{"id":100283,"date":"2026-02-15T20:31:45","date_gmt":"2026-02-15T20:31:45","guid":{"rendered":"https:\/\/vibromera.eu\/?post_type=calculator&#038;p=100283"},"modified":"2026-02-15T20:31:45","modified_gmt":"2026-02-15T20:31:45","slug":"vibration-glossary","status":"publish","type":"calculator","link":"https:\/\/vibromera.eu\/bn\/calculators\/vibration-glossary\/","title":{"rendered":"Vibration Analysis Glossary | ISO 19499 | 100+ Terms"},"content":{"rendered":"\n<script type=\"application\/ld+json\">\n{\"@context\":\"https:\/\/schema.org\",\"@type\":\"WebApplication\",\"name\":\"Vibration Analysis Glossary\",\"description\":\"Interactive searchable glossary of 80+ vibration analysis terms with definitions, formulas, and related 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a:hover{text-decoration:underline}\n.vc-footer-links{margin-top:8px;font-size:12px}\n.vc-footer-links a{margin:0 8px}\n@media print{.vc-term-body{max-height:none!important}.vc-section-body{max-height:none!important}.vc-promo,.vc-search-bar,.vc-letter-nav{display:none!important}}\n<\/style>\n\n<div class=\"vc-calculator\" id=\"vc-vibration-glossary\">\n\n<header class=\"vc-header\">\n    <p class=\"vc-header-eyebrow\">Free Engineering Reference<\/p>\n    <h1 class=\"vc-header-title\">Vibration Analysis Glossary<\/h1>\n    <p class=\"vc-header-subtitle\">Interactive searchable glossary of vibration analysis terms with definitions, formulas, and cross-references. Based on ISO 19499 and industry standards.<\/p>\n    <div class=\"vc-badges\">\n        <span class=\"vc-badge\">ISO 19499<\/span>\n        <span class=\"vc-badge\">80+ Terms<\/span>\n        <span class=\"vc-badge\">Searchable<\/span>\n    <\/div>\n<\/header>\n\n<div class=\"vc-card\">\n    <div class=\"vc-search-bar\">\n        <input type=\"text\" class=\"vc-search-input\" id=\"vc-search\" placeholder=\"Search terms, abbreviations, or definitions...\" autocomplete=\"off\">\n        <div class=\"vc-search-info\" id=\"vc-search-info\">Showing all <span id=\"vc-term-count\">0<\/span> terms<\/div>\n    <\/div>\n    <div class=\"vc-letter-nav\" id=\"vc-letter-nav\"><\/div>\n    <div class=\"vc-glossary-list\" id=\"vc-glossary-list\"><\/div>\n<\/div>\n\n<!-- Related -->\n<div class=\"vc-section\" id=\"vc-sec-related\">\n    <button type=\"button\" class=\"vc-section-toggle\" aria-expanded=\"false\">\n        <span class=\"vc-section-toggle-text\">\n            <span class=\"vc-section-icon\">\ud83d\udd17<\/span>\n            <span class=\"vc-section-title\">Related Tools<\/span>\n        <\/span>\n        <svg class=\"vc-section-chevron\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><path d=\"M6 9l6 6 6-6\"\/><\/svg>\n    <\/button>\n    <div class=\"vc-section-body\">\n        <div class=\"vc-section-inner\">\n            <div class=\"vc-related\">\n                <a class=\"vc-related-link\" href=\"\/calculators\/diagnostic-matrix\/\">Vibration Diagnostic Matrix<\/a>\n                <a class=\"vc-related-link\" href=\"\/calculators\/residual-unbalance-iso1940\/\">Residual Unbalance<\/a>\n                <a class=\"vc-related-link\" href=\"\/calculators\/frequency-wavelength-calculator\/\">Frequency \u2194 Wavelength<\/a>\n                <a class=\"vc-related-link\" href=\"\/calculators\/speed-velocity-converter\/\">Speed Converter<\/a>\n            <\/div>\n        <\/div>\n    <\/div>\n<\/div>\n\n<div class=\"vc-promo\">\n    <div class=\"vc-promo-text\">\n        <strong>Vibromera \u2014 Portable Balancing &#038; Vibration Analysis<\/strong><br>\n        Professional field balancing instruments and software. Used in 50+ countries.\n    <\/div>\n    <a class=\"vc-promo-link\" href=\"https:\/\/vibromera.eu\/\" target=\"_blank\" rel=\"noopener\">Learn More<\/a>\n<\/div>\n\n<footer class=\"vc-footer\">\n    <p>\u00a9 2024\u20132025 <a href=\"https:\/\/vibromera.eu\/\">Vibromera<\/a> \u2014 Engineering Calculators<\/p>\n    <p style=\"font-size:12px;margin-top:4px;\">Based on ISO 19499 and industry standards. Last updated: February 2025<\/p>\n    <div class=\"vc-footer-links\">\n        <a href=\"\/calculators\/engineering-calculators\/\">All Calculators<\/a>\n        <a href=\"https:\/\/vibromera.eu\/contacts\/\">Contact<\/a>\n    <\/div>\n<\/footer>\n\n<\/div>\n\n<script>\n(function() {\n    'use strict';\n\n    var TERMS = [\n        {n:'Acceleration',abbr:'a',def:'Rate of change of velocity with respect to time. In vibration, measured in m\/s\u00b2, g, or mm\/s\u00b2. Acceleration emphasizes high-frequency components.',formula:'a = dv\/dt = d\u00b2x\/dt\u00b2',related:['Velocity','Displacement','g-value']},\n        {n:'Alignment',def:'The condition where the centerlines of coupled shafts are collinear within acceptable tolerances. Misalignment causes characteristic vibration at 1\u00d7, 2\u00d7, and 3\u00d7 RPM.',related:['Misalignment','Coupling']},\n        {n:'Amplitude',def:'The magnitude of a vibration signal. Can be expressed as peak, peak-to-peak, or RMS value. Amplitude indicates severity.',related:['Peak','Peak-to-Peak','RMS']},\n        {n:'Antifriction Bearing',abbr:'AFB',def:'A rolling element bearing (ball or roller) as opposed to a journal (sliding) bearing. Has characteristic defect frequencies (BPFI, BPFO, BSF, FTF).',related:['BPFI','BPFO','BSF','FTF']},\n        {n:'Axial',def:'Direction parallel to the shaft centerline. Axial vibration is significant for diagnosing misalignment, thrust bearing problems, and blade\/vane issues.',related:['Radial','Misalignment']},\n        {n:'Balancing',def:'The process of adjusting mass distribution on a rotor so that centrifugal forces are within acceptable limits. Can be single-plane (static) or two-plane (dynamic).',related:['Unbalance','ISO 21940','Trial Weight']},\n        {n:'Bandwidth',def:'The frequency range of a filter or measurement system. In spectrum analysis, bandwidth resolution determines the ability to distinguish closely spaced frequencies.',related:['FFT','Resolution','Spectrum']},\n        {n:'Baseline',def:'A reference vibration measurement taken when the machine is in known good condition. All subsequent measurements are compared against the baseline.',related:['Trend','Overall Level']},\n        {n:'Bearing Defect Frequency',def:'Characteristic frequency generated by a defect on a specific bearing component. Four main types: BPFI (inner race), BPFO (outer race), BSF (ball\/roller), FTF (cage).',related:['BPFI','BPFO','BSF','FTF']},\n        {n:'BPFI',abbr:'Ball Pass Frequency Inner',def:'Frequency at which rolling elements pass over a defect on the inner race. Typically the highest of the four bearing frequencies. Modulated by shaft speed.',formula:'BPFI = (N\/2) \u00d7 (1 + Bd\/Pd \u00d7 cos(\u03b1)) \u00d7 RPM\/60',related:['BPFO','BSF','FTF','Bearing Defect Frequency']},\n        {n:'BPFO',abbr:'Ball Pass Frequency Outer',def:'Frequency at which rolling elements pass over a defect on the outer race. Most common bearing defect frequency because the outer race is typically the loaded zone.',formula:'BPFO = (N\/2) \u00d7 (1 \u2212 Bd\/Pd \u00d7 cos(\u03b1)) \u00d7 RPM\/60',related:['BPFI','BSF','FTF','Bearing Defect Frequency']},\n        {n:'BSF',abbr:'Ball Spin Frequency',def:'Rotational frequency of a rolling element (ball or roller) spinning on its own axis. Defects on rolling elements appear at 2\u00d7 BSF due to the defect contacting both races per revolution.',formula:'BSF = (Pd\/(2\u00d7Bd)) \u00d7 (1 \u2212 (Bd\/Pd \u00d7 cos(\u03b1))\u00b2) \u00d7 RPM\/60',related:['BPFI','BPFO','FTF']},\n        {n:'Broadband',def:'Vibration energy spread across a wide frequency range rather than concentrated at discrete frequencies. Indicates turbulence, cavitation, or advanced bearing wear.',related:['Narrowband','Spectrum']},\n        {n:'Campbell Diagram',def:'A plot showing natural frequencies vs. operating speed, used to identify potential resonance conditions. Critical for variable-speed machinery.',related:['Critical Speed','Natural Frequency','Resonance']},\n        {n:'Cavitation',def:'Formation and collapse of vapor bubbles in a fluid (pump). Produces broadband high-frequency vibration and distinctive crackling noise. Damages impeller vanes.',related:['Broadband','Pump']},\n        {n:'CPM',abbr:'Cycles Per Minute',def:'Frequency unit commonly used in vibration analysis. 1 CPM = 1\/60 Hz. Machine speed in RPM directly equals the 1\u00d7 frequency in CPM.',formula:'CPM = Hz \u00d7 60',related:['Hz','Orders']},\n        {n:'Crest Factor',def:'Ratio of peak value to RMS value of a vibration signal. Normal value is ~1.414 for a sine wave. High crest factor (>3.5) indicates impulsive events like bearing impacts.',formula:'CF = Peak \/ RMS',related:['Peak','RMS','Kurtosis']},\n        {n:'Critical Speed',def:'Rotational speed at which a rotor system\\'s natural frequency coincides with the excitation frequency (usually 1\u00d7 RPM), causing resonance and high vibration amplitudes.',related:['Natural Frequency','Resonance','Campbell Diagram']},\n        {n:'Damping',def:'The mechanism by which vibrational energy is dissipated as heat. Affects resonance amplitude and decay rate. Measured by damping ratio (\u03b6) or logarithmic decrement.',formula:'\u03b6 = c \/ (2\u221a(km))',related:['Resonance','Logarithmic Decrement','Transmissibility']},\n        {n:'Displacement',def:'The distance a vibrating object moves from its rest position. Measured in \u03bcm (microns) or mils (1 mil = 25.4 \u03bcm). Emphasizes low-frequency vibration.',formula:'x(t) = X sin(\u03c9t + \u03c6)',related:['Velocity','Acceleration','Proximity Probe']},\n        {n:'Eccentricity',def:'The offset of the center of mass from the geometric center of a rotor. Causes unbalance forces proportional to the square of rotational speed.',formula:'e = U \/ m [\u03bcm]',related:['Unbalance','Runout']},\n        {n:'Envelope Analysis',def:'A demodulation technique that extracts the amplitude modulation from a high-frequency carrier signal. Essential for early detection of rolling element bearing defects.',related:['BPFI','BPFO','Demodulation','High-Frequency']},\n        {n:'FFT',abbr:'Fast Fourier Transform',def:'Mathematical algorithm that converts a time-domain signal into its frequency-domain spectrum. The fundamental tool of vibration analysis. Shows amplitude vs. frequency.',related:['Spectrum','Frequency','Time Waveform']},\n        {n:'Frequency',abbr:'f',def:'The number of complete cycles per unit time. Measured in Hz (cycles\/second) or CPM (cycles\/minute). In vibration, relates to the source of excitation.',formula:'f = 1\/T [Hz]',related:['Hz','CPM','Orders','Period']},\n        {n:'FTF',abbr:'Fundamental Train Frequency',def:'The rotational frequency of the bearing cage (retainer). Typically 0.35\u20130.45\u00d7 shaft speed. Cage defects are relatively rare but cause amplitude modulation.',formula:'FTF = (1\/2) \u00d7 (1 \u2212 Bd\/Pd \u00d7 cos(\u03b1)) \u00d7 RPM\/60',related:['BPFI','BPFO','BSF']},\n        {n:'g-value',def:'Acceleration expressed in units of gravitational acceleration. 1g = 9.80665 m\/s\u00b2. Common in vibration measurement, especially for high-frequency analysis.',formula:'1g = 9.80665 m\/s\u00b2',related:['Acceleration','m\/s\u00b2']},\n        {n:'Harmonic',def:'A vibration component at an integer multiple of a fundamental frequency. 2\u00d7 is the second harmonic, 3\u00d7 is the third, etc. Harmonics indicate nonlinear behavior (looseness, misalignment).',related:['Subharmonic','Orders','Fundamental']},\n        {n:'Hz',abbr:'Hertz',def:'SI unit of frequency. One hertz equals one cycle per second. Named after Heinrich Hertz. In vibration: 1 Hz = 60 CPM.',formula:'1 Hz = 1 cycle\/second = 60 CPM',related:['Frequency','CPM']},\n        {n:'Imbalance',def:'See Unbalance. The terms are often used interchangeably in practice, though \"unbalance\" is the preferred ISO terminology.',related:['Unbalance','Balancing','Eccentricity']},\n        {n:'ISO 10816',def:'International standard for evaluating machine vibration by measurements on non-rotating parts (bearing housings). Superseded by ISO 20816 series but still widely referenced.',related:['ISO 20816','Vibration Severity','Overall Level']},\n        {n:'ISO 20816',def:'Current standard series for measurement and evaluation of machine vibration. Replaced ISO 10816. Specifies vibration limits for various machine types based on broadband velocity RMS.',related:['ISO 10816','Vibration Severity']},\n        {n:'ISO 21940',def:'International standard series for rotor balancing. Part 11 (formerly ISO 1940-1) defines balance quality grades G0.4 to G4000 and permissible residual unbalance.',related:['Balancing','Unbalance','Balance Grade']},\n        {n:'Jerk',def:'Rate of change of acceleration with respect to time (third derivative of displacement). Units: m\/s\u00b3. Occasionally used in ride comfort and shock analysis.',formula:'j = da\/dt = d\u00b3x\/dt\u00b3',related:['Acceleration','Velocity']},\n        {n:'Journal Bearing',def:'A sliding contact (plain) bearing where the shaft rotates within a lubricated bore. Exhibits oil whirl and oil whip instabilities at certain conditions.',related:['Oil Whirl','Oil Whip','Bearing']},\n        {n:'Kurtosis',def:'Statistical measure of the \"peakedness\" of a probability distribution. Normal vibration: kurtosis \u2248 3. High kurtosis (>4) indicates impulsive events (bearing defects, gear impacts).',related:['Crest Factor','Statistics']},\n        {n:'Logarithmic Decrement',abbr:'\u03b4',def:'The natural logarithm of the ratio of successive amplitudes in a freely decaying vibration. Used to determine the damping ratio of a system.',formula:'\u03b4 = ln(Xn\/Xn+1) = 2\u03c0\u03b6\/\u221a(1\u2212\u03b6\u00b2)',related:['Damping','Natural Frequency']},\n        {n:'Looseness',def:'Mechanical looseness in a machine causes truncated or clipped waveforms, producing many harmonics (floor of harmonics) in the spectrum. Types: structural, rotating, bearing.',related:['Harmonic','Subharmonic']},\n        {n:'Misalignment',def:'Offset or angular deviation between coupled shaft centerlines. Angular misalignment produces high axial vibration at 1\u00d7 and 2\u00d7. Offset produces high radial vibration at 2\u00d7.',related:['Alignment','Coupling','Axial']},\n        {n:'Natural Frequency',abbr:'fn',def:'The frequency at which a system vibrates freely after being disturbed. Determined by mass and stiffness. Resonance occurs when excitation frequency equals natural frequency.',formula:'fn = (1\/2\u03c0) \u00d7 \u221a(k\/m)',related:['Resonance','Critical Speed','Damping']},\n        {n:'Octave',def:'A frequency ratio of 2:1. One octave above 100 Hz is 200 Hz. 1\/3 octave bands are commonly used in acoustic analysis. Used for broadband vibration specifications.',related:['Frequency','Bandwidth']},\n        {n:'Oil Whirl',def:'A sub-synchronous vibration in journal bearings, typically at 0.42\u20130.48\u00d7 shaft speed. Caused by hydrodynamic instability in the oil film. Can progress to oil whip at 2\u00d7 critical speed.',related:['Oil Whip','Journal Bearing','Subharmonic']},\n        {n:'Oil Whip',def:'A severe sub-synchronous vibration in journal bearings locked at the first rotor critical speed, regardless of running speed. Develops from oil whirl when speed exceeds 2\u00d7 critical.',related:['Oil Whirl','Journal Bearing','Critical Speed']},\n        {n:'Orbit',def:'A 2D plot of shaft centerline motion within a bearing, created from two orthogonal proximity probes (typically X-Y at 90\u00b0). Shape indicates the type of fault.',related:['Proximity Probe','Shaft Centerline']},\n        {n:'Orders',def:'Multiples of the shaft rotational frequency. 1\u00d7 = 1st order = shaft speed. 2\u00d7 = 2nd order = twice shaft speed. Orders are independent of actual RPM.',related:['Harmonic','Frequency','RPM']},\n        {n:'Overall Level',def:'The broadband vibration amplitude, typically measured as RMS velocity (mm\/s or in\/s) over a defined frequency range (e.g., 10\u20131000 Hz per ISO 10816).',related:['RMS','ISO 10816','Trend']},\n        {n:'Peak',abbr:'Pk',def:'The maximum positive or negative amplitude of a vibration signal. Peak = \u221a2 \u00d7 RMS for a pure sine wave. Used for displacement and acceleration measurements.',formula:'Peak = \u221a2 \u00d7 RMS (for sine wave)',related:['RMS','Peak-to-Peak','Amplitude']},\n        {n:'Peak-to-Peak',abbr:'Pk-Pk',def:'The total swing from maximum negative to maximum positive amplitude. Peak-to-Peak = 2 \u00d7 Peak for a symmetric waveform. Standard for displacement measurements.',formula:'Pk-Pk = 2 \u00d7 Peak (symmetric)',related:['Peak','RMS','Displacement']},\n        {n:'Phase',abbr:'\u03c6',def:'The angular relationship between the vibration signal and a reference point (keyphasor). Phase indicates the \"heavy spot\" position for balancing and helps diagnose fault types.',related:['Balancing','Keyphasor','Unbalance']},\n        {n:'Proximity Probe',def:'A non-contact eddy current sensor that measures shaft displacement relative to the bearing housing. Standard: API 670. Typical sensitivity: 7.87 mV\/\u03bcm (200 mV\/mil).',related:['Displacement','Orbit','Runout']},\n        {n:'Radial',def:'Direction perpendicular to the shaft centerline. Radial vibration is measured horizontally (H) and vertically (V) on bearing housings.',related:['Axial','Horizontal','Vertical']},\n        {n:'Resonance',def:'Condition where excitation frequency equals a natural frequency, causing greatly amplified vibration. Amplitude amplification depends on damping. Can be catastrophic if damping is low.',related:['Natural Frequency','Critical Speed','Damping']},\n        {n:'RMS',abbr:'Root Mean Square',def:'The square root of the average of squared values over one cycle. For a sine wave, RMS = 0.707 \u00d7 Peak. RMS represents the energy content of the signal. Standard for velocity measurements.',formula:'RMS = \u221a(1\/T \u00d7 \u222bx\u00b2dt) = 0.707 \u00d7 Peak (sine)',related:['Peak','Peak-to-Peak','Overall Level']},\n        {n:'Rotor',def:'The rotating component of a machine. In vibration analysis, the rotor mass, stiffness, and balance condition determine the vibration characteristics.',related:['Balancing','Unbalance','Critical Speed']},\n        {n:'RPM',abbr:'Revolutions Per Minute',def:'Rotational speed of a shaft. The fundamental frequency (1\u00d7) in vibration analysis. RPM\/60 = Hz.',formula:'f\u2081\u2093 = RPM \/ 60 [Hz]',related:['Frequency','Orders','CPM']},\n        {n:'Runout',def:'Total indicated reading (TIR) of a shaft surface measured with a dial indicator or proximity probe. Includes mechanical and electrical runout. Must be subtracted from vibration readings.',related:['Eccentricity','Proximity Probe','Displacement']},\n        {n:'Shaft',def:'The rotating element that transmits torque and supports the rotor. Shaft condition (straightness, surface finish, cracks) directly affects vibration behavior.',related:['Rotor','Runout','Critical Speed']},\n        {n:'Sideband',def:'Frequency components appearing on either side of a main peak, separated by a modulating frequency. Common around gear mesh frequency (modulated by shaft speed) and bearing defect frequencies.',related:['Modulation','Gear Mesh','Bearing Defect Frequency']},\n        {n:'Spectrum',def:'A plot of vibration amplitude versus frequency, obtained through FFT analysis. The primary diagnostic tool in vibration analysis. Shows which frequencies contain the most energy.',related:['FFT','Frequency','Amplitude']},\n        {n:'Subharmonic',def:'A vibration component at a fraction of a fundamental frequency (e.g., 0.5\u00d7, 0.33\u00d7). Subharmonics indicate looseness, oil whirl, belt problems, or rub conditions.',related:['Harmonic','Oil Whirl','Looseness']},\n        {n:'Synchronous',def:'Vibration that occurs at exactly the shaft rotational frequency (1\u00d7) or its exact multiples. Synchronous vibration is \"locked\" to shaft speed.',related:['Orders','Non-synchronous','RPM']},\n        {n:'Time Waveform',def:'The vibration signal displayed as amplitude versus time. Shows the actual motion pattern. Essential for diagnosing impacts, truncation, modulation, and transient events.',related:['FFT','Spectrum','Waveform']},\n        {n:'Transmissibility',def:'The ratio of vibration amplitude transmitted through a support\/isolator to the input amplitude. At resonance, T >> 1. Above \u221a2 \u00d7 fn, isolation begins (T < 1).',formula:'T = 1 \/ \u221a((1\u2212r\u00b2)\u00b2 + (2\u03b6r)\u00b2), r = f\/fn',related:['Resonance','Damping','Isolation']},\n        {n:'Trend',def:'The historical record of vibration measurements over time. Trending is the most powerful predictive maintenance tool \u2014 identifies degradation long before failure.',related:['Baseline','Overall Level','Condition Monitoring']},\n        {n:'Unbalance',def:'Condition where the mass center of a rotor does not coincide with its rotation axis. The most common cause of vibration in rotating machinery. Produces 1\u00d7 vibration proportional to speed\u00b2.',formula:'F = m \u00d7 e \u00d7 \u03c9\u00b2',related:['Balancing','Eccentricity','ISO 21940']},\n        {n:'Velocity',abbr:'v',def:'Rate of change of displacement with respect to time. Measured in mm\/s (metric) or in\/s (imperial). Velocity RMS is the primary parameter for evaluating vibration severity per ISO standards.',formula:'v = dx\/dt',related:['Displacement','Acceleration','RMS','ISO 10816']},\n        {n:'Vibration',def:'Oscillatory motion of a mechanical system about an equilibrium position. Characterized by frequency (Hz), amplitude (displacement, velocity, or acceleration), and phase.',related:['Frequency','Amplitude','Phase']},\n        {n:'Vibration Severity',def:'Overall vibration level used to assess machine condition. Typically measured as broadband velocity RMS per ISO 10816 \/ ISO 20816. Classified into zones: A (new), B (acceptable), C (alert), D (danger).',related:['ISO 10816','ISO 20816','Overall Level']},\n        {n:'Waterfall Plot',def:'A 3D display showing multiple spectra stacked over time or speed. Excellent for visualizing changes during run-up\/coast-down, identifying resonances, and tracking fault progression.',related:['Spectrum','Campbell Diagram','Trend']},\n        {n:'Wavelength',abbr:'\u03bb',def:'The spatial distance between two successive points in phase on a wave. In vibration: \u03bb = wave speed \/ frequency. Important for sensor placement and mode shape analysis.',formula:'\u03bb = v \/ f',related:['Frequency','Wave Speed']},\n        {n:'Whirl',def:'Orbital motion of a shaft within a bearing clearance. Forward whirl rotates in the same direction as shaft rotation. Backward whirl is opposite. Related to bearing stability.',related:['Oil Whirl','Orbit','Journal Bearing']},\n        {n:'Window Function',def:'A mathematical function applied to time-domain data before FFT to reduce spectral leakage. Common types: Hanning (general), Flat-top (amplitude accuracy), Rectangular (transients).',related:['FFT','Spectrum','Leakage']},\n        {n:'Zero-to-Peak',def:'Same as Peak. The maximum amplitude measured from the zero (mean) line to the extreme of the waveform.',related:['Peak','Peak-to-Peak','RMS']},\n        {n:'1\u00d7 (First Order)',def:'Vibration at exactly the shaft rotational frequency. The most common vibration component. Primary indicator of unbalance, but also affected by misalignment, bowed shaft, and eccentricity.',related:['Orders','Unbalance','RPM']},\n        {n:'2\u00d7 (Second Order)',def:'Vibration at twice the shaft speed. Key indicator of misalignment and looseness. Also caused by ovality, belt drives (2-pole), and cracked shafts.',related:['Orders','Misalignment','Looseness']},\n        {n:'Accelerometer',def:'A sensor that measures vibration acceleration. Types: piezoelectric (most common), MEMS, piezoresistive. Covers wide frequency range (0.5 Hz to 20+ kHz). Output in mV\/g.',related:['Acceleration','Sensor','Piezoelectric']},\n        {n:'Condition Monitoring',def:'The process of monitoring machine parameters (vibration, temperature, oil analysis) to detect developing faults and plan maintenance. Part of predictive maintenance strategy.',related:['Trend','Baseline','Predictive Maintenance']},\n        {n:'Coupling',def:'Mechanical connection between two shafts. Types: rigid, flexible, gear, disc. Each type transmits different vibration characteristics and has different alignment tolerances.',related:['Alignment','Misalignment']},\n        {n:'Demodulation',def:'Signal processing technique to extract the modulating signal (envelope) from a modulated carrier. Used in envelope analysis for bearing defect detection. Also called amplitude demodulation.',related:['Envelope Analysis','BPFI','BPFO']},\n        {n:'Gear Mesh Frequency',abbr:'GMF',def:'The fundamental frequency at which gear teeth engage. GMF = number of teeth \u00d7 shaft RPM \/ 60. Sidebands around GMF indicate gear wear, eccentricity, or tooth damage.',formula:'GMF = Z \u00d7 RPM \/ 60',related:['Sideband','Harmonic']},\n        {n:'High-Frequency Detection',abbr:'HFD',def:'Measurement of vibration energy in the high-frequency range (typically 5\u201360 kHz). Used for early bearing defect detection before defects appear in the normal spectrum.',related:['Envelope Analysis','Bearing Defect Frequency','Ultrasonic']},\n        {n:'Impact Test',def:'A technique to determine natural frequencies by striking a structure with an instrumented hammer and measuring the response. Also called bump test or modal test.',related:['Natural Frequency','Modal Analysis','Resonance']},\n        {n:'Keyphasor',def:'A once-per-revolution reference signal from a shaft notch or key. Provides phase reference and exact speed measurement. Essential for balancing and order tracking.',related:['Phase','Tachometer','Balancing']},\n        {n:'Modal Analysis',def:'The study of a structure\\'s dynamic properties: natural frequencies, mode shapes, and damping. Can be experimental (impact testing) or analytical (FEA).',related:['Natural Frequency','Impact Test','Mode Shape']},\n        {n:'Orbit Plot',def:'See Orbit. A 2D representation of shaft centerline motion within a bearing, typically from two proximity probes at 90\u00b0.',related:['Orbit','Proximity Probe']},\n        {n:'Vane Pass Frequency',abbr:'VPF',def:'In centrifugal pumps and fans, the frequency at which impeller vanes pass a stationary component (volute cutwater). VPF = number of vanes \u00d7 RPM \/ 60.',formula:'VPF = Z \u00d7 RPM \/ 60',related:['Blade Pass','Pump','Fan']},\n        {n:'Blade Pass Frequency',abbr:'BPF',def:'Frequency at which fan or turbine blades pass a fixed point. BPF = number of blades \u00d7 RPM \/ 60. High BPF amplitude indicates uneven blade spacing, resonance, or obstruction.',formula:'BPF = Z \u00d7 RPM \/ 60',related:['Vane Pass Frequency','Fan']},\n        {n:'Torsional Vibration',def:'Oscillatory angular motion (twisting) of a shaft. Not detectable by standard accelerometers or proximity probes. Requires special sensors (encoders, laser, strain gauges).',related:['Shaft','Coupling','Damping']}\n    ];\n\n    \/\/ Sort alphabetically\n    TERMS.sort(function(a, b) { return a.n.localeCompare(b.n); });\n\n    function $(id) { return document.getElementById(id); }\n\n    function renderTerms(filter, letterFilter) {\n        var list = $('vc-glossary-list');\n        var html = '';\n        var count = 0;\n        var fl = (filter || '').toLowerCase();\n\n        TERMS.forEach(function(t, i) {\n            var searchText = (t.n + ' ' + (t.abbr || '') + ' ' + t.def + ' ' + (t.related || []).join(' ')).toLowerCase();\n            var firstLetter = t.n.charAt(0).toUpperCase();\n            if (firstLetter >= '0' && firstLetter <= '9') firstLetter = '#';\n\n            if (fl && searchText.indexOf(fl) === -1) return;\n            if (letterFilter && firstLetter !== letterFilter) return;\n\n            count++;\n            html += '<div class=\"vc-term\" data-idx=\"' + i + '\">';\n            html += '<button type=\"button\" class=\"vc-term-header\"><span><span class=\"vc-term-name\">' + t.n + '<\/span>';\n            if (t.abbr) html += '<span class=\"vc-term-abbr\">' + t.abbr + '<\/span>';\n            html += '<\/span><svg class=\"vc-term-chevron\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><path d=\"M6 9l6 6 6-6\"\/><\/svg><\/button>';\n            html += '<div class=\"vc-term-body\"><div class=\"vc-term-inner\">';\n            html += '<p class=\"vc-term-def\">' + t.def + '<\/p>';\n            if (t.formula) html += '<div class=\"vc-term-formula\">' + t.formula + '<\/div>';\n            if (t.related && t.related.length) {\n                html += '<div class=\"vc-term-related\">Related: ';\n                html += t.related.map(function(r) { return '<a data-search=\"' + r + '\">' + r + '<\/a>'; }).join(', ');\n                html += '<\/div>';\n            }\n            html += '<\/div><\/div><\/div>';\n        });\n\n        if (count === 0) {\n            html = '<div class=\"vc-no-results\">No terms found matching \"' + (filter || letterFilter || '') + '\"<\/div>';\n        }\n\n        list.innerHTML = html;\n        $('vc-term-count').textContent = count;\n\n        \/\/ Click handlers for terms\n        list.querySelectorAll('.vc-term-header').forEach(function(btn) {\n            btn.addEventListener('click', function() {\n                this.closest('.vc-term').classList.toggle('vc-open');\n            });\n        });\n\n        \/\/ Related term links\n        list.querySelectorAll('.vc-term-related a').forEach(function(link) {\n            link.addEventListener('click', function() {\n                var q = this.getAttribute('data-search');\n                $('vc-search').value = q;\n                currentLetter = null;\n                renderLetterNav();\n                renderTerms(q, null);\n            });\n        });\n    }\n\n    \/\/ Letter navigation\n    var currentLetter = null;\n    function renderLetterNav() {\n        var nav = $('vc-letter-nav');\n        var letters = {};\n        TERMS.forEach(function(t) {\n            var l = t.n.charAt(0).toUpperCase();\n            if (l >= '0' && l <= '9') l = '#';\n            letters[l] = true;\n        });\n\n        var allLetters = '#ABCDEFGHIJKLMNOPQRSTUVWXYZ'.split('');\n        var html = '<button type=\"button\" class=\"vc-letter-btn' + (!currentLetter ? 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