Vibration analysis pdf

 

    PDF | On Jun 1, , Jaafar Alsalaet and others published Vibration Analysis and Diagnostic Guide. Breakdown. ➢ Preventive. ➢ Predictive. ➢ Reliability centered (Proactive). Vibration analysis. ➢ What is machine vibration. ➢ Measuring and analyzing vibration. 1. Introduction. A vibration FFT (Fast Fourier Transform) spectrum is an incredibly useful tool for machinery vibration analysis. If a machinery problem exists.

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    Vibration Analysis Pdf

    Industrial vibration analysis is a measurement tool used to identify, predict, and prevent failures in rotating machinery. Implementing vibration analysis on the. measurements to quantify the symptoms, and then analysis to interpret the data. It is usually This means having a vibration analyzer at one's disposal. More on. Practical Machinery Vibration Analysis and Predictive Maintenance vi Contents Other titles in the series Practical Data Acquisition for Instrumentation and.

    Get Price Crushing Resource Book - Metallurgist Crushing or Impact Work Indices are measured in the laboratory using a special Vibration monitoring installed on the crusher to provide information to the Below is a summary of the conveyors used within the SDGM crushing circuit;. The manual wedge setting adjustment is faster and safer than outdated shim system analysis, field repairs. This helps minimize the vibration transferred to the supporting. Get Price heavy-duty jaw crushers - Global Crushers Dynamically balanced flywheels reduce vibration on either portable plant or type jaw crusher that does not rely upon gravity alone to move material through stress analysis is preformed using finite element analysis techniques along with Get Price Coal Mining Equipment Vibration Analysis Sept 3, Sep 3, A. Vibration Limits: Prior to beginning vibration analysis of coal mining equipment , a review was made of The crushers handle lump coal and oversize rock, crushing 4. Our diagnostic experts have. Get Price arto ahlsten condition monitoring appliions of crushing plant Oct 5, bearing of the crusher and monitoring vibration of machine's main conveyor. The used..

    The installation of an accelerometer must carefully be considered for an accurate and reliable measurement. Accelerometers are designed for mounting on machine cases.

    This can provide continuous or periodic sensing of absolute case motion vibration relative to free space in terms of acceleration. Inertial measurement devices measure motion relative to a mass.

    Accelerometers consist of a piezoelectric crystal made of ferroelectric materials like lead zirconate titanate and barium titanate and a small mass normally enclosed in a protective metal case. When the accelerometer is subjected to vibration, the mass exerts a varying force on the piezoelectric crystal, which is directly proportional to the vibratory acceleration.

    The charge produced by the piezoelectric crystal is proportional to the varying vibratory force. Some sensors have an internal charge amplifier, while others have an external charge amplifier. Current or voltage mode This type of accelerometer has an internal, low-output impedance amplifier and requires an external power source.

    The external power source can be either a constant current source or a regulated voltage source. This type of accelerometer is normally a two-wire transducer with one wire for the power and signal, and the second wire for common. They have a lower-temperature rating due to the internal amplifier circuitry. Output cable lengths up to feet have a negligible effect on the signal quality.

    Longer cable lengths will reduce the effective frequency response range. Charge mode Charge mode accelerometers differ slightly from current or voltage mode types. These sensors have no internal amplifier and therefore have a higher-temperature rating. An external charge amplifier is supplied with a special adaptor cable, which is matched to the accelerometer.

    Vibration Analysis of Rotors | SpringerLink

    Field wiring is terminated to the external charge amplifier. As with current or voltage mode accelerometers, signal cable lengths up to feet have negligible effect on the output signal quality. Mounting It is important to know the possible mounting methods for this vibration sensor. Four primary methods are used for attaching sensors to monitoring locations.

    These are stud mounted, adhesive mounted, magnet double leg or flat mounted and non-mounted — e. Each method affects the high-frequency response of the accelerometer. Stud mounting provides the widest frequency response and the most secure, reliable attachment. The other three methods reduce the upper frequency range of the sensor. In these cases, the sensor does not have a very secure direct contact with the measurement point. Inserting mounting pieces, such as adhesive pads, magnets or probe tips, introduces a mounted resonance.

    This mounted resonance is lower than the natural resonance of the sensor and reduces the upper frequency range. A large mounting piece causes lower mounted resonance and also lowers the usable frequency range of the transducer. This method is accomplished by screwing the sensor in a stud or a machined block. This method permits the transducer to measure vibration in the most ideal manner and should be used wherever possible.

    The mounting location for the accelerometer should be clean and paint-free. The mounting surface should be spot-faced to achieve a smooth surface. The spot-faced diameter should be slightly larger than the accelerometer diameter. Any irregularities in the mounting surface preparation will translate into improper measurements or damage to the accelerometer.

    The adhesive or glue mounting method provides a secure attachment without extensive machining. However, when the accelerometer is glued, it typically reduces the operational frequency response range or the accuracy of the measurement.

    This reduction is due to the damping qualities of the adhesive. Also, replacement or removal of the accelerometer is more difficult than with any other attachment method.

    For proper adhesive bonding, surface cleanliness is of extreme importance.

    The magnetic mounting method is typically used for temporary measurements with a portable data collector or analyzer. This method is not recommended for permanent monitoring. The transducer may be inadvertently moved and the multiple surfaces and materials of the magnet may interfere with high-frequency signals.

    By design, accelerometers have a natural resonance which is 3—5 times higher than the high end of the rated frequency response. The frequency response range is limited in order to provide a flat response over a given range.

    The rated range is achievable only through stud mounting. As mentioned before, any other mounting method adversely affects the resonance of the sensor, such as the reliable usable frequency range.

    Other types of accelerometers with a wide range of sensitivities for special applications such as structural analysis, geophysical measurement, very high frequency analysis or very low speed machines are also available.

    Frequency range Accelerometers are designed to measure vibration over a given frequency range. Once the particular frequency range of interest for a machine is known, an accelerometer can be selected. Typically, an accelerometer for measuring machine vibrations will have a frequency range from 1 or 2 Hz to 8 or 10 kHz.

    Accelerometers with higher-frequency ranges are also available. Calibration Piezoelectric accelerometers cannot be recalibrated or adjusted. Unlike a velocity pickup, this transducer has no moving parts subject to fatigue. Therefore, the output sensitivity does not require periodic adjustments.

    However, high temperatures and shock can damage the internal components of an accelerometer. At the same time, the power supply should also be checked to eliminate the possibility of improper power voltage affecting the bias voltage level of the sensor.

    Typical applications are predominantly high-speed turbomachinery. Eddy current transducers are the only transducers that provide displacement of shaft or shaft-relative shaft relative to the bearing vibration measurements. This is sent through the extension cable and radiated from the probe tip. In this way, an Eddy current transducer can be used for both radial vibration and distance measurements such as the axial thrust position and shaft position.

    Number of transducers All vibration transducers measure motion in their mounted plane. In other words, shaft motion is either directed away from or towards the mounted Eddy current probe, and thus the radial vibration is measured in this way. Therefore, the Eddy current probe should be mounted in the plane where the largest vibrations are expected.

    On larger, more critical machines, two Eddy current transducer systems are normally recommended per bearing. If possible, the orientation of the transducers should be consistent along the length of the machine train for easier diagnostics. In all cases, the orientations should be well documented. Perpendicular to shaft centerline Care must be exercised in all installations to ensure that the Eddy current probes are mounted perpendicular to the shaft centerline.

    Clearance must be provided on all sides of the probe tip to prevent interference with the RF field. For instance, if a hole is drilled in a bearing for probe installation, it must be counter-bored to prevent side clearance interference.

    It is important to ensure that collars or shoulders on the shaft do not thermally grow under the probe tip as the shaft expands due to heat.

    Internal mounting During internal mounting, the Eddy current probes are mounted inside the machine or bearing housing with a special bracket Figure 3. The transducer system is installed and gapped properly prior to the bearing cover being reinstalled. This can be accomplished by using an existing plug or fitting, or by drilling and tapping a hole above the oil line. For added safety and reliability, all fasteners inside the bearing housing should be safety wired.

    Advantages of internal mounting Less machining required for installation. True bearing-relative measurement is possible. The Eddy probe has an unconstrained view on the shaft surface. Disadvantages of internal mounting There is no access to probe while the machine is running. Transducer cable exits must be provided. Care must be taken to avoid oil leakage.

    These adaptors allow external access to the probe, but the probe tip itself is inside the machine or bearing housing. While drilling and tapping the bearing housing or cover, it is important to ensure that the Eddy probes are installed perpendicular to the shaft centerline.

    Eddy probe has an unconstrained view on the shaft. Gap may be changed while machine is running. More machining required. The construction of older machines may not provide ideal installation of probes. External Eddy probes are mounted on such machines Figure 3. It is usually a last resort installation.

    Special care must be given to the Eddy probe viewing area, and mechanical protection must be provided to the transducer and cable. Advantages of external mounting It is the most inexpensive installation.

    Requires mechanical protection. Because Eddy currents are sensitive to the permeability and resistivity of the shaft material, any shaft material other than series steels must be specified at the time of order.

    In the case of another kind of shaft material, the probe supplier might require a sample of the shaft material. Mechanical runout Eddy current transducers are also sensitive to the shaft smoothness for radial vibration.

    The selected journal area on most shafts is wider than the bearing itself, allowing for probe installation directly adjacent to the bearing.

    Electrical runout Since Eddy current transducers are sensitive to the permeability and resistivity of the target material and also because the field of the transducer extends into the surface area of the shaft by approximately 0. Another form of electrical runout can be caused by small magnetic fields, such as those left by magna-fluxing without proper degaussing.

    The probe is installed in the tester with the target set against the probe tip. The micrometer with the target attached is then rotated away from the probe in increments of 0. The voltage reading is recorded and plotted at each increment.

    The graph obtained for the specified range should be linear. Probe to target gap When installed, Eddy current probes must be gapped properly. In most radial vibration applications, adjusting the gap of the transducer to the center of the linear range is adequate. For example, as shown in Figure 3. In all cases, final probe gap voltage should be documented and kept in a safe place. This voltage setting will place the probe in the middle of its linear range, thus allowing the probe to sense movement in the positive direction and in the negative direction.

    Proximity probes should be located at the bearing, and no further than 25 mm or one inch axially from the bearing towards the center of the shaft.

    However, this signal in the raw form is of no use unless it is processed to provide meaningful information that can be related to machine condition. Thus, there is a need for monitoring equipment that can take such an electrical signal from a transducer and process it into meaningful data.

    Also, in the earlier topics, we have discussed the adoption of various maintenance philosophies applied in process plants or on the shop floor, based on the equipment classification. The type of monitoring methods to be used for each different machine is also based on the above rationale.

    Once the machinery monitoring needs are established, the next step is to select suitable monitoring equipment that fulfills these requirements the best. Plant operators and vibration technicians carry handheld meters and analyzers on their routine rounds. When these are held in contact with machinery, they provide a display of vibration levels either analog or digital.

    The readout provides immediate information that can be used to determine if the overall vibration levels are normal or abnormal.

    Handheld vibration meters are typically battery powered and use an accelerometer for sensing. Sometimes a velocity pickup is used. They are small, lightweight and rugged for day-to-day use Figure 3. Handheld meters can provide the following data depending on the specific model: Advantages They are convenient and flexible, and require very little skill to use.

    It is an inexpensive starting point for any new condition-monitoring program. Disadvantages Limited in the type of measurements that they can perform. They also lack data storage capability however, some instruments are now available with some limited storage capacity. This data acquisition method is rapid, convenient and demands minimal skills. The first step is to identify the positions on the machine from where measurements should be taken.

    Mechanical vibrations have an analogy to an electrical current. Just as an electric current would tend to go to earth, vibrations caused by defects in rotating machinery would travel to the ground through its supports.

    Thus, it is at the bearings where the best signals for condition monitoring can be measured and hence these are generally the best positions for vibration measurements. It is always necessary to follow a convention for labeling the various bearings of a machine train from where measurements were made.

    The general convention is to start labeling from where the power comes in. For example, a simple machine train consisting of a motor and pump will be labeled in the following manner Figure 3. Once the bearings are labeled, it is important that vibrations are taken in the three Cartesian directions. In vibration nomenclature, these are the vertical, horizontal and axial directions. This is necessary due to the construction of machines — their defects can show up in any of the three directions and hence each should be measured.

    It is thus important that personnel carrying out this task are aware of the possible errors that can occur while taking measurements. Errors can occur due to: Position on machinery Measurements should be taken at exactly the same location to enable direct comparisons of data sets. Moving the probe only a small distance on a machine can produce drastically different vibration levels.

    ACOUSTIC AND VIBRATION CALIBRATION

    To ensure measurements are taken at the same spot, it should be marked with paint, or a shallow conical hole should be drilled for identification. Probe angle The sensor or the probe should always be oriented perpendicular to the machine surface.

    Tilting the probe slightly at an angle may induce an error. Probe type Some handheld meters are supplied with probes called stingers and also round magnets, which can be screwed into velocity transducers or accelerometers. Measuring vibration with magnetic attachments can collect higher vibration frequencies than what can be measured with handheld probes.

    When collecting vibration data on a machine generating high frequencies with a handheld meter, changing the probe type will show a drastic difference in the overall levels. Pressure Even and consistent pressure of the hand is required to get comparable readings with handheld meters.

    There are basically two types of data collectors and analyzers Figure 3. Provides orderly collection of data. Automatically reports measurements out of pre-established limit thresholds.

    Can perform field vibration analysis. Disadvantages They are relatively expensive. Operator must be trained for use. Limited memory capability and thus data must be downloaded after collection. Therefore, the data must be downloaded to the computer to form a history and long-term machinery information database for comparison and trending. To perform the above tasks, and also aid in collection, management and analysis of machinery data, database management software packages are required.

    These database management programs for machinery maintenance store vibration data and make comparisons between current measurements, past measurements and pre- defined alarm limits. Measurements transferred to the vibration analysis software are rapidly investigated for deviations from normal conditions.

    Overall vibration levels, FFTs, time waveforms and other parameters are produced to help analyze these vibration changes. Reports can be generated showing machines whose vibration levels cross alarm thresholds. Current data are compared to baseline data for analysis and also trended to show vibration changes over a period of time.

    Trend plots give early warnings of possible defects and are used to schedule the best time to repair Figure 3. In addition, the software helps to determine a route for data collection. The positions from where data should be collected can be configured to form an efficient sequence. This sequence or route is then downloaded to the data collector and can then help the operator in the field to determine which measurement position should be taken next. This ensures that all the necessary data are collected in the least possible time and in the same sequence every time.

    Advantages They aid in data collection, management and analysis of machinery data. They can save long-term machinery data that help to compare present and past condition-monitoring data. They assist in vibration analysis. They provide user-friendly reports. They must be configured for individual requirements. A lot of information is required as initial input.

    Currently there are efforts to resolve this, but up to date it remains a problem. Here sensors e. Eddy current probes installed in turbomachinery are permanently installed on the machines at suitable measurement positions and connected to the online data acquisition and analysis equipment.

    The vibration data are taken automatically for each position and the analysis can be displayed on local monitoring equipment, or can be transferred to a host computer installed with database management software.

    Because monitoring equipment are permanently connected to the sensors, intervals between measurements can be short and can be considered as continuous. This ability provides early detection of faults and supplies protective action on critical machinery.

    Protective action taken by online data acquisition and analysis equipment is in the form of providing alarms to warn the operators of an abnormal situation Figure 3. In cases of serious faults, this protective action can shut down machines automatically to prevent catastrophic failures. Transferring the information to a host computer with database management software enhances the convenience and the power of online data acquisition. Bently Nevada — Machinery Asset Management software brochure connect multiple local monitoring units that can send data from different machines to a central host computer.

    Thus, machines at various physical locations can be monitored from one location. Also, information can be transferred from the host computer to the local monitoring unit for remote control see Figure 3.

    Advantages Performs continuous, online monitoring of critical machinery. Measurements are taken automatically without human interference.

    Provides almost instantaneous detection of defects. Disadvantages Reliability of online systems must be at the same level as the machines they monitor. Failure can prove to be very expensive. Installation and analysis require special skills. These are expensive systems.

    After assessing the information, the software can provide a diagnosis of possible problems in a machine, the severity of the problem and can even recommend actions that can alleviate the detected problem. Bently Nevada — Machinery Asset Management software brochure Often called expert systems, these systems require information of the machine being analyzed and its characteristics in order to build a mathematical model of the machine.

    The model is then stored and used by the expert system to analyze current data and predict a pending problem. The system studies the symptoms of the machine and makes recommendations in order of confidence factors with respect to the severity of the problem.

    Data acquisition 47 Expert systems analyze current data and compare it with historical data to search for any changes.

    Structural vibration analysis

    The systems then assess the severity of significant changes using absolute thresholds, statistical limits and the rate of change in the calculations.

    A series of proven rules are then applied to the data. Finally, all rule violations are combined to produce a probability that the diagnosis is correct. A very important aspect of the vibration wave, next to its amplitude and frequency, is the phase relationships.

    In vibration analysis, the phase difference between two different waveforms is utilized for many different applications, for example machinery defect diagnosis.

    Phase can be measured in many ways, and some are discussed below. It should be noted that in vibration analysis, phase measurement instruments are used in conjunction with the analyzers.

    The analyzer picks up the vibration waveform, and the following instruments can provide phase and rpm information: Stroboscopes Stroboscopes are normally a part of the accessories kit supplied with a vibration analyzer, but they are available as separate instruments as well.

    Stroboscopes have a high-intensity light that is flashed at a certain frequency, triggered internally or by the vibration analyzer.

    It provides a visual method for observing phase differences Figure 3. Monarch Stroboscopes To obtain a phase difference reading, a reference mark is made on the rotor. A keyway or a notch that can be easily viewed is also a good reference. This makes phase readings with the smallest error possible. This angular position is then recorded. The reference mark will now, depending on the situation, appear stationary at the same or some other angular position. This reading is also recorded.

    The phase difference between the two positions on the machine where the vibration probes were placed is given by the difference of the angular positions of the reference marks as observed with the strobe. In some cases, only a portion of the shaft may be visible, as just a side view from the coupling guard. In cases where only half of the shaft circumference is visible, a single reference may be inadequate, especially when the reference mark is on the hidden side. It should be stated that this method is only reliable for general phase comparisons because it is a visual method and thus approximate.

    For a more accurate phase reading, a tape marked with angular degrees is applied around the circumference of the shaft. However, even this is a bit cumbersome when the shaft diameter is small.

    Advantages Stroboscopes are lightweight, easy to use and portable.

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    They can be used individually to measure rpm, by using an internal trigger to make the shaft appear stationary. The frequency of the trigger is the same as the rotational speed of the shaft. Some strobes can act as external triggers just like photocells, laser tachometers or keyphasors. Disadvantages Machines that do not have a reference notch or keyway must be stopped to provide one. This may be difficult in continuous process plants.

    This is a problem even with sub-harmonics and higher harmonic vibrations. It is rather difficult to obtain accurate phase readings in degrees. Extreme caution is required to use strobes in hazardous areas. To read the phase, one has to be in close proximity of the machine.

    Dual channel analyzers A single channel analyzer can only accept an input from one accelerometer at a time, whereas a dual channel instrument Figure 3. Thus, two vibration waveforms can be collected from a machine and analyzed. As we shall see later, this can provide very meaningful vibration data. Advantages The biggest advantage is that there is no need for reference marks on the shaft. As a result, there is no need to shut down the machine to provide the marks.

    The phase differences obtained are very accurate. It can provide phase differences at any frequency. Data acquisition 49 Figure 3. Photocell Whenever accurate or remote readouts of phase are required, a photocell detector, an electromagnetic or non-contact pickup may be used.

    These are usually installed within close proximity of the shaft Figure 3. As with stroboscopes, a reference mark on the shaft must be provided to trigger these pickups.

    A photocell detector responds to the reflectivity of the target. One very common way is to wrap the shaft with a black tape e. The objective is to provide an abrupt change in reflectivity of the target area of the photocell during each revolution of the shaft.

    A steady light source, rather than a strobo- scopic light source, is transmitted from the device. A photo detector or photocell produces a pulse each time light is reflected from a reflective surface on the rotating shaft the reflective tape. All phase measurements are made relative to the reflective tape, which is treated as zero degrees. Since the reflected light produces one pulse per revolution, the shaft rotation rate can also be determined easily Figure 3.

    A temporary method is to attach a key around the shaft with a high-strength tape to hold the key in place. This is not recommended for high-speed shafts. In an electromagnet pickup sensor Figure 3. This output voltage pulse change is then compared with the occurrence of maximum vibration amplitude to determine the phase difference at different locations. The photocell and keyphasor cannot indicate phase readings on their own. They must transmit their data to an analyzer or oscilloscope for analysis.

    A reference signal at the desired frequency is required to achieve this. Data acquisition 51 Where sub-multiple or non-harmonic-related vibration frequencies must be compared, a reference vibration pickup and a reference vibration analyzer with a tuneable filter can be used to provide a reference signal at any desired frequency of vibration. Every mechanical system that rotates and transmits power is subject to some kind of torsional behavior. The three important kinds of torsional behavior that are mostly referred to for analyses are: Changes in revolution 2.

    Torsional vibration 3. Transmission error. Torsional vibrometers to measure the above-mentioned phenomena are also described briefly below. The rate at which it rotates is called the angular velocity. Most of us believe that it occurs almost uniformly. However, this is not the case in many situations. Let us assume the shaft speed is 1 rpm.

    If the angular velocity is uniform, then each sector should be covered in 15 s exactly. Instead, say the first sector is covered in 10 s, the next in 20 s; the third is covered again in 10 s and the final section in 20 s. Thus, in one cycle the angular velocity increases and decreases, giving rise to what is known as changes in revolution. To measure this change in revolution, a high-resolution rotary encoder is used.

    The output signal from the encoder is converted from frequency to voltage F—V at high speeds, pulse by pulse, to determine the changes in each revolution Figure 3. Select two collinear points on the circumference of a stationary shaft. When the shaft begins to transmit power, it can twist and then there is no longer a straight line joining the two points. This line could then be slanted or spiral in shape Figure 3.

    Normally, a pair of electromagnetic revolution sensors is used for this measurement. The vibrometer measures the torsion that develops between the driving and load sides of the shaft as torsional phase difference. The phase difference obtained is F—V frequency to voltage converted at high speeds and processed using frequency calculations to determine the torsional vibration.

    A transmission error is the lead or lag in the rotational angle at the upstream and downstream locations of a power transmission unit. This is measured with the phase difference between the upstream and downstream locations of a power transmission in a manner similar to the detection of torsional vibration as discussed earlier. The per-pitch transmission error is determined from the phase difference, and then processed by frequency calculations to determine the transmission error Figure 3.

    In a multi-shaft system where gears, belts and chains are interconnected, torsional vibrations can occur due to transfer error resulting from poor machining accuracy, a deformity in the power transmissions or a change in the revolution of the rotating parts. Normally, revolution changes, torsional vibration and transmission errors are intermingled in a complex manner.

    A variety of adverse effects develop in systems which experience these changes, such as: Thus, in any rotating system comprising of rotating parts and power transmissions, it is important to measure these three parameters: The FFT analyzer built into the main unit enables frequency analysis tracking analysis and printing of analysis results in the field. Ono Sokki, Japan Technical Report, website In the torsional vibration schematics shown before, assume that it is not possible to measure the relative displacement between two points.

    Transformation of the electrical signal to its components by the analyzers, and information and documentation related to vibration data form a part of the signal processing. The processing of these signals is the basis of study in the next topic. After processing the signals, analyzers can give an output of more meaningful data that can be correlated with defects arising in machines or their components. Vibration transducers convert this motion into an electrical signal. The electrical signal is then passed on to data collectors or analyzers.

    The analyzers then process this signal to give the FFTs and other parameters. We will take a brief look at the processing of the signals, which finally provide us with the necessary information for condition monitoring. To achieve the final relevant output, the signal is processed with the following steps: Before we can discuss the above-mentioned digital signal processing steps, we need to take note of a few more terms and concepts.

    Time domain consists of amplitude that varies with time. This is commonly referred to as filter-out or overall reading. Frequency domain is the domain where amplitudes are shown as series of sine and cosine waves.

    These waves have a magnitude and a phase, which vary with frequency. The measured vibrations are always in analog form time domain , and need to be transformed to the frequency domain. This is the purpose of the fast Fourier transform FFT. The FFT is thus a calculation on a sampled signal. If FFT is a calculation on a sampled signal, the first question that arises is: Thus, the collected discrete sampled data points digital are used to reconstruct the wave, which was originally in an analog form.

    If the reconstructed digital wave has to look similar to the original wave, how fast should we record the amplitude, or in other words, take samples so that the digitized wave is an exact replica of the original analog wave?

    The answer lies in the Nyquist sampling theorem, which states: We can see that four sample intervals collected in 3 ms will result in a reconstructed wave dotted as shown in the figure. This wave is of a lower frequency and not at all a true representation of the actual wave.

    This phenomenon of formation of a lower-frequency wave due to undersampling is called aliasing. In theory, there should be no vibrations with frequencies of more than half of this sampling rate. However, this can never be ensured in practice. Therefore all analyzers are fitted with anti-aliasing filters. These are low-pass electronic filters, which allow low frequencies to pass but block higher ones. The filters remove all vibrations in the analog signal that have frequencies greater than half the sampling rate.

    These filters are automatically tuned to the proper values as the sampling frequency is changed this occurs when the frequency range of the analyzer is changed by the user. It is very important to note that filtering has to occur before digitisation of the analog commences.

    Signal processing, applications and representations 57 Figure 4. Analog signals must be converted to digital values for further processing. Figure 4. It is thus possible to collect a signal with large and small amplitudes accurately. Windowing is the equivalent of multiplying the signal sample by a window function of the same length. The manual wedge setting adjustment is faster and safer than outdated shim system analysis, field repairs.

    This helps minimize the vibration transferred to the supporting. Get Price heavy-duty jaw crushers - Global Crushers Dynamically balanced flywheels reduce vibration on either portable plant or type jaw crusher that does not rely upon gravity alone to move material through stress analysis is preformed using finite element analysis techniques along with Get Price Coal Mining Equipment Vibration Analysis Sept 3, Sep 3, A.

    Vibration Limits: Prior to beginning vibration analysis of coal mining equipment , a review was made of The crushers handle lump coal and oversize rock, crushing 4.

    Our diagnostic experts have. Get Price arto ahlsten condition monitoring appliions of crushing plant Oct 5, bearing of the crusher and monitoring vibration of machine's main conveyor.

    The used.. Accordingly they implemented changes in design of fixtures, mass and mounts as well. They found that the Parameters focused in the experimentation are as follows: The load is increased in the steps zero, five, analyzer setup.

    In the experimentation while taking readings ten percent and so on up to thirty percent. Due to engine an acceleration transducer having piezoelectric sensor is operating constraints the load is not increased above thirty used, this is placed at three different locations to get percents.

    Schematic Line Diagram of Experimental Setup Equipments used in the experimentation are enlisted below: Accelerometer with Piezoelectric Sensor 1. Single Cylinder Diesel Engine 2. OR3X Analyzer 4. Digital Tachometer 3. Piezoelectric Accelerometer amplitudes divided by no. Tachometer Table 1. Observation table Engine Specifications Details are as follows: In 0C. Speed RPM. Fuel Rate 1. FFT Analyzer Specifications: Figure 2. Time vs Acceleration measurement 1 in Y Longitudinal vibrations in X direction: Frequency vs Acceleration Measurement 1 in Y direction Figure 7.

    Frequency vs Acceleration Measurement 1 in X direction Figure 4. Time vs Acceleration Measurement 2 in Y direction Figure 8. Time vs Acceleration Measurement 2 in X direction Figure 5. Frequency vs Acceleration Measurement 2 in Y direction By taking the signatures of acceleration, vibration behavior in Y direction is observed.

    Observations for vibrations in Y direction are: Figure 9. Observations for vibrations in X direction are: Frequency vs Acceleration Measurement 2 in Z amplitudes. By taking the signatures of acceleration, vibration behavior in Z direction is observed.

    Fuel Rate is increasing. Longitudinal vibrations in Z direction: Figure By making use of engine multibody rigid modeling a mathematical model generation becomes achievable as well as simplified. There may be number of such models can be developed by making use of different initial conditions while considering engine as a rigid body. Now the observations of conducted experimentation are: In above the vibrations are greater in Y direction as compared with X Figure Frequency vs Acceleration Measurement 1 in Z and Z direction.

    As the speed of engine decreases the vibration acceleration amplitude also decreases in Y direction but increases in X and Z direction. As load on engine increases vibration acceleration amplitude also decreases in Y direction but increases in X and Z direction. Hoffman, D. Winton, David R. Ramachandran, K. Padmanaban and J. Snyman, P. Heyns, P. Theory 30 1: Charles, Jyothi Sinha, F.

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