the axis of rotation (the centerline defined by the supporting bearings). This offset creates a situation where, Read more
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What is Rotor Instability? Self-Excited Vibration

Understanding Rotor Instability Definition: What is Rotor Instability? Rotor instability is a condition in rotating machinery where self-excited vibration develops and grows without bound (limited only by non-linear effects or system failure). Unlike vibration from unbalance or misalignment, which are forced vibrations responding to external forces, rotor instability is a Read more
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What is Rotor Rub? Contact Between Rotating and Stationary Parts

Understanding Rotor Rub in Rotating Machinery Definition: What is Rotor Rub? Rotor rub (also called rubbing or rotor-to-stator contact) is a condition where the rotating components of a machine make intermittent or continuous contact with stationary parts such as seals, bearing housings, or casing walls. This contact creates friction forces, Read more
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What is a Rotor in Mechanical Engineering?

Understanding the Rotor in Rotating Machinery Definition: What is a Rotor? A rotor is the primary rotating assembly within a piece of machinery. It typically consists of a central shaft upon which other components—such as impellers, blades, magnets, or armatures—are mounted. The entire assembly is supported by bearings and is Read more
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What is Route-Based Data Collection? – Predictive Maintenance

Understanding Route-Based Data Collection 1. Definition: What is Route-Based Data Collection? Route-Based Data Collection is the cornerstone of most predictive maintenance (PdM) and vibration monitoring programs. It is a systematic and periodic process where a technician uses a portable vibration analyzer or data collector to gather vibration data from a Read more
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What is Rubbing in Rotating Machinery? Friction Contact

Understanding Rubbing in Rotating Machinery Definition: What is Rubbing? Rubbing is the friction contact and relative sliding motion between rotating and stationary components in machinery. This term emphasizes the continuous friction aspect of rotor-to-stator contact, distinguishing it from light intermittent contact or impacts. Rubbing generates friction forces, produces significant heat Read more
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What is Shaft Runout? (Mechanical vs. Electrical)

Understanding Shaft Runout in Vibration Analysis Definition: What is Runout? Runout is a general term for imperfections in a rotor that produce a once-per-revolution (1x) signal, even when the rotor is turning at a very low speed where dynamic forces like unbalance are negligible. It is a measurement of the Read more
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What is Run-Up Analysis? Startup Vibration Testing

Understanding Run-Up Analysis Definition: What is Run-Up Analysis? Run-up analysis is the systematic measurement and evaluation of vibration amplitude and phase during equipment acceleration from rest or low speed to operating speed. Continuous data recording during startup enables identification of critical speeds (visible as peaks in amplitude), assessment of damping Read more
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What is Running Speed (1X) in Vibration Analysis?

Understanding Running Speed (1X) 1. Definition: What is Running Speed? Running Speed is the fundamental frequency in vibration analysis that corresponds to the rotational speed of a machine’s shaft. It is the frequency at which the shaft completes one full revolution. In vibration terminology, this frequency is almost always referred Read more
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What is Runup in Rotating Machinery Analysis?

Understanding Runup in Rotating Machinery Analysis Definition: What is Runup? Runup (also called startup or acceleration test) is the process of accelerating a rotating machine from rest (or low speed) to its normal operating speed while continuously monitoring vibration and other parameters. In rotor dynamics analysis, a runup test is Read more
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What are Seal Defects? Leakage and Friction Problems

Understanding Seal Defects in Rotating Machinery Definition: What are Seal Defects? Seal defects are damage, wear, or failures in sealing components that prevent lubricant leakage and exclude contaminants from rotating machinery. Common seal types include lip seals (radial shaft seals), mechanical face seals, labyrinth seals, and O-rings. Seal defects manifest Read more
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What is a Seismic Transducer? Inertial Reference Sensor

Understanding Seismic Transducers Definition: What is a Seismic Transducer? Seismic transducer (also called seismic sensor or inertial transducer) is a vibration sensor that uses an internal seismic mass (proof mass) suspended by springs or other compliant elements as an inertial reference to measure the absolute motion of the sensor base. Read more
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What is Self-Excited Vibration? – Unstable System Responses

Understanding Self-Excited Vibration 1. Definition: What is Self-Excited Vibration? Self-Excited Vibration (also known as a self-induced or unstable vibration) is a particularly dangerous type of vibration where the motion of a system induces the forces that, in turn, sustain or amplify that motion. This creates a feedback loop where the Read more
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What is Sensor Sensitivity? Output per Input Unit

Understanding Sensor Sensitivity Definition: What is Sensitivity? Sensitivity is the ratio of a sensor’s output signal to the input physical quantity being measured, representing the sensor’s gain or conversion factor. For vibration sensors, sensitivity defines how much electrical output (voltage or charge) is produced per unit of vibration (acceleration, velocity, Read more
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What is Shaft Bow? Causes, Detection, and Correction

Understanding Shaft Bow in Rotating Machinery Definition: What is Shaft Bow? Shaft bow (also called shaft bending, rotor bow, or simply “bow”) is a condition where a rotor shaft has developed a permanent or semi-permanent curvature, causing it to deviate from a straight centerline. Unlike temporary run-out that might be Read more
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