The requirement for operational monitoring is usually met by performing one or both measurements in the radial direction i. These can be supplemented by a measurement of axial vibration. The latter is normally of prime significance at thrust bearing locations where direct axial dynamic forces are transmitted.
Detailed recommendations for specific machine types are provided in the additional parts of IS0 In this case it is important to ensure that all the major components of the machine and structure are installed when testing is carried out.
It should be noted that valid comparisons of vibration for machines of the same type but on different foun- dations or sub-foundations can only be made if the foundations concerned have similar dynamic charac- teristics. IS0 E 6 Figure 3 - Measuring points for small electrical machines Figure 4 - Measuring points for reciprocating engines 7.
IS0 E 0 IS0 3. The support structure can significantly affect the measured vibration and every attempt should be made to ensure that the natural frequencies of the complete test arrangement do not coincide with the rotational frequencies of the machine or with any of its significant harmonics. Additionally, the test arrangement shall not cause a substantial change in any of the major resonance frequencies. If a significant support resonance is present during acceptance testing and it cannot be eliminated, the vibration acceptance tests may have to be carried out on the fully installed machine in situ.
For some classes of machines e. In this case, all the rigid body mode frequencies of the ma- chine on its support system shall be less than one-half of the lowest significant excitation frequency of the machine.
Appropriate support conditions can be achieved by mounting the machine on a resilient support baseplate or by free suspension on a soft spring. Where possible, steps should be taken to reduce the magnitude of environmental vibration if it is greater than one-third of the recommended limits. Particular attention shall be given to ensuring that the vibration transducer is correctly mounted and that its presence does not affect the vibration response characteristics of the machine.
Two mon instrument systems itor broad-band vibrat presently in ion are acce common use to ptable, namely: a instruments which incorporate r. The scaling is based on an assumed sinusoidal relationship between r. If the vibration evaluation is based on more than one measurement quantity i. It is desirable that the measurement system should have provision for on-line calibration of the readout instrumentation and, in addition, have suitable isolated outputs to permit further analysis as required.
Additional vi- bration measurements that may be taken under other conditions are not applicable for evaluation in accord- ance with clause 5.
The evaluation criteria relate to both operational monitoring and ac- ceptance testing, and they apply only to the vibration produced by the machine itself and not to vibration transmitted from outside. For certain classes of ma- chinery, the guidelines presented in this part of IS0 are complemented by those given for shaft vibration in IS0 If the procedures of both standards are applicable, the one which is more restrictive shall generally apply.
One criterion considers the magnitude of observed broad-band. However, these values provide guidelines for ensuring that gross de- ficiencies or unrealistic requirements are avoided.
In certain cases, there may be specific features associ- ated with a particular machine which would require different zone boundary values higher or lower to be used.
In such cases, it is normally necessary to ex- plain the reasons for this and, in particular, to confirm that the machine will not be endangered by operating with higher vibration values. The maximum vibration magnitude ob- served at each bearing or pedestal is assessed against four evaluation zones established from international experience.
This maximum magnitude of vibration measured is defined as the vibration severity see 3. Different categorization and number of zones may apply for specific machine types, which are cov- ered by the additional parts of IS0 Interim values for the zone boundaries are presented in annex B. Zone A: The vibration of newly commissioned ma- chines would normally fall within this zone.
Zone B: Machines with vibration within this zone are normally considered acceptable for unrestricted long- term operation. Zone C: Machines with vibration within this zone are normally considered unsatisfactory for long-term con- tinuous operation.
Generally, the machine may be operated for a limited period in this condition until a suitable opportunity arises for remedial action. Zone D: Vibration values within this zone are normally considered to be of sufficient severity to cause dam- age to the machine. The vibration of a particular machine depends on its size, the characteristics of the vibrating body and mounting system, and the purpose for which it is de- signed.
It is therefore necessary to take account of the various purposes and circumstances concerned when specifying ranges of vibration measurement for different machine types.
For nearly all machines, re- gardless of the type of bearings used, measurements of the broad-band r. In most cases, it has been found that vibration vel- ocity is sufficient to characterize the severity of vi- bration over a wide range of machine operating speeds. However, it is recognised that the use of a single value of velocity, regardless of frequency, can lead to unacceptably large vibration displacements.
This is particularly so for machines with low operating speeds when the once-per-revolution vibration com- ponent is dominant. Similarly, constant velocity cri- teria for machines with high operating speeds, or with vibration at high frequencies generated by machine component parts can lead to unacceptable acceler- ations. Consequently, acceptance criteria based on velocity will take the general form of figure6. This in- dicates the upper and lower frequency limits fu and 3 and shows that below a defined frequency fX and above a defined frequency fy the allowable vibration velocity is a function of the vibration frequency see also annex C.
The r. IS0 E 0 IS0 For many machines, the broad-band vibration consists primarily of a single frequency component, often shaft rotational frequency.
In this case, the allowable vi- bration is obtained from figure6 as the vibration vel- ocity corresponding to that frequency. Examples are the following. The allowable vibration displacement and acceleration should be consistent with the velocity corresponding to the sloped portions of figure6. The equivalent broad-band velocity can be obtained using equation A. It should be noted that, except for the case when the broad-band vibration consists primarily of a single frequency component, a di- rect comparision of the frequency spectrum com- ponents with the curves of figure6 would yield misleading results.
This value should then be evaluated relative to the constant velocity between fX and fv- The evaluation criteria for specific machine types will be given in the additional parts of IS0 as they become available. Annex C provides additional guid- ance. For certain machine types, it may be necessary to define further criteria beyond those described by figure6 see for example, 5.
Zone0 Frequency, f Figure 6 - General form of vibration velocity acceptance criteria 8 A significant increase or decrease in broad-band vibration magnitude may occur which re- quires some action even though zone C of Criterion I has not been reached.
Such changes can be instan- taneous or progressive with time and may indicate that damage has occurred or be a warning of an im- pending failure or some other irregularity.
Criterion II is specified on the basis of the change in broad-band vibration magnitude occurring under steady-state op- erating conditions. When Criterion II is applied, the vibration measure- ments being compared shall be taken at the same transducer location and orientation, and under ap- proximately the same machine operating conditions.
Significant changes from the normal vibration magni- tudes should be investigated so that a dangerous situation may be avoided. Criteria for assessing changes of broad-band vibration for monitoring purposes are given in the additional parts of IS0 However, it should be noted that some changes may not be detected unless the dis- crete frequency components are monitored see 5. ALARMS: To provide a warning that a defined value of vibration has been reached or a significant change has occurred, at which remedial action may be nec- essary.
In general, if an ALARM situation occurs, op- eration can continue for a period whilst investigations are carried out to identify the reason for the change in vibration and define any remedial action. TRIPS: To specify the magnitude of vibration beyond which further operation of the machine may cause damage.
If the TRIP value is exceeded, immediate action should be taken to reduce the vibration or the machine should be shut down. Different operational limits, reflecting differences in dynamic loading and support stiffness, may be speci- fied for different measurement positions and di- rections. The values chosen will normally be set relative to a baseline value deter- mined from experience for the measurement position or direction for that particular machine.
It is recommended that the ALARM value should be set higher than the baseline by an amount equal to a proportion of the upper limit of zone B. Guidelines for specific machine types are given in the additional parts of IS0 Where there is no established baseline, for example with a new machine, the initial ALARM setting should be based either on experience with other similar ma- chines or relative to agreed acceptance values.
After a period of time, a steady-state baseline value will be established and the ALARM setting should be ad- justed accordingly. If the steady-state baseline changes for example after a machine overhaul , the ALARM setting should be revised accordingly.
Different operational ALARM settings may then exist for different bearings on the machine, reflecting differences in dynamic loading and bearing support stiffnesses. The values used will, therefore, generally be the same for all machines of similar design and would not normally be related to the steady-state baseline value used for setting ALARMS.
There may, however, be differences for machines of different design and it is not possible to give guide- lines for absolute TRIP values. This will in most cases be adequate for acceptance testing and oper- 9 However, in some cases the use of vector information for vibration assessment on certain machine types may be desirable. Vector change information is particularly useful in de- tecting and defining changes in the dynamic state of a machine.
In some cases, these changes would go undetected when using broad-band vibration meas- urements. This is demonstrated in annex D. The specification of criteria for vector changes is be- yond the present scope of this part of IS0 In most cases this is not significant.
In other cases the vibration sensitivity may be such that although the vibration magnitude for a particular machine is satisfactory when measured under certain steady-state conditions, it can become unsatisfactory if these conditions change. It is recommended that, in cases where some aspect of the vibration sensitivity of a machine is in question, agreement should be reached between the customer and supplier about the necessity and extent of any testing or theoretical assessment.
These are discussed further in annex E. The definition of evaluation criteria for such additional methods is beyond the scope of this part of IS0 IS0 E Annex A informative Vibratory waveform relationships It has been recognized for many years that using the measurement of r.
For simple alternating waveforms which are made up of a discrete number of harmonic com- ponents of known amplitude and phase, and do not contain significant random vibration or shock com- ponents, it is possible, by means of Fourier analysis, to relate various fundamental quantities e.
These have been derived elsewhere and it is not the purpose of this annex to cover this aspect of the subject. However, a number of useful relationships are summarized below. From measured vibration velocity versus time re- cords, the r. If the peak-to-peak displacement values of the vi- bration, sl, s2, In the case where the vibration consists of only two significant frequency components giving beats of r. A-3 The operation of interchanging vibration acceleration, velocity or displacement values can be accomplished only for single-frequency harmonic components using, for example, figure A.
II It is intended that evaluation criteria for specific machine types will be provided in additional parts of IS0 for different machine types. However, as a short-term expedient only, limited evaluation criteria are provided in table B. The values given are for the upper limits of zones A to C, respectively see 5. It is important, therefore, prior to using these values, to check that they have not been superseded by an additional part of IS0 This annex will be deleted when all of the relevant parts have been published.
The machine classifications are as follows. Class I: Individual parts of engines and machines, in- tegrally connected to the complete machine in its normal operating condition. Production electrical mo- tors of up to 15 kW are typical examples of machines in this category. Class III: Large prime-movers and other large ma- chines with rotating masses mounted on rigid and heavy foundations which are relatively stiff in the di- rection of vibration measurements.
Class IV: Large prime-movers and other large ma- chines with rotating masses mounted on foundations which are relatively soft in the direction of vibration measurements for example, turbogenerator sets and gas turbines with outputs greater than IO MW. For special groups of machines, single values of r. IS0 E Annex D informative Vector analysis of change in vibration Introduction Evaluation criteria are defined in terms of the normal steady-running value of broad-band vibration and any changes that may occur in the magnitude of these steady values.
The latter criterion has limitations be- cause some changes may only be identified by vector analysis of the individual frequency components. The development of this technique for other than synchronous vibration components is still in its infancy and criteria cannot be defined in this part of IS0 at present. Each of these components is defined by its frequency, ampli- tude and phase relative to some known datum.
Con- ventional vibration-monitoring equipment measures the magnitude of the overall complex signal and does not differentiate between the individual frequency components. However, modern diagnostic equipment is capable of analysing the complex signal so that the amplitude and phase of each frequency component can be identified.
This information is of great value to the vibration engineer, since it facilitates the diagnosis of likely reasons for abnormal vibration behaviour. Changes in individual frequency components, which may be significant, are not necessarily reflected to the same degree in the broad-band vibration and, hence, the criterion based on changes of broad-band vibration magnitude only may require supplementary phase measurements.
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