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ISO 7919-3-2009 pdf free download

It Is necessary to appreciate that a criterion based on change of vibration has limited application, since significant changes of varying magnitude and rates can and do occur in individual frequency components, but the importance of these is not necessarily reflected in the broad-band vibration signal (see ISO 7919-1). For example, the propagation of a crack in a rotor can introduce a progressive change in vibration components at multiples of rotational frequency, but their magnitude might be small relative to the amplitude of the once-per- revolution rotational frequency component, Consequently, it can be difficult to identify the effects of the crack propagation by looking at the change in the broad-band vibration only. Therefore, although monitoring the change in broad-band vibration will give some indication of potential problems. it might be necessary in certain applications to use measuring and analysis equipment which is capable of determining the trends of the vector changes that occur in individual frequency components of the vibration signal. This equipment can be more sophisticated than that used for normal supervisory monitoring and its use and application requires specialist knowledge. Hence, the specification of detailed criteria for measurements of this type is beyond the scope of this part of ISO 7919.
A.4 Operational limits
For many machines. mainly those of small size or power, continuous monitoring of vibration is not necessary. However, for those machines for which continuous monitoring of vibration is employed, it is common practice to establish operational vibration limits. These limits take the form of ALARMS and TRIPS.
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 necessary. In general, if an ALARM situation occurs, operation 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 limit 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 specified for different measurement positions and directions.
A.4.1 Setting of ALARMS
The ALARM limits may vary considerably for individual machines. The values chosen will normally be set relative to a baseline value determined from experience for the measurement position or direction for that particular machine.
It is recommended that the ALARM limit be set higher than the baseline by an amount equal to 25 % of the zone boundary B/C. If the baseline is low, the ALARM may be below zone C.
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 machines or relative to agreed acceptance values. ISO 7919-3-2009 pdf free download.

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