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 موضوع: كتاب The Vibration Analysis Handbook الثلاثاء 31 يناير 2012, 1:45 am  

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TABLE OF CONTENTS CHAPTER ONE: INTRODUCTION TO MACHINERY VIBRATION TheoryofVibration . 1 HarmonicMotion . 1 Periodic Motion 1 RandomMotion 3 The Relationship between Time and Frequency 3 Time . 3 Frequency . 4 Amplitude Measurement . 6 Sources of Frequencies . 8 Generated Frequencies . 8 Excited Frequencies . 9 Frequencies Caused by Electronic Phenomena 17 ForcingFunction . 20 Combinations of Machine Problems 21 Mixing Frequencies . 22 Electrical and Mechanical Relationship 23 Time and Frequency Domain . 24 Relationship between Velocity. Displacement. and Acceleration . 25 Units of Measurement . 27 Relationships . 27 Ways of Measuring Vibration . 32 Relation between Diameter. Speed. and RPM . 32 How To Determine Machine Speed in FPM from the Vibration Data . 33 Conclusion and Efficiencies . 34 CHAPTER TWO: TIME AND FREQUENCY ANALYSIS TECHNIQUES Introduction 35 Basicphysics 35 Single Frequency . 36 Single Frequency with Harmonics 41 Clipping .52 SquareWave 52 Natural Frequencies 55 Multiple Frequencies.Linear Systems 55 High Frequency Riding a Low Frequency 55 Multiple Frequencies.Nonlinear Systems . 56 AmplitudeModulation 57 Sum and Difference Frequencies .61 Pulses .65 FrequencyModulation 67 Conclusion .68CHAPTER THREE: HARDWARE AND SOFTWARE REQUIRED FOR ACCURATE DIAGNOSTICS Hardware 71 Introduction 71 Personal Computer . 72 Realtime Analyzer . 73 Datacollection 76 Printers 78 Transducers 78 Displacement Transducers . 79 Velocity Transducers 81 Accelerometers 82 Pressure Transducers . 83 Microphones 83 OncePerRevolution Markers . 84 Multiplexer . 85 Gauss Meter 87 Software . 87 Introduction 87 Group 1. Toolbox Software . 90 Signal Analysis Program . 90 Vibration Calculation Program 90 Resonance and Deflection Calculator (RADC) . 92 Bearing Calculation Program . 92 Gears Program 95 Roll Ratio Program and Rusch Chart . 97 Group 2. Machine Doctor (MACHDOC) . 98 MACHDOC 98 Polar Plot . 100 Time Plot . 102 Balancing . 102 Diagnostic Database . 103 Diagnostic Modules . 108 Roll Quality Assurance Program . 109 Group3 110 Group4 110 CHAPTER FOUR: ACCURATE EVALUATION OF MACHINERY CONDITION Introduction .111 Theory .111 Calibration 115 Frequencies Generated . 116 Datacollection .117 Transducer Selection .118 Continuous Monitoring . 118 CommonProblems 119Imbalance 119 Bentshaft 119 SoftFoot . 122 Misalignment . 122 Looseness 125 Bearings Loose on the Shaft 125 Bearings Loose in the Housing 126 Common Forms of Looseness . 128 Noise . 128 Diagnosis of Looseness 129 Resonance 129 Rubs 130 Problems That Cause Pulses 130 OilWhirl 134 Analysis of Electric Motors . 135 Motors OutofMagnetic Center . 136 Broken Rotor Bars . 139 TurnToTurn Shorts in Windings 143 Vibration Problems in Synchronous Motors 144 SirenEffect . 146 Solo Data on Motors 146 Steam Turbines 148 Pumps 150 Impeller Contact .150 Starvation 151 Cavitation 152 Compressors 152 Fans 154 Special Tests 155 Startup/Coast Down Data . 155 Bump Tests .158 Noise Recording .160 Synchronous Time Averaging (STA) 161 Relative Motion Measurements (RMM) 164 CHAPTER FIVE: ACCURATE DIAGNOSIS OF ANTIFRICTION BEARINGS Introduction 167 Datacollection 167 Transducer Selection 167 Generated Frequencies 167 Fundamental Train Frequency 168 Ball Pass Frequency of Outer Race .169 Ball Pass Frequency of Inner Race .170 Ball Spin Frequency 170 Application of the Bearing Formulas .172 Outer Race Analysis 175 Inner Race Analysis 176 Ball Spin Frequency Analysis .176 Fundamental Train Frequency Analysis . 177VCI Bearing Calculation Program 177 Bearing Defects . 178 Raceways . 178 Outer Race 178 InnerRace . 181 Outer and Inner Race Amplitude . 185 Modulation of Ball Pass Frequency 185 Rolling Elements. Balls. and Rollers . 186 Cage . 189 Multiple Defects 189 Progressive Bearing Failure 193 Defectseverity . 196 Bearing Behavior 196 Inner Race Defect Length . 197 Defect Length Calculation . 201 Deep Fatigue Spalls vs.Shallow Flaking 203 Problem Sources 208 Acid Etching . 208 Fluting . 210 Inadequate Lubrication . 214 Looseness . 216 Bearings That Have Excessive Internal Clearance . 216 Bearings That are Turning on the Shaft . 219 Bearings Loose in the Housing . 220 Testing for Bearing Frequencies 220 Conclusion 222 CHAPTER SIX: ACCURATE EVALUATION OF GEARS Introduction .225 Data Acquisition 225 How To Take Data 225 Transducer Selection . 226 Gear Vibration Theory . 227 Evaluation of Gear Ratios . 227 Factoring 227 Gearmesh Frequency . 228 Fractional Gearmesh Frequency 229 Hunting Tooth Frequency . 230 Planetary Gears .231 Digression .233 End Digression .236 Gear Life Expectancy 242 Amplitude Modulation .243 The Gears Program 244 The AGMA Quality Number System 245 Gear Problems and Causes 246 Eccentric Gears . 246 Meshing Gears That Have a Common Factor and One Gear Is Eccentric 246Gears That Do Not Have a Common Factor and One or Both Gears Are Eccentric . 257 Gears That Are OutofRound or Have Several High Places 262 Gears Installed on a Bent Shaft 265 Loose and Worn Gears 268 Misaligned Gears 269 Backlash Problems or Oscillating Gears . 270 Broken. Cracked. or Chipped Teeth 274 Conclusion . 285 CHAPTER SEVEN: ANALYZING AND SOLVING PRESS ROLL AND NIP PROBLEMS Introduction 287 Vibration Theory of Rolls In Nip 288 Hardware 288 Software . 289 Synchronous Time Averaging . 289 Hardware Setup . 292 Dynamic Measurement of Rolls .294 Problems Associated with Rolls In Nip 297 Eccentric Rolls 297 Improper Ratios of Roll Sizes . 297 Resonant Frequencies . 299 Installation of Improperly Ground Rolls .301 Diagnosing Problems . 302 Data Collection and Analysis of Overall Vibration Data . 302 Relative Motion between Rolls 306 Conclusions and Recommendations 328 References 329 AppendixA 331 AppendixB .341 Glossary .343 Index . Y AC (Alternating Current) An electric current that reverses direction in a circuit at regular intervals. Acceleration The rate of change of velocity with respect to time. Accelerometer Any of various devices used to measure acceleration. ACCoupling A type of input that blocks the DC portion of the signal. AC voltage measurements Peaktopeak is the value of the total swing of the wave. Peak is onehalf of peaktopeak. Average is 0.637 x peak. RMS is 0.707 x peak. These values hold true for a true sine wave only. The more the signal deviates from a true sine wave, the greater the error in these calculations. AGMA gear quality number An established gear quality rating system for specifying gear quality numbers for different pitch line velocities (in feet/minute). Amplitude The maximum value of a periodically varying quantity. Analyzer The hardware unit used to analyze data. Analytical technique Solution of shock and vibration problems using mathematical analysis. Angular Velocity A vector quantity describing rotational motion, the magnitude of which is the time rate of change of angle and the direction of which is along the axis of rotation. Auto Abbreviation used for automatic. Average The arithmetic mean, as determined by the summation of the x's over n. Balls The balls in a bearing made from hardened metal alloys, sometimes used interchangeably with rollers when calculating bearing frequencies. Ball Pass Frequency The frequency balls or rollers pass over a single point on the inner or outer raceway of the bearing.Ball Pass Frequency of the Inner Race (BPFI) The frequency the balls or rollers pass over a single point on the inner raceway of a bearing. Ball Pass Frequency of the Outer Race (BPFO) The frequency the balls or rollers pass over a single point on the outer raceway of a bearing. Ball Spin Frequency (BSF) The number of revolutions per second made by a ball or roller in an antifriction bearing. Bandwidth refers to the overall range of frequencies, also refers to the range of frequencies between the half power points. Bandpass filter An electronic device used to filter all signals in a predetermined frequency range. Baseline Data The first or initial vibration data taken from a machine system. Beat The process of two frequenciesadding and subtracting as the signals go in and out of phase. Bump Test Measures the response of a component, machine, or structure when enough energy is introduced to excite the natural frequencies. Calibration The process of measuring the accuracy of an instrument. Cavitation When a pump is not operating at the correct point on the pump curve resulting in restricted suction intake, and the liquid tends to vaporize while coming off the impeller. Circumferential Crack A crack around the circumference of a roll. Clipping The truncation or flattening of the positive and/or negative portions of the signal, normally caused by overloading electronic circuits and machinery problems. Coastdown Data Starts the process of measuring the amplitude of vibration at all speeds from zero to operating speed. Contacting Displacement Transducer Also referred to as a LVDT (Linear Variable Differential Transformer). A transducer that is used to measure relative motion or displacement in the frequency range of 0 to 200 Hz. Crest factor One parameter used to describe the dynamic range of a voltmeter's amplifiers. Refers to a wave form and is the ratio of the peak to the RMS voltage with the dc component removed. The crest factor of a square wave is I, while that for a sine wave is 1.414. A pulse can have a crest factor of more than 9. Critical Damping The minimum viscous damping that allows a displaced system to return to its initial position.CF  P  DC RMS Critical speed Rotor speed at which local maximum amplitude occurs. A critical speed occurs whenever the rotor speed coincides with a system's natural frequency. Cycle A time interval in which a characteristic, especially a regularly repeated, event or sequence of events occurs. Damping A factor that causes a resonance or oscillation to decay over time. Data Acquisition The collection and processing of data. DC (direct current) A unidirectional current in which the changes in value are either zero or are so small that they may be ignored. Decibel (dB) Unit for measuring relative loudness of sound and electronic signals. The logarithmic expression of ratios, equal to onetenth of a Bell. The voltage ratio is: voltage output voltage input The power ratio is: p e r output power input where zero dB is always equal to one millivolt or one milliwatt. DC Coupling Uses a choke input that blocks the ac component and passes the dc component. Degrees of freedom The minimum number of independent coordinates required to define completely the positions of all parts of a system at any instant of time. Diameter The width of a circular object. Disk A wheel, usually solid and axially slim, on which mechanical work is performed, or from which work is extracted. Examples: Turbine disk, compressor wheel. Displacement Refers to the measurement of the distance an object moves. Duty cycle The pulse width divided by the pulse recurrence frequency or repetition rate, used in calculating the crest factor.Dynamic A state in which one or more quantities exhibits appreciable change within an arbitrarily short time interval. Dynamic Measurement An accurate measurement of a component while all the operational forces are applied. i.e. measuring the roundness of an operating roll or shaft. Dynamic Shape The resulting shape with all or some of the operational forces applied. Eccentric Gear A gear that does not conform to AGMA Quality Gear Standards. Eccentric Roll A roll that is not round. Empirical technique The measured response of a known defect. Engineering Units (EU) General term for the type of units used: GIs, mils, IPS, etc. Used when the type of units does not matter; for explanation or description. Excited Frequencies Natural or resonant frequencies excited by some source. Expanded Mode When only a portion of a signal is displayed on the grid, it is said to be expanded. Factor An integer that can be divided evenly into the number of interest and the quotient is an integer. Fast Fourier Transform A numerical calculation performed on a digitized time signal that creates a limited Fourier series of cosines and phase angles of each cosine. Fatigue Failure Failure of a mechanical component or system as a result of repeated stress cycles. Felt A fabric that supports the paper in a paper machine to assist the paper making process. Fiber Optic Sensor A device that uses a fiber optic light emitter and a fiber optic light sensor that can detect a difference between light and dark surfaces. Fluting Arcing from the inner race to the outer race through the rolling elements in a bearing which creates defects on the bearing raceways. Fractional Gearmesh Frequency A fraction of gearmesh frequency caused by eccentric gears and gears with improper ratios.Frequency The number of cycles present in a specific time period, normally one second. Measured in Hertz, which stands for cycles per second. Frequency is usually represented by the letter "F." The time period is represented by the Greek letter "tau" (T). The formulas are: Frequency Domain A term used to describe the magnitudes and frequencies of sinusoidal functions that once summed together make a time domain signal. Frequency Modulation Periodic changing of the frequency of a sinusoidal function over time. Frequency Range A specifically designated part of the frequency spectrum. Frequency Response The response (i.e., displacement, velocity, or acceleration) of a system described in terms of frequency. Forcing function The excitation of the vibration; the problem that is causing the vibration. Foundation Machine support. May be rigid or possess masselastic properties. Fourier series A mathematical description of a nonharmonic periodic function using a linear combination of sine and cosine functions. Full Scale The largest value indicated on the scale or in the case of instruments having their zero between the ends of the scale, the fullscale value. Fundamental Frequency The first harmonics or base frequency, such as gearmesh frequency, ball pass frequency, etc. Fundamental Train Frequency The angular velocity of the individual ball centers. Cage frequency. G Unit of measure used for acceleration measurements. Gear Life Expectancy The gear's life expectancy is reduced by the inverse of the common factor of the gears in mesh. Gearmesh frequency The angular speed of the rotating gear times the number of teeth on the gear. Generated Frequencies All frequencies that can be calculated and vary as a fuction of machine speed.Harmonic Exact multiples of a fundamental frequency. Harmonic analysis Anaiysis of a periodic complex wave form using sine and cosine functions. Harmonic Marker Lines displayed on the data used to identify the harmonic multiples (harmonics). Harmonic Motion The vibration motion of the projection upon a straight line of a point moving uniformly along a circumference in the same plane. He& The unit of frequency, one cycle per second. Housing A casing used to enclose a piece of machinery such as a motor or bearing. Hunting Tooth Frequency (HTF) The reciprocal of the time period one gear makes with a tooth on the other gear a second time. Imbalance A condition where there is more mass on one side of a rotating device than the other causing an outward radial force in the direction of the additional mass when the object is rotated. IPS (inches per second) Units used when measuring vibration in velocity. Journal Specific portions of a shaft surface from which rotor applied loads are transmitted to bearing support. L Lambda the greek letter I symbol for wavelength. Mesh The fitting of gears together, similar to fitting the fingers of two hands together. Mil Unit of measure, equal to a one thousandth of a second. Misalignment When two machines are coupled together and their axes of rotation are not aligned.Misaligned Gears Gears that are not meshing evenly across the pitch line. Msec An abbreviation for milliseconds or thousandths of a second. Modal Analysis A vibration response analysis that uses a unique combination of previously determined mode shapes for its mathematical description. Model A mathematical or experimental simulation of a component system. Modulation The act of mixing two or more frequencies. Amplitude modulation is a time varying amplitude. Frequency modulation is a time varying frequency. Motion Description of the displacement, velocity, or acceleration of a system as a function of time. Mv Abbreviation for millivolts, thousandths of a Volt. Natural Frequency The reciprocal of the natural period of a system. Nip The point of contact when two rolls are rotating in contact with each other. Noise Any disturbance, especially a random and persistent disturbance, that reduces the clarity or quality of a signal. Noncontacting Displacement Transducer A transducer that measures motions without contacting the target, the common name is proximity probe. Oil Whirl The shaft ridge on an oil wedge that whirls while it rotates; occurs in some lightly loaded, plain journal bearings. Oscillating Gears A condition where gears move from a point of contact between teeth in a direction of advance then bounce back in the opposite direction. OutofRound Rolls A roll whose center of rotation is not the geometric center of the roll. pp (peak to peak) Signal amplitude measurement, the maximum value of one cycle. Periodic Motion Oscillatory, periodic or repeating motion. Pitchline Velocity The tangential velocity of a rotating gear or bearing at the pitchline.Planetary Gears A system of gears where a central, sun gear rotates meshing with and turning a planetary gear whose axis of rotation moves around the sun gear. The planetary gear meshes with a ring gear which surrounds the planetary gears and the sun gear. Polar Plotting format which is circular. Measurements are in amplitude and degrees. Proximity Probe Ferromagnetic dynamic displacement transducer. Nonconducting displacement transducer used for measuring relative motion. Pseudo RMS Technique used by most analog meters to measure RMS. These meters multiply average by 1.11to present RMS measurements. This works for pure sine waves only. Pulse A transient amplification or intensificationof a characteristicof a system,especially of a wave characteristic, followed by return to equilibrium or steady state. Radial Load A load that is directed toward the center of the axis of rotation. Random Motion Motion that is not repetitive in magnitude or frequency of occurrence. Range The set of values lying between the upper and lower limits. Realtime Pertaining to the actual time during which a physical process transpires. Relative Motion The motion of one body with respect to another disregarding any motion relative to a third point or reference. Relative Motion Measurement The measurement of the motion of one body with respect to another usually performed with a contacting or noncontacting displacement transducer. Resonance The enhancement of the response of an electric or mechanical system to a periodic driving force when the driving frequency is equal to the natural undamped frequency of the system. Resonant Frequency The frequency of the resonance. Root Mean Square (RMS) A method of measuring the true energy under the curve. The half power point of a sinusoid or .707times the peak value of a pure sinusoid.Rotor Bars The ferromagnetic bars in the rotor of an electric motor. RPM An abbreviation used for Revolutions Per Minute. Shallow Flaking A defect in a bearing raceway where the bearing raceway is missing shallow flakes of metal. Shock A nonperiodic excitationof a mechanical system characterizedby sudden loading. Shock absorber A device that dissipates energy in order to modify the response of a mechanical system to applied shock. Shock isolater A resilient support that isolates a system from a shock loading. Shock pulse A substantial disturbance characterized by rise and decay of acceleration in a short period. Shock spectrum The maximum response (acceleration, velocity, or displacement) of a seriesof damped or undamped singledegreeoffreedom systems resulting from a specific shock excitation. An independent massspringdamper system is associated with each frequency. Signaltonoise Ratio The ratio of signal levels to noise level. Sinusoidal A description for a phenomenon that follows a sine function or a cosine function. Siren Effect A generated frequency equal to the number of bars/slots in a rotor times the rotating speed. +slope Refers to the portion above zero in the yaxis direction. slope Refers to the portion below zero in the yaxis direction. Spectra Plural of spectrum. Spectral lines An isolated peak of intensity in a spectrum. Spectrum The distribution of amplitude as a function of frequency. Speed The distance covered by a point divided by the time required to cover that distance defined for an instant in time. Square Wave A rectangular wave or near rectangular wave that rises to a positive level flat peak for a period of time then falls to a negative level flat peak for a period of time and repeats itself. Contains odd harmonics sometimes called odd fractions.StartupData Vibration data taken on a machine as the machine goes from zero rotational velocity up to operating speed. Starvation This occurs in pumps when there is not enough liquid present to fill each vane on the impeller every revolution. Stiffness The description of the elastic properties of a system given in terms of pounds force per inch of deflection. Synchronous Time Averaging Method of time averaging to average out nonsynchronous vibration. Thrust Load A load on a machine that is in the axial direction. Time Delay The time interval between the starting point of a signal and the detection of the trigger. Time Domain The signal level with respect to time. Transducer An electronic device that converts a mechanical vibration or motion into an electronic signal. Transducer Sensitivity Used to transform the voltage output of a transducer to the appropriate engineering units (V/E). Trigger A pulse or signal used to initiate data collection. A triggered sweep or delay ramp. Truncation Signals that have the peaks cut off at some level. Time The inverse of frequency. The continuous passage measured in seconds, minutes, hours. Vane pass frequency The frequency at which the blades of a pump pass a particular point. Velocity The speed or how fast an object is moving. Velocity Transducer Unit used to measure the vibration velocity of an object. Vibration The physical motion of a rotating machine. Volt The difference of electric potential between two points of a conductor carrying a constant current of one ampere, when the power dissipated between these points is equal to one watt.Voltage The dot product line integral of the electric field strength along its path. Measured in volts. Wavelength In a periodic wave, the distance between two points of corresponding phase in consecutive cycles. Xaxis The horizontal direction on the grid. Xscale The minimum and maximum scaled values used on the xaxis of the grid. Yaxis The vertical direction on the grid. Yscale The minimum and maximum scale values used on the yaxis of the grid. Zp (zero to peak) Signal amplitude measurement from the zero reference to the maximum or minimum value of the signal. Zoom Also called frequency translation. When data is collected on a range other than between zero and the bandwidth, it is called a zoom. A zoom is different from an expand. The zoom mode increases the resolution, where the expanded mode does not.
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كاتب الموضوع  رسالة 

Admin مدير المنتدى
عدد المساهمات : 18805 تاريخ التسجيل : 01/07/2009
 موضوع: كتاب The Vibration Analysis Handbook الثلاثاء 31 يناير 2012, 1:45 am  

أخواني في الله أحضرت لكم كتاب The Vibration Analysis Handbook First Edition Second Printing
و المحتوى كما يلي :
TABLE OF CONTENTS CHAPTER ONE: INTRODUCTION TO MACHINERY VIBRATION TheoryofVibration . 1 HarmonicMotion . 1 Periodic Motion 1 RandomMotion 3 The Relationship between Time and Frequency 3 Time . 3 Frequency . 4 Amplitude Measurement . 6 Sources of Frequencies . 8 Generated Frequencies . 8 Excited Frequencies . 9 Frequencies Caused by Electronic Phenomena 17 ForcingFunction . 20 Combinations of Machine Problems 21 Mixing Frequencies . 22 Electrical and Mechanical Relationship 23 Time and Frequency Domain . 24 Relationship between Velocity. Displacement. and Acceleration . 25 Units of Measurement . 27 Relationships . 27 Ways of Measuring Vibration . 32 Relation between Diameter. Speed. and RPM . 32 How To Determine Machine Speed in FPM from the Vibration Data . 33 Conclusion and Efficiencies . 34 CHAPTER TWO: TIME AND FREQUENCY ANALYSIS TECHNIQUES Introduction 35 Basicphysics 35 Single Frequency . 36 Single Frequency with Harmonics 41 Clipping .52 SquareWave 52 Natural Frequencies 55 Multiple Frequencies.Linear Systems 55 High Frequency Riding a Low Frequency 55 Multiple Frequencies.Nonlinear Systems . 56 AmplitudeModulation 57 Sum and Difference Frequencies .61 Pulses .65 FrequencyModulation 67 Conclusion .68CHAPTER THREE: HARDWARE AND SOFTWARE REQUIRED FOR ACCURATE DIAGNOSTICS Hardware 71 Introduction 71 Personal Computer . 72 Realtime Analyzer . 73 Datacollection 76 Printers 78 Transducers 78 Displacement Transducers . 79 Velocity Transducers 81 Accelerometers 82 Pressure Transducers . 83 Microphones 83 OncePerRevolution Markers . 84 Multiplexer . 85 Gauss Meter 87 Software . 87 Introduction 87 Group 1. Toolbox Software . 90 Signal Analysis Program . 90 Vibration Calculation Program 90 Resonance and Deflection Calculator (RADC) . 92 Bearing Calculation Program . 92 Gears Program 95 Roll Ratio Program and Rusch Chart . 97 Group 2. Machine Doctor (MACHDOC) . 98 MACHDOC 98 Polar Plot . 100 Time Plot . 102 Balancing . 102 Diagnostic Database . 103 Diagnostic Modules . 108 Roll Quality Assurance Program . 109 Group3 110 Group4 110 CHAPTER FOUR: ACCURATE EVALUATION OF MACHINERY CONDITION Introduction .111 Theory .111 Calibration 115 Frequencies Generated . 116 Datacollection .117 Transducer Selection .118 Continuous Monitoring . 118 CommonProblems 119Imbalance 119 Bentshaft 119 SoftFoot . 122 Misalignment . 122 Looseness 125 Bearings Loose on the Shaft 125 Bearings Loose in the Housing 126 Common Forms of Looseness . 128 Noise . 128 Diagnosis of Looseness 129 Resonance 129 Rubs 130 Problems That Cause Pulses 130 OilWhirl 134 Analysis of Electric Motors . 135 Motors OutofMagnetic Center . 136 Broken Rotor Bars . 139 TurnToTurn Shorts in Windings 143 Vibration Problems in Synchronous Motors 144 SirenEffect . 146 Solo Data on Motors 146 Steam Turbines 148 Pumps 150 Impeller Contact .150 Starvation 151 Cavitation 152 Compressors 152 Fans 154 Special Tests 155 Startup/Coast Down Data . 155 Bump Tests .158 Noise Recording .160 Synchronous Time Averaging (STA) 161 Relative Motion Measurements (RMM) 164 CHAPTER FIVE: ACCURATE DIAGNOSIS OF ANTIFRICTION BEARINGS Introduction 167 Datacollection 167 Transducer Selection 167 Generated Frequencies 167 Fundamental Train Frequency 168 Ball Pass Frequency of Outer Race .169 Ball Pass Frequency of Inner Race .170 Ball Spin Frequency 170 Application of the Bearing Formulas .172 Outer Race Analysis 175 Inner Race Analysis 176 Ball Spin Frequency Analysis .176 Fundamental Train Frequency Analysis . 177VCI Bearing Calculation Program 177 Bearing Defects . 178 Raceways . 178 Outer Race 178 InnerRace . 181 Outer and Inner Race Amplitude . 185 Modulation of Ball Pass Frequency 185 Rolling Elements. Balls. and Rollers . 186 Cage . 189 Multiple Defects 189 Progressive Bearing Failure 193 Defectseverity . 196 Bearing Behavior 196 Inner Race Defect Length . 197 Defect Length Calculation . 201 Deep Fatigue Spalls vs.Shallow Flaking 203 Problem Sources 208 Acid Etching . 208 Fluting . 210 Inadequate Lubrication . 214 Looseness . 216 Bearings That Have Excessive Internal Clearance . 216 Bearings That are Turning on the Shaft . 219 Bearings Loose in the Housing . 220 Testing for Bearing Frequencies 220 Conclusion 222 CHAPTER SIX: ACCURATE EVALUATION OF GEARS Introduction .225 Data Acquisition 225 How To Take Data 225 Transducer Selection . 226 Gear Vibration Theory . 227 Evaluation of Gear Ratios . 227 Factoring 227 Gearmesh Frequency . 228 Fractional Gearmesh Frequency 229 Hunting Tooth Frequency . 230 Planetary Gears .231 Digression .233 End Digression .236 Gear Life Expectancy 242 Amplitude Modulation .243 The Gears Program 244 The AGMA Quality Number System 245 Gear Problems and Causes 246 Eccentric Gears . 246 Meshing Gears That Have a Common Factor and One Gear Is Eccentric 246Gears That Do Not Have a Common Factor and One or Both Gears Are Eccentric . 257 Gears That Are OutofRound or Have Several High Places 262 Gears Installed on a Bent Shaft 265 Loose and Worn Gears 268 Misaligned Gears 269 Backlash Problems or Oscillating Gears . 270 Broken. Cracked. or Chipped Teeth 274 Conclusion . 285 CHAPTER SEVEN: ANALYZING AND SOLVING PRESS ROLL AND NIP PROBLEMS Introduction 287 Vibration Theory of Rolls In Nip 288 Hardware 288 Software . 289 Synchronous Time Averaging . 289 Hardware Setup . 292 Dynamic Measurement of Rolls .294 Problems Associated with Rolls In Nip 297 Eccentric Rolls 297 Improper Ratios of Roll Sizes . 297 Resonant Frequencies . 299 Installation of Improperly Ground Rolls .301 Diagnosing Problems . 302 Data Collection and Analysis of Overall Vibration Data . 302 Relative Motion between Rolls 306 Conclusions and Recommendations 328 References 329 AppendixA 331 AppendixB .341 Glossary .343 Index . Y AC (Alternating Current) An electric current that reverses direction in a circuit at regular intervals. Acceleration The rate of change of velocity with respect to time. Accelerometer Any of various devices used to measure acceleration. ACCoupling A type of input that blocks the DC portion of the signal. AC voltage measurements Peaktopeak is the value of the total swing of the wave. Peak is onehalf of peaktopeak. Average is 0.637 x peak. RMS is 0.707 x peak. These values hold true for a true sine wave only. The more the signal deviates from a true sine wave, the greater the error in these calculations. AGMA gear quality number An established gear quality rating system for specifying gear quality numbers for different pitch line velocities (in feet/minute). Amplitude The maximum value of a periodically varying quantity. Analyzer The hardware unit used to analyze data. Analytical technique Solution of shock and vibration problems using mathematical analysis. Angular Velocity A vector quantity describing rotational motion, the magnitude of which is the time rate of change of angle and the direction of which is along the axis of rotation. Auto Abbreviation used for automatic. Average The arithmetic mean, as determined by the summation of the x's over n. Balls The balls in a bearing made from hardened metal alloys, sometimes used interchangeably with rollers when calculating bearing frequencies. Ball Pass Frequency The frequency balls or rollers pass over a single point on the inner or outer raceway of the bearing.Ball Pass Frequency of the Inner Race (BPFI) The frequency the balls or rollers pass over a single point on the inner raceway of a bearing. Ball Pass Frequency of the Outer Race (BPFO) The frequency the balls or rollers pass over a single point on the outer raceway of a bearing. Ball Spin Frequency (BSF) The number of revolutions per second made by a ball or roller in an antifriction bearing. Bandwidth refers to the overall range of frequencies, also refers to the range of frequencies between the half power points. Bandpass filter An electronic device used to filter all signals in a predetermined frequency range. Baseline Data The first or initial vibration data taken from a machine system. Beat The process of two frequenciesadding and subtracting as the signals go in and out of phase. Bump Test Measures the response of a component, machine, or structure when enough energy is introduced to excite the natural frequencies. Calibration The process of measuring the accuracy of an instrument. Cavitation When a pump is not operating at the correct point on the pump curve resulting in restricted suction intake, and the liquid tends to vaporize while coming off the impeller. Circumferential Crack A crack around the circumference of a roll. Clipping The truncation or flattening of the positive and/or negative portions of the signal, normally caused by overloading electronic circuits and machinery problems. Coastdown Data Starts the process of measuring the amplitude of vibration at all speeds from zero to operating speed. Contacting Displacement Transducer Also referred to as a LVDT (Linear Variable Differential Transformer). A transducer that is used to measure relative motion or displacement in the frequency range of 0 to 200 Hz. Crest factor One parameter used to describe the dynamic range of a voltmeter's amplifiers. Refers to a wave form and is the ratio of the peak to the RMS voltage with the dc component removed. The crest factor of a square wave is I, while that for a sine wave is 1.414. A pulse can have a crest factor of more than 9. Critical Damping The minimum viscous damping that allows a displaced system to return to its initial position.CF  P  DC RMS Critical speed Rotor speed at which local maximum amplitude occurs. A critical speed occurs whenever the rotor speed coincides with a system's natural frequency. Cycle A time interval in which a characteristic, especially a regularly repeated, event or sequence of events occurs. Damping A factor that causes a resonance or oscillation to decay over time. Data Acquisition The collection and processing of data. DC (direct current) A unidirectional current in which the changes in value are either zero or are so small that they may be ignored. Decibel (dB) Unit for measuring relative loudness of sound and electronic signals. The logarithmic expression of ratios, equal to onetenth of a Bell. The voltage ratio is: voltage output voltage input The power ratio is: p e r output power input where zero dB is always equal to one millivolt or one milliwatt. DC Coupling Uses a choke input that blocks the ac component and passes the dc component. Degrees of freedom The minimum number of independent coordinates required to define completely the positions of all parts of a system at any instant of time. Diameter The width of a circular object. Disk A wheel, usually solid and axially slim, on which mechanical work is performed, or from which work is extracted. Examples: Turbine disk, compressor wheel. Displacement Refers to the measurement of the distance an object moves. Duty cycle The pulse width divided by the pulse recurrence frequency or repetition rate, used in calculating the crest factor.Dynamic A state in which one or more quantities exhibits appreciable change within an arbitrarily short time interval. Dynamic Measurement An accurate measurement of a component while all the operational forces are applied. i.e. measuring the roundness of an operating roll or shaft. Dynamic Shape The resulting shape with all or some of the operational forces applied. Eccentric Gear A gear that does not conform to AGMA Quality Gear Standards. Eccentric Roll A roll that is not round. Empirical technique The measured response of a known defect. Engineering Units (EU) General term for the type of units used: GIs, mils, IPS, etc. Used when the type of units does not matter; for explanation or description. Excited Frequencies Natural or resonant frequencies excited by some source. Expanded Mode When only a portion of a signal is displayed on the grid, it is said to be expanded. Factor An integer that can be divided evenly into the number of interest and the quotient is an integer. Fast Fourier Transform A numerical calculation performed on a digitized time signal that creates a limited Fourier series of cosines and phase angles of each cosine. Fatigue Failure Failure of a mechanical component or system as a result of repeated stress cycles. Felt A fabric that supports the paper in a paper machine to assist the paper making process. Fiber Optic Sensor A device that uses a fiber optic light emitter and a fiber optic light sensor that can detect a difference between light and dark surfaces. Fluting Arcing from the inner race to the outer race through the rolling elements in a bearing which creates defects on the bearing raceways. Fractional Gearmesh Frequency A fraction of gearmesh frequency caused by eccentric gears and gears with improper ratios.Frequency The number of cycles present in a specific time period, normally one second. Measured in Hertz, which stands for cycles per second. Frequency is usually represented by the letter "F." The time period is represented by the Greek letter "tau" (T). The formulas are: Frequency Domain A term used to describe the magnitudes and frequencies of sinusoidal functions that once summed together make a time domain signal. Frequency Modulation Periodic changing of the frequency of a sinusoidal function over time. Frequency Range A specifically designated part of the frequency spectrum. Frequency Response The response (i.e., displacement, velocity, or acceleration) of a system described in terms of frequency. Forcing function The excitation of the vibration; the problem that is causing the vibration. Foundation Machine support. May be rigid or possess masselastic properties. Fourier series A mathematical description of a nonharmonic periodic function using a linear combination of sine and cosine functions. Full Scale The largest value indicated on the scale or in the case of instruments having their zero between the ends of the scale, the fullscale value. Fundamental Frequency The first harmonics or base frequency, such as gearmesh frequency, ball pass frequency, etc. Fundamental Train Frequency The angular velocity of the individual ball centers. Cage frequency. G Unit of measure used for acceleration measurements. Gear Life Expectancy The gear's life expectancy is reduced by the inverse of the common factor of the gears in mesh. Gearmesh frequency The angular speed of the rotating gear times the number of teeth on the gear. Generated Frequencies All frequencies that can be calculated and vary as a fuction of machine speed.Harmonic Exact multiples of a fundamental frequency. Harmonic analysis Anaiysis of a periodic complex wave form using sine and cosine functions. Harmonic Marker Lines displayed on the data used to identify the harmonic multiples (harmonics). Harmonic Motion The vibration motion of the projection upon a straight line of a point moving uniformly along a circumference in the same plane. He& The unit of frequency, one cycle per second. Housing A casing used to enclose a piece of machinery such as a motor or bearing. Hunting Tooth Frequency (HTF) The reciprocal of the time period one gear makes with a tooth on the other gear a second time. Imbalance A condition where there is more mass on one side of a rotating device than the other causing an outward radial force in the direction of the additional mass when the object is rotated. IPS (inches per second) Units used when measuring vibration in velocity. Journal Specific portions of a shaft surface from which rotor applied loads are transmitted to bearing support. L Lambda the greek letter I symbol for wavelength. Mesh The fitting of gears together, similar to fitting the fingers of two hands together. Mil Unit of measure, equal to a one thousandth of a second. Misalignment When two machines are coupled together and their axes of rotation are not aligned.Misaligned Gears Gears that are not meshing evenly across the pitch line. Msec An abbreviation for milliseconds or thousandths of a second. Modal Analysis A vibration response analysis that uses a unique combination of previously determined mode shapes for its mathematical description. Model A mathematical or experimental simulation of a component system. Modulation The act of mixing two or more frequencies. Amplitude modulation is a time varying amplitude. Frequency modulation is a time varying frequency. Motion Description of the displacement, velocity, or acceleration of a system as a function of time. Mv Abbreviation for millivolts, thousandths of a Volt. Natural Frequency The reciprocal of the natural period of a system. Nip The point of contact when two rolls are rotating in contact with each other. Noise Any disturbance, especially a random and persistent disturbance, that reduces the clarity or quality of a signal. Noncontacting Displacement Transducer A transducer that measures motions without contacting the target, the common name is proximity probe. Oil Whirl The shaft ridge on an oil wedge that whirls while it rotates; occurs in some lightly loaded, plain journal bearings. Oscillating Gears A condition where gears move from a point of contact between teeth in a direction of advance then bounce back in the opposite direction. OutofRound Rolls A roll whose center of rotation is not the geometric center of the roll. pp (peak to peak) Signal amplitude measurement, the maximum value of one cycle. Periodic Motion Oscillatory, periodic or repeating motion. Pitchline Velocity The tangential velocity of a rotating gear or bearing at the pitchline.Planetary Gears A system of gears where a central, sun gear rotates meshing with and turning a planetary gear whose axis of rotation moves around the sun gear. The planetary gear meshes with a ring gear which surrounds the planetary gears and the sun gear. Polar Plotting format which is circular. Measurements are in amplitude and degrees. Proximity Probe Ferromagnetic dynamic displacement transducer. Nonconducting displacement transducer used for measuring relative motion. Pseudo RMS Technique used by most analog meters to measure RMS. These meters multiply average by 1.11to present RMS measurements. This works for pure sine waves only. Pulse A transient amplification or intensificationof a characteristicof a system,especially of a wave characteristic, followed by return to equilibrium or steady state. Radial Load A load that is directed toward the center of the axis of rotation. Random Motion Motion that is not repetitive in magnitude or frequency of occurrence. Range The set of values lying between the upper and lower limits. Realtime Pertaining to the actual time during which a physical process transpires. Relative Motion The motion of one body with respect to another disregarding any motion relative to a third point or reference. Relative Motion Measurement The measurement of the motion of one body with respect to another usually performed with a contacting or noncontacting displacement transducer. Resonance The enhancement of the response of an electric or mechanical system to a periodic driving force when the driving frequency is equal to the natural undamped frequency of the system. Resonant Frequency The frequency of the resonance. Root Mean Square (RMS) A method of measuring the true energy under the curve. The half power point of a sinusoid or .707times the peak value of a pure sinusoid.Rotor Bars The ferromagnetic bars in the rotor of an electric motor. RPM An abbreviation used for Revolutions Per Minute. Shallow Flaking A defect in a bearing raceway where the bearing raceway is missing shallow flakes of metal. Shock A nonperiodic excitationof a mechanical system characterizedby sudden loading. Shock absorber A device that dissipates energy in order to modify the response of a mechanical system to applied shock. Shock isolater A resilient support that isolates a system from a shock loading. Shock pulse A substantial disturbance characterized by rise and decay of acceleration in a short period. Shock spectrum The maximum response (acceleration, velocity, or displacement) of a seriesof damped or undamped singledegreeoffreedom systems resulting from a specific shock excitation. An independent massspringdamper system is associated with each frequency. Signaltonoise Ratio The ratio of signal levels to noise level. Sinusoidal A description for a phenomenon that follows a sine function or a cosine function. Siren Effect A generated frequency equal to the number of bars/slots in a rotor times the rotating speed. +slope Refers to the portion above zero in the yaxis direction. slope Refers to the portion below zero in the yaxis direction. Spectra Plural of spectrum. Spectral lines An isolated peak of intensity in a spectrum. Spectrum The distribution of amplitude as a function of frequency. Speed The distance covered by a point divided by the time required to cover that distance defined for an instant in time. Square Wave A rectangular wave or near rectangular wave that rises to a positive level flat peak for a period of time then falls to a negative level flat peak for a period of time and repeats itself. Contains odd harmonics sometimes called odd fractions.StartupData Vibration data taken on a machine as the machine goes from zero rotational velocity up to operating speed. Starvation This occurs in pumps when there is not enough liquid present to fill each vane on the impeller every revolution. Stiffness The description of the elastic properties of a system given in terms of pounds force per inch of deflection. Synchronous Time Averaging Method of time averaging to average out nonsynchronous vibration. Thrust Load A load on a machine that is in the axial direction. Time Delay The time interval between the starting point of a signal and the detection of the trigger. Time Domain The signal level with respect to time. Transducer An electronic device that converts a mechanical vibration or motion into an electronic signal. Transducer Sensitivity Used to transform the voltage output of a transducer to the appropriate engineering units (V/E). Trigger A pulse or signal used to initiate data collection. A triggered sweep or delay ramp. Truncation Signals that have the peaks cut off at some level. Time The inverse of frequency. The continuous passage measured in seconds, minutes, hours. Vane pass frequency The frequency at which the blades of a pump pass a particular point. Velocity The speed or how fast an object is moving. Velocity Transducer Unit used to measure the vibration velocity of an object. Vibration The physical motion of a rotating machine. Volt The difference of electric potential between two points of a conductor carrying a constant current of one ampere, when the power dissipated between these points is equal to one watt.Voltage The dot product line integral of the electric field strength along its path. Measured in volts. Wavelength In a periodic wave, the distance between two points of corresponding phase in consecutive cycles. Xaxis The horizontal direction on the grid. Xscale The minimum and maximum scaled values used on the xaxis of the grid. Yaxis The vertical direction on the grid. Yscale The minimum and maximum scale values used on the yaxis of the grid. Zp (zero to peak) Signal amplitude measurement from the zero reference to the maximum or minimum value of the signal. Zoom Also called frequency translation. When data is collected on a range other than between zero and the bandwidth, it is called a zoom. A zoom is different from an expand. The zoom mode increases the resolution, where the expanded mode does not.
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