CAT III Key Points PDF

Key points Key points CAT III key points Page 3 The ‘key points’ are provided throughout the Category III course and give students a guide to what topics are required to be known as per ISO 18436-2. They are an excelle...

Key points Key points CAT III key points Page 3 The ‘key points’ are provided throughout the Category III course and give students a guide to what topics are required to be known as per ISO 18436-2. They are an excellent resource for checking your understanding as the course progresses and as a study guide for those taking the exam. This document summarises the key points slides from all of the Category III lessons. Condition monitoring program  The Category III analyst is responsible for setting up and managing CM programs  ISO and other standards are available to guide you  You must choose the correct maintenance strategies based on  Criticality  P-F Interval  Failure modes  The maintenance strategies are  Run to failure (very low criticality)  Preventive (age-related failure modes)  Condition based  Performing proactive tasks and performing maintenance with precision are key to reliability  You must choose the correct monitoring technologies and know where and when to apply them  Managing a CM program involves such things as  Defining standard tests  Defining test frequency  Setting up and managing the database  Setting and refining alarms  Writing reports  Follow up and review  Promoting the program  Educating others Ultrasound  Instrument converts very high frequencies to sounds you can hear  Primary use is for listening for signs of faults, but amplitude readings and waveforms can be captured  Can be used in contact and airborne applications  Key features include:  Directional  Sounds travels through physical objects (unlike infrared)  Useful in high noise environments  Applications include:  Detecting bearing and lubrication problems  Detecting steam, air and gas leaks  Detecting faulty steam traps  Detecting corona, tracking and arcing electrical faults  Can be used while greasing bearings [email protected] Copyright ©2020 Mobius Institute www.mobiusinstitute.com Page 4 CAT III key points Condition monitoring technologies Thermography  Thermography (infrared imaging) provides a relatively inexpensive way to detect changes in temperature  Cameras range greatly in capability - it is important to match the right camera with the application  Certain principles should be understood to avoid costly errors  Transmission, absorption, reflection, emission  Emissivity, resolution, zoom  Test conditions can significantly affect the readings obtained  Wind, sunlight, ambient temperature, angle to target  Applications include detection of:  Mechanical wear  Steam trap malfunction and other process applications  A range of electrical faults Electric motors  Special tests can be performed to detect electro-mechanical faults  Broken rotor-bars and end-rings  Rotor, stator, winding, lamination and connection issues  Power supply issues  Motor Current Analysis [MCA]  Analyze one phase typically with a CT + vibration analyzer  Electrical Signature Analysis [ESA]  Three phases of voltage and current for motor and supply issues  Motor Circuit Analysis [MCA]  Test performed off-line Oil analysis  Oil analysis has three benefits:  Check the chemistry/condition of the oil  Check for contamination  Check for wear  Oil analysis is not the best check of wear  It can only detect particles up to 8-10 microns in size  Test must be performed correctly  Analysis can be performed by an oil lab or using on-site instruments Wear particle analysis  Wear particle analysis utilizes a microscope to view microscopic particles on a specially prepared slide  Wear particle analysis can be performed by an outside laboratory or by using a patch/filter kit and an affordable microscope  Wear particle analysis can be used to determine:  Nature and severity of wear  Components that are undergoing wear  Can be performed on lubricating oil and hydraulic fluid  Wear particle analysis is essential for critical gearboxes  Standard oil analysis is not the best check of wear  It can only detect particles up to 8-10 microns in size [email protected] Copyright ©2020 Mobius Institute www.mobiusinstitute.com CAT III key points Page 5 Signal processing Introduction  Students should understand the basic order of steps involved in signal processing  Students should be able to recognize the high pass, low pass and band pass filters  Students should be aware of filter characteristics and design issues including transition band, stop band, phase accuracy etc.  Be aware of digital and analog filters  Students should understand the difference between digital and analog integration  What happens at very low frequencies and at high frequencies when data is integrated?  Why is a (10 Hz) high pass filter often used when integrating data?  What happens if you want to measure low frequencies? Dynamic range  The dynamic range is the ratio of the largest to the smallest signal that can be measured  It is given in dB  It is related to the number of bits in the A/D converter  Signal to noise (S/N) ratio is the ratio of the largest to the smallest amplitude in a particular measurement  Signal conditioning is used to improve the S/N ratio. It includes:  Analog integration  Filtering  Auto ranging  Using the correct sensor etc.  Some signal conditioning strategies become less important if you have a greater dynamic range Aliasing  Students will need to understand the formula below  It will be provided on the exam  Students should be familiar with the FFT  N values go in (e.g. the digitized time waveform)  N/2 amplitude and N/2 phase values are computed (the spectrum)  N/2.56 values are kept to avoid aliasing  Students must be familiar with the Nyquist criterion  Sampling rate and aliasing  Understand the Delta - Sigma method Sampling and resolution  Students will need to understand the relationship between sample time (T) and lines of resolution (LOR) and between LOR and N  Understand what is meant by resolution in the spectrum  R = Fmax / LOR  A smaller “R” is a “higher” resolution  Understand that more isn’t always better  1/R=T  This means a higher resolution spectrum takes more time to collect [email protected] Copyright ©2020 Mobius Institute www.mobiusinstitute.com Page 6 CAT III key points Signal processing… Windowing  Students should understand the purpose of using Windows  The Hanning window solves the leakage problem  Every window provides a trade off in frequency vs amplitude accuracy  The window factor (WF) must be accounted for when calculating graph resolution (R)  Bandwidth = R x WF  To separate two peaks in a spectrum  SF > 2 x Fmax / LOR x WF  Window summary  Flat top  Good amplitude but poor frequency  Used for calibrating sensors  Rectangular  Good frequency - used for bump tests and hammer tests  Exponential  Used for response channel in force response test  Damps vibration down before end of time block  Hanning/Hamming  Used for route testing rotating equipment  Good trade-off between frequency and amplitude accuracy  Reduces leakage Averaging  Students should understand the concept of averaging and understand why averaging is used  Averaging reduces but does not remove noise  Students should be familiar with the different averaging types and their applications  Students should understand the process involved in deciding how many averages to collect  Students should be comfortable with the concept of overlap averaging  Students should be able to calculate the total time to collect a reading with and without overlap averaging  Understand that overlap averaging uses the data thrown away by the Hanning window Triggering, TSA, autocorrelation, order tracking  Students should be aware of advanced signal processing techniques and their applications including:  Triggering  Time synchronous averaging (TSA)  Use of tracking ratio synthesizers  Autocorrelation  Order tracking  Students should not only understand when to use these techniques but they should know how they work and understand any issues associated with them [email protected] Copyright ©2020 Mobius Institute www.mobiusinstitute.com CAT III key points Page 7 Time waveform analysis Time waveform settings  In Category II you learned to configure the data collector settings to optimize the spectrum for analysis. In this course students should understand how to configure the settings to optimize the time waveform for analysis.  Students should understand the key attributes of the time waveform  Time record length (T)  Time between samples or sample period (Ts)  Students should be able to set up tests to capture gear mesh frequencies, a certain number of shaft revolutions or other key events  Students should understand the relationship between the time waveform and the spectrum and between the time waveform and analyzer settings as described by the formula below  The formula will be provided in the exam  Students should understand the importance of choosing the correct measurement units (A, V, D) Time waveform analysis  Students should understand the relationship between period and frequency (P seconds = 1 / F Hz)  Calculate frequencies from events in the waveform  Calculate period of shaft rate or gearmesh frequency etc.  Use this information to choose appropriate measurement settings  Students should be able to recognize important patterns in time waveforms such as:  Impacts, modulation, transients, beating, asymmetry etc.  Students should be aware of the relationship between the patterns listed above and common machine faults:  Gearboxes, bearings, looseness, misalignment, unbalance, cavitation, damaged belts etc.  Students should appreciate that some mechanical faults are more easily detected in the time waveform than the spectrum Circle plots  Students should be aware of the circular plot as an option for plotting time waveform data  The circular plot is especially useful in identifying synchronous events Phase analysis Introduction  Students should be aware of the various applications for phase readings  Students should understand the definition of phase  One cycle of vibration is 360 degrees  Phase is the relative timing between two signals  Students should understand how phase is measured using a tachometer or keyphasor  Students should understand the concept of leading and lagging phase  The more common convention is when the tachometer signal leads, the angle is positive [email protected] Copyright ©2020 Mobius Institute www.mobiusinstitute.com Page 8 CAT III key points Phase analysis… Representing phase  Students should understand that the measured phase angle will change if the position of the phase reference changes  Phase readings change depending on the units  Acceleration leads velocity by 90 degrees and velocity leads displacement by 90 degrees  In most cases the units don’t matter as long as we don’t change them because we are interested in relative phase  When balancing a rotor it is important to know where the “heavy spot” is in order to determine where to place a trial weight  In this case it is important to understand the relationship between phase and units  Students should understand how to represent phase data as vectors and in bubble diagrams Measuring phase  Students should understand the various ways to measure phase using a once per rev reference such as a tachometer, keyphasor or strobe light  Students should understand relative phase  Students should be aware of how sensor orientation effects phase  Students should understand when to use relative phase and when to use absolute phase measurements Fault diagnosis  Students should understand the common machine faults discussed in this section  Students should be able to diagnose these faults using bubble diagrams  Students should understand how phase relationships can be used to distinguish between common faults such as eccentricity, unbalance and misalignment  Students should be able to interpret bubble diagrams and understand how the structure or machine is moving based on the phase and amplitude reading System dynamics Undamped natural frequency  Students should be familiar with the concept of the un damped natural frequency  Students should be familiar with the formulas below and should understand the relationship between mass, stiffness and natural frequency Damping  Students should be familiar with the concept of damping  Damping is the conversion of mechanical energy into heat  Students should be familiar with the three kinds of damping:  Viscous  Frictional  Hysteresis  Students should be able to provide examples of these types of damping [email protected] Copyright ©2020 Mobius Institute www.mobiusinstitute.com CAT III key points Page 9 System dynamics… Single degree of freedom (SDOF)  Students should be familiar with the definition of a single degree of freedom system (SDOF)  Students should understand each term / variable in the formula below  Students should understand the meaning of each section of the formula and be able to relate it to a mass spring system  Students should be aware that the dot above the “x” in the formula refers to differentiation, or “rate of change of”, which is the opposite of integration Damping ratio  Students should know the difference between critically damped, over damped and under damped systems  Students should understand (the minimal) effect damping has on the natural frequency  Students should understand the relationship between damping and the time it takes for a signal to decay  Students should be familiar with the variables in the formulas below and should be able to interpret them Magnitude, phase and damping  Students should understand how the phase and amplitudes change as one passes through a natural frequency  Students should understand that amplitude and phase can be represented in a variety of ways including as a vector and as real and imaginary values  Amplitudes and Phase can be represented on a number of different plots including: Bodé plot and Nyquist/polar plot  Students should be familiar with and know how to interpret the Bodé plot and Nyquist/polar plot  Resonance occurs when a natural frequency is excited by a forcing frequency  Students should understand the effect of damping at a natural frequency Dynamics of the rotor  Students should know the definition of rigid and flexible rotors and how this relates to critical speeds  Students should understand the terms “high spot” and “heavy spot”  Students should understand the concept of leading and lagging phase  With reference to the high spot and heavy spot  With reference to a critical speed  With reference to the Bodé plot and Nyquist plot  Students should understand other sources of phase lag  Students should understand qualitatively how a rotor rotates above and below its first critical speed  Below it rotates around its center of geometry  Above it rotates round its center of mass [email protected] Copyright ©2020 Mobius Institute www.mobiusinstitute.com Page 10 CAT III key points System dynamics… Multi-degree of freedom (MDOF) systems  Students should know the definition of multi degree of freedom system (MDOF)  Students should understand the concepts of:  Modes  Nodes and anti-nodes  Bending and torsional modes  Students should be able to interpret Bodé plot and Nyquist plots associated with MDOF systems  Students should be able to determine which mode has more or less damping from a Bodé plot  Students should be aware that flexible rotors also have modes Natural frequencies and resonances Detecting and testing for resonance  Students should understand the various ways to detect resonance  Unusually high, directional peaks in the spectra with humps under them  Vibration that goes up or down significantly with changes in speed  Broken welds, leaking pipes, cracked bolts and other results of high vibration  Students should understand in detail the various tests for resonance, the graph displays and the data collector settings associated with them:  Bump test, changing speed, run up or coast down test  Averaging types, windows, gain settings, waterfall plots, Campbell diagrams, order tracking etc. Cross channel measurements  Students should understand the following cross channel data types including when and how they are used  Cross-channel phase  Transmissibility or Frequency Response Function  Coherence  Students should understand the difference between transmissibility as used in an ODS test and the FRF used in a modal test  Students should understand the data collector settings associated with these tests  Averages, windows, gain settings, trigger settings etc.  Students should be familiar with the “complete data set” and why one would want to view all of these graphs  Students should understand the causes of poor coherence [email protected] Copyright ©2020 Mobius Institute www.mobiusinstitute.com CAT III key points Page 11 ODS analysis  Students should understand the differences between ODS and modal analysis and when to use each one  Students should be aware that ODS tells us nothing about modes or natural frequencies if the machine or structure is not in resonance when it is tested  Students should understand transmissibility  Students should understand the various ODS test methods and when to use each one  Simple ODS using a tach as a phase reference  Simple graphing method  Two channel frequency based ODS  Multi-channel time based ODS  Students should understand the general methodologies associated with performing the ODS tests just listed Modal analysis  Students should understand the differences between ODS and modal analysis and when to use each one  Students should understand the modal analysis test methodology using a shaker or calibrated hammer  This includes data collector setup  This includes understanding the data being collected  Selecting hammer tips  Students should understand the FRF and coherence measurements  Students should understand the driving point measurement  Students should understand the principle of reciprocity in terms of roving hammer or roving sensor  Be aware of sensor orientation and phase references  Students should understand how modal analysis is used in conjunction with FEA Dealing with resonances Correcting resonances  Resonance occurs when a forcing frequency excites a natural frequency  To solve a resonance problem the forcing frequency should be 15-20% away from the natural frequency  You can change the forcing frequency by changing speed or by changing the number of elements such as fan blades  You can change the natural frequency by altering the mass or stiffness of the structure  Modal analysis and FEA can be used to determine how to change the structure  Don’t add stiffeners to nodal points  You can reduce the amplification at resonance by adding damping [email protected] Copyright ©2020 Mobius Institute www.mobiusinstitute.com Page 12 CAT III key points Dealing with resonances… Tuned absorbers  Tuned absorbers can be used to solve a resonance problem  The forcing frequency must remain constant  Isolation separates the forcing frequency from the natural frequency  Isolation can be achieved by design, by placing machines on separate foundations for example  Students should be familiar with the graph below from an SDOF and how it relates to isolation Rolling element bearing analysis Bearing fault conditions  Students should understand the difference between bearing care (proactively removing the root causes of bearing failure) and bearing wear (using CM technologies to detect damaged bearings)  Students should be aware of the common root causes of bearing failure  You should have some ideas of how to reduce or remove these root causes  Students should appreciate the value of the proactive approach Defect frequencies  Students should understand the concept of calculated bearing defect frequencies  Students should understand the primary defect frequencies (BPFO, BPFI, BSF and FTF) and amplitude modulation  Students should be aware that this information is available in databases and that defect frequencies can be estimated based on the number of balls or rollers  Students should understand the pros and cons of using calculated frequencies  From a program management point of view students should be aware of the problems associated with not keeping bearing information up to date or of having the wrong information [email protected] Copyright ©2020 Mobius Institute www.mobiusinstitute.com CAT III key points Page 13 Rolling element bearing analysis… High frequency techniques  Students should be aware of the high frequency techniques available for early detection of bearing wear or detection of bearing wear in low speed bearings  Students should understand the issues involved in measuring high frequencies  Sensor mounting, filters, sample rate, proximity to bearing, dynamic range etc.  Students should understand the difference between the high frequency techniques  Measuring stress waves directly, using the sensor natural frequency, demodulating any high frequency being modulated  Students should understand demodulation or enveloping  How it works  How to set up the test (filters, Fmax, LOR etc.)  How to interpret the data  Students should understand how the high frequency techniques fit in to the overall strategy of bearing wear detection Detecting bearing wear  Students should be comfortable using the techniques described in this section for detecting bearing wear, with an understanding that different indicators appear at different times in the progression of a failure  Spectra, time waveforms, high frequency tests etc.  Students should be able to choose an appropriate strategy for detecting bearing wear  Students should be able to recognize the common patterns associated with bearing wear in the various data types  Students should appreciate the difference between the proactive and predictive (condition monitoring) approaches Journal bearing analysis Journal bearings and proximity probes  Students should be aware that different bearing designs exist to deal with stability, vibration and damping issues etc.  You do not need to know the different bearing types  Be aware of thrust bearings  Students should understand the application and workings of proximity probes  Calibration and sensitivity  AC and DC components  Installation (orthogonal probes), Keyphasor etc.  Use as Keyphasor  Students should be aware of probe naming and numbering conventions  Students should be aware of the difference between prox probe measurements and casing vibration measurements  Absolute shaft vibration [email protected] Copyright ©2020 Mobius Institute www.mobiusinstitute.com Page 14 CAT III key points Journal bearing analysis… Orbit analysis and centreline analysis  Students should understand the orbit plot and the keyphasor dot in detail  Dot and gap shows direction of precession  AC Component from prox probes is used  Students should understand the difference between direct and filtered orbits  Students should understand slow roll glitch removal  Students should understand the shaft centerline plot in detail  DC component from prox probes is used  Shows average shaft position in bearing  Understand eccentricity ratio  Healthy position of shaft will depend on bearing design  Direction of rotor rotation Fault diagnosis  Students should understand the basic difference in the orbit plots for unbalance, misalignment, looseness, rubs, and oil whirl  Students should understand why you would use a centerline plot instead of an orbit plot  Students should understand what oil whirl and oil whip are  Students should understand how to recognize sub synchronous vibration in the orbit Electric motor analysis Induction and synchronous motors  Students should understand the basic components and workings of AC induction motors and synchronous motors  Students should understand basic electro magnetism and the concept of induction  Students should understand the motor poles and the relation between the number of poles and synchronous speed  Students should understand the slip frequency  Students should understand the general relationship between slip and torque Fault diagnosis  Students should be familiar with the common forcing frequencies in AC induction motors  2xLF, slip frequency, PPF, rotor bar frequency etc.  Students should be able to find the rotor bar peak in the spectrum without knowing how many bars there are  Students should understand the issues related to testing machines on VFDs  Students should be able to diagnose the common fault conditions found in AC induction motors  Note: In the exam you will be provided with the fault patterns  Students should be aware that other technologies exist for motor testing (more can be found in the condition monitoring technologies section) [email protected] Copyright ©2020 Mobius Institute www.mobiusinstitute.com CAT III key points Page 15 Pumps, fans and compressors  Students should be familiar with the common forcing frequencies in pumps, fans and compressors  Students should understand what can cause the vane or blade frequencies to go up in amplitude  Students should be aware of the difference between using vibration in the context of a condition monitoring program and using it for performance monitoring  Students should be aware of pump curves and best efficiency point (BEP)  Students should be confident in diagnosing faults in these machines including cavitation, turbulence, blade problems etc.  Using time waveforms and spectra Gearbox analysis Gear design  Students should be familiar with the common types of gears and basic gear design  Students should understand and be able to calculate the common forcing frequencies in gears  Gearmesh frequency (GMF) and shaft speeds for up to a two stage gearbox, sidebands  Gear assembly phase frequency, hunting tooth frequency, “ghost” frequency  Formulas will be provided  Students should be familiar with circular plots Vibration analysis  Students should understand the pattern associated with the gear natural frequency (Gnf) in faults that involve impacting  Students should be able to identify the gear mesh frequency and shaft rate sidebands in a spectrum  Students should be able to set up a test to analyze a certain number of shaft revolutions in the time waveform with enough detail to see each tooth mesh  Students should be able to analyze time waveforms from gearboxes to identify broken teeth, modulation etc.  Students should be aware of gears with spokes  Students should understand the value of using time synchronous averaging when analyzing gearboxes  Students should be aware that wear particle analysis (ferrography) can often provide better and earlier information about wear in a gearbox Planetary gearboxes  Students should be aware of planetary (epicyclic) gearboxes and should generally understand how they work and where they are used  Be aware of the three common configurations of these gears  Know the names of the components (sun, planet, carrier, ring)  If forcing frequency calculations are required, formulas will be provided [email protected] Copyright ©2020 Mobius Institute www.mobiusinstitute.com Page 16 CAT III key points Balancing rotating machinery Preparing for the balance job  Students should be aware of safety concerns when performing in-situ balancing  ISO standards exist to guide you  Students should understand how to prepare for a balance job  Know where and how to attach trial and balance weights  Have a scale  Be able to take a steady phase reading  Be sure the machine suffers from unbalance  Have appropriate software, etc.  Students should know what their balance goal is (more on this later) Vectors and polar plots  Students should be familiar with polar plots  Students should be familiar with vectors  A vector contains a magnitude and a phase angle  Students should be familiar with basic vector math  Understand that vectors can be added and subtracted graphically using a ruler and a protractor or mathematically using geometry  Understand how vectors are used in single-plane balancing Single-plane balancing  Students are responsible for understanding the single-plane balance in detail - (this is Category II material)  The balancing procedure  Selecting a trial weight (formulas will be provided)  The desired effect of the trial weight (30-30 rule)  Where to place the trial weight (units, phase lag, flexible rotors)  Definition of “O”, “T” and “O+T” vectors  Understand the purpose of the trim run  Determine when the rotor is balanced enough  Understand why the job might not go as planned Adding and splitting weights  Students should understand how to split weights  Students should know how to combine weights  Students should know how to remove weight if weights can’t be added and how to deal with adding weights at a different radius from the trial weight  Note - these are all Category II subjects Four run no phase balancing  Students should be familiar with four run no phase balancing  Students should understand why or when this approach might be used instead balancing with phase, which is more common  Students should understand the four run no phase balancing procedure Two-plane balancing  Students should understand when to perform a two-plane balance  Using ISO guidelines  Using phase readings  Students should understand the two-plane balance conceptually  Static and couple unbalance  Students should understand the two-plane balance methodology and procedures for regular and overhung units  You will not have to use vectors to calculate a two-plane balance solution [email protected] Copyright ©2020 Mobius Institute www.mobiusinstitute.com CAT III key points Page 17 Balancing rotating machinery… Balancing machines with flexible rotors  Students should simply be aware that balancing flexible rotors requires knowledge of their mode shapes  Flexing of the motor must be reduced  The axial position of the balance weights matters as it effects how (and if) you balance it  Flexible rotors are covered in Category IV ISO and ANSI balance standards  Students should understand that balance standards can be based on residual unbalance, 1x vibration amplitude or both  Students should understand why both of these criteria are important and why one criteria might be more important than the other in certain situations  Students should understand how to calculate residual unbalance  Students should be aware that a variety of balance standards exist  You should know which are used in your plant or be able to recommend a standard if none are being used  Students should be able to use and interpret all of the charts included in this section  Charts will be included with the exam if needed Shaft alignment  Students should understand the importance of precision alignment  Students should be aware of pre alignment checks and procedures to ensure the job goes safely and successfully  Students should understand alignment tolerances for angle and offset  Be aware of thermal expansion  Be aware of dynamic shaft movement  Be familiar with issues related to using dial indictors including bar sag  Recognize rim face and reverse dial methods  Understand the importance of dealing with soft foot and pipe strain  Understand base bound and bolt bound  Be familiar with alignment procedure Generating alarms with statistics  The Category III analyst is responsible for managing the vibration program  This includes setting criteria for alarms  Includes making sure the program is run in an efficient manner  Statistical alarms are a good solution to both  You may also be responsible (in real life) for selecting a monitoring system or software package so you should understand the capabilities of such systems to see if they will meet your needs  You should understand how the various alarms work (masks, bands etc.) [email protected] Copyright ©2020 Mobius Institute www.mobiusinstitute.com This page left intentionally blank