1. Introduction. A vibration FFT (Fast Fourier Transform) spectrum is an incredibly useful tool for machinery vibration analysis. If a machinery problem exists. Vibration Spectrum Analysis for Indicating Damage on Turbine and Steam Generator Amurang Unit 1. Article (PDF Available) · December Vibration Analysis Techniques 4. Definitions. 3. 2. Level Measurement. 3. 3. Time Waveform. FFT Spectrum and Phase Analysis.
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always relative to the vibration level of a “good”;. “new” machine! DETECTION VS . ANALYSIS. VIBRATION. (AMPLITUDE VS. FREQUENCY). Overview / How To. However, the basic processes of measurement and analysis have remained . Frequency analysis is the essence of vibration analysis and enables the. 5. Time Waveform Analysis complex time waveform. Individual vibration signals combine to form a complex time waveform showing overall vibration frequency.
For example, some components have a Thus, vibration has three measurable characteristics: Although these three for most machines, but is normal for them.
The current reading characteristics are related mathematically, they are three by itself might lead an analyst to believe that a problem exists, different characteristics, not three names for the same quantity. It is necessary to select a vibration measurement and sensor type that measures the vibration most likely to reveal the expected ISO Standards are good for a start until you develop a machine failure characteristics.
Jaw crusher vibration analysis pdf
Vibration is exampled using a spring-mass setup. Measured in mils or micrometers, displacement is the change in distance or position of an object relative to a reference.
Displacement is typically measured with a sensor commonly known as a displacement probe or eddy probe. A displacement probe is a non-contact device that measures the relative distance between two surfaces. Displacement probes most often monitor shaft vibration and are commonly used on machines with fluid film bearings.
Displacement probes measure only the motion of the shaft or rotor relative to the casing of the machine. This relationship is used for balancing and shaft orbital analysis reference the Phase Section.
It is the most common machine vibration measurement. Historically the velocity sensor was one of the first electrical sensors used for machine condition monitoring. This because for an equal amount of dynamic motion being generated, velocity remains constant regardless of frequency. However, at very low frequencies under 10 Hz velocity sensors lose their effectiveness.
Likewise at higher frequencies above 2 kHz.
Today, with the arrival of low cost The above time waveform plot illustrates how the signal from an and versatile accelerometers, most velocity values are obtained accelerometer or velocity probe appears when graphed as by integrating an acceleration reading into the velocity domain.
This type of vibration plot is also called a time domain plot or graph. Vibration in terms vibration. Though typically not as useful as other analysis of acceleration is measured with accelerometers. An formats, time waveform analysis can provide clues to machine accelerometer usually contains one or more piezoelectric crystal condition that are not always evident in the frequency spectrum elements and a mass. In non-mathematical terms, this means that the signal is Base Connector broken down into specific amplitudes at various component frequencies.
When the piezoelectric crystal is stressed it produces an electrical output proportional to acceleration. The crystal is stressed by the mass when the mass is vibrated by the component to which they are attached. Accelerometers are rugged devices that operate in a very wide frequency range from almost zero to well above kHz. However, since velocity is the most common measurement for monitoring vibration, acceleration Frequency scale showing measurements are usually integrated either in the accelerometer component vibration signals itself or by the data collector to get velocity.
Acceleration units at various frequencies. However, this vibration signal is of such low frequency contained in the signal.
These values or amplitudes energy that, with overall vibration monitoring, it is lost in the are then plotted over the frequency scale. The resulting plot is called an FFT spectrum. Spall An FFT spectrum is an incredibly useful tool. Following are a examples of alternate processing methods. For that matter, SEE measurements are also very effective for measuring any machine condition that produces acoustic emissions such as corrosion and SEE technology Spectral Emitted Energy provides very early friction due to fretting, cavitation, sliding or friction events, etc.
SEE detection specific conditions. Circumstances that can cause acoustic provides enough pre-warning for the maintenance person to emissions include: See Appendix A for a more detailed description of measuring phase. This type of signal is not considered HFD vibration as much as it is considered high frequency sound, however, vibration is the commonly used industrial term.
HFD provides early warning of bearing problems. The High Frequency Detection HFD processing method displays a numerical overall value for high frequency vibration generated by small flaws occurring within a high frequency band pass 5 kHz to 60 kHz.
One competitors technology is very similar to HFD and gives These technologies enhance the repetitive components of a the same indications. Measured as Vibration Turn off machine power and monitor vibration. If the vibration immediately drops, the problem is electrical.
Vibration Analyzer / Vibration Analyser
On an overhung machine, imbalance and Note: Unsatisfactory — Unacceptable Levels. Use phase measurements to differentiate between the two.
Radial 1 and Radial 2 positions differ by 90 Note: No radial Displacement phase shift across the machine or coupling. Account Radial Displacement for change in sensor orientation when making axial measurements. Bearing defect SEE frequencies are non- integer multiples of running speed i.
In other words, what are the possibilities? When adjacent machine. Vibration from one machine can measuring displacement, velocity, or acceleration travel through the foundation or structure and affect vibration, all data collectors should produce very similar vibration levels on an adjacent machine. Electric motors usually run at these speeds. As mentioned earlier, an FFT spectrum is an incredibly useful analysis tool. Look for this peak and check for peaks at two until the problem becomes critical.
Harmonics FFT spectra allow us to analyze vibration amplitudes at various usually cause vibrations at multiples of the running component frequencies on the FFT spectrum. In this way we speed frequency although they might be very small.
Certain information is needed before attempting to diagnose an FFT spectrum. Most experts agree that over half of all machinery problems are caused by misalignment.
The two types analyze the spectrum. Analysis usually follows a process of of misalignment are angular and parallel, or a combination of elimination. Eliminate what is not on the spectrum and what is both. Try to find out if they are electrical or mechanical. These peaks may or may not represent the indicated fault. Look for harmonics to determine if the identified frequencies were generated from the indicated fault.
Parallel misalignment occurs when the shaft centerlines are parallel but displaced from one another. Possible causes of misalignment are: Most machines are aligned times the fundamental fault frequency, then this also cold, then as they operate and heat up, thermal growth represents a strong indication that the indicated fault is causes them to grow misaligned.
A higher than normal reading than its design specification, which in turn causes bearing failure indicates a problem. If possible, measure the phase shift between axial readings on opposite ends of the machine. With static imbalance only one force is involved. The term direction compared to the radial direction. Misalignment forces are seldom the same in both positions.
If higher than normal forces are present in the vertical plane, misalignment is indicated. In reality, almost all imbalance is dynamic imbalance.
A response spectrum method for random vibration analysis of mdf systems
Dynamic imbalance is the combination of static and couple imbalance. If the axial 1x amplitude is abnormally high, On simple machines, there is usually more static imbalance than and there is a coupling or belt, couple imbalance.
Both uniform and non-uniform BTT vibration signals are collected, and reconstructed order analysis are carried out. Simulation and experimental results testify that the proposed algorithms can accurately capture characteristic high EOs of synchronous and asynchronous vibrations under VRS by using few BTT sensors.
The significance of this paper is to overcome the limitation of conventional BTT methods of dealing with variable blade rotating speeds. Keywords: vibration monitoring, multiple blade tip-timing sensors, variable rotation speeds, angular sampling, reconstructed order analysis 1. Introduction High-speed blades are key mechanical rotating components in turbo-machinery, such as engine compressor and turbine blades. High cycle fatigue due to low stress and high-frequency vibrations cause different kinds of blade damage or even catastrophic faults.
Thus, on-line vibration monitoring of high-speed blades is urgent from the viewpoints of safety, reliability, availability, and maintenance [ 2 ]. As blades rotate continuously during operating, it is difficult to carry out on-line vibration monitoring. Currently, there are two classes of methods, namely contact and non-contact monitoring. For contact vibration monitoring, strain gauges are mounted on a blade surface, and signals are sampled by using a slip-ring [ 3 ].
This class of method has several intrinsic drawbacks. First, we need to use at least a strain gauge to monitor each blade. This results in numerous strain gauges being used for monitoring the whole engine. Strain gauges themselves may affect the vibration characteristics of a blade.
Second, the lifespan of a strain gauge is limited due to the challenging operational environments, so they need to be replaced regularly, and the cost is high.
Third, a high-speed slip ring is needed to transmit signals of all strain gauges, the expense of which is also very high. To overcome these shortcomings, non-contact blade vibration monitoring methods have arisen in recent years, such as laser Doppler vibrometry LDV [ 4 ].
Stationary LDV measurement can be used to detect all the blades as they pass in front of the sensor through non-harmonic Fourier analysis [ 5 , 6 , 7 ]. Recently, blade tip-timing BTT has become another promising non-contact measurement approach [ 8 , 9 ]. BTT uses the times at which the blade tips pass the casing-mounted probes to obtain all-blade vibrations simultaneously. A review of BTT vibration analysis methods can be found in References [ 10 , 11 ].
Detectors are used in an attempt to adequately map the correct signal power to the appropriate frequency point on the display. There are in general three types of detectors: sample, peak, and average Sample detection — sample detection simply uses the midpoint of a given interval as the display point value. While this method does represent random noise well, it does not always capture all sinusoidal signals. Peak detection — peak detection uses the maximum measured point within a given interval as the display point value.
This insures that the maximum sinusoid is measured within the interval; however, smaller sinusoids within the interval may not be measured. Also, peak detection does not give a good representation of random noise.
Average detection — average detection uses all of the data points within the interval to consider the display point value.
This is done by power rms averaging, voltage averaging, or log-power averaging. This can either be with a specific resolution bandwidth e. This is also called the sensitivity of the spectrum analyzer. To increase the sensitivity of the spectrum analyzer a preamplifier with lower noise figure may be connected at the input of the spectrum analyzer.
For example, in RF mixers, spectrum analyzer is used to find the levels of third order inter-modulation products and conversion loss. In RF oscillators, spectrum analyzer is used to find the levels of different harmonics.
In telecommunications , spectrum analyzers are used to determine occupied bandwidth and track interference sources.Certain information is needed before attempting to diagnose an FFT spectrum. If both the above conditions are true, the problem is probably a bent shaft. The heavy spot rotates 90 degrees to the sensor position.
This pulse initiates data collection. A sensitive photodiode embedded in the cavity provides an intensity signal, which is plotted against the ramp voltage to produce a visual representation of the optical power spectrum.
Sensor — A transducer which motion; may be expressed Probe Gap — The physical senses and converts a as acceleration, velocity, or Orbit — The path of shaft distance between the face physical phenomenon to an displacement.
The terms of voltage peaks centered around a a signal as a function of frequency range that the millivolts , which is the major peak. Try to find out if they are electrical or mechanical. This assumption is impractical, and blade damages are always formed and accumulated during variable operational conditions. No radial Displacement phase shift across the machine or coupling.
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