| It has been shown many times over that the
| |
| | machinery diagnostics.
|
| vibration signature of an operating
| |
| | In general, it is desirable to locate the
|
| machine provides far more information
| |
| | test transducer as close as possible to
|
| about the inner workings of the machine
| |
| | the bearing with solid metal between the
|
| than any other type of non-destructive
| |
| | bearing and the sensor. Avoid bearing
|
| test. A bearing that has a small
| |
| | caps, which are of thin metal and are thus
|
| developing defect will cause a telltale
| |
| | poor conductors of vibration energy.
|
| change in the machine vibration, as will
| |
| | If possible, pick test point locations so
|
| an imbalance condition, a misalignment, or
| |
| | that there is no metal-to-metal joint
|
| any of a myriad of other faults.
| |
| | between the bearing and the sensor. The
|
| Vibration analysis, properly applied,
| |
| | joint between the end bell and stator
|
| allows the technician to detect small
| |
| | housing of a motor is an example of this.
|
| developing mechanical defects long before
| |
| | Fan housings on the ends of motors are
|
| they become a threat to the integrity of
| |
| | also to be avoided.
|
| the machine, and thus provides the
| |
| | In general, it has been found that for
|
| necessary lead-time to schedule
| |
| | motors of less than about 50 HP, one test
|
| maintenance to suit the needs of the plant
| |
| | point is adequate, but for motors over 50
|
| management. In this way, plant management
| |
| | HP, each bearing should have its own test
|
| has control over the machines, rather than
| |
| | point. In any machines that are especially
|
| the other way around.
| |
| | sensitive to bearing damage, and bearing
|
| Vibration measurement and analysis is the
| |
| | problems should be detected as early as
|
| cornerstone of Predictive Maintenance,
| |
| | possible, each bearing should have its own
|
| which stands in sharp contrast to the
| |
| | test point.
|
| historical "run-to-failure" type of
| |
| | Another consideration in the integrity of
|
| maintenance practice. Numerous studies,
| |
| | the path between the bearing itself and
|
| such as those conducted by the Electric
| |
| | the transducer: If the motor and bell is a
|
| Power Research Institute (EPRI), have
| |
| | solid casting, it will effectively
|
| shown that on average, the cost to
| |
| | transmit vibration with little loss of
|
| industry for maintenance will be reduced
| |
| | high frequencies, but if it contains one
|
| by more than 50% if a predictive
| |
| | or more metal to metal connections, the
|
| maintenance program is used instead of
| |
| | high frequencies will be significantly
|
| run-to-failure.
| |
| | distorted.
|
| The first vibration meters were introduced
| |
| | In any machinery-monitoring program, it is
|
| in the 1950s, and they measured the
| |
| | extremely important that the data is
|
| overall, or "broad band" level of machine
| |
| | collected in exactly the same manner each
|
| vibration, either in peak-to-peak mils
| |
| | time a measurement is taken. This is to
|
| (thousandths of an inch) of vibratory
| |
| | assure that the data is repeatable and can
|
| displacement, or in inches per second
| |
| | be trended over time. For this reason, it
|
| (IPS) of vibration velocity. A little
| |
| | is not recommended that hand-held
|
| later, tunable analog filters were added
| |
| | transducers be used. By far the most
|
| to the meters in order to discriminate
| |
| | reliable data is collected when the
|
| between different frequency components,
| |
| | transducer is stud mounted to the machine
|
| and thus to produce a sort of vibration
| |
| | surface.
|
| spectrum.
| |
| | To assist in the determination of machine
|
| The 1970s brought forth the personal
| |
| | problems, it is very helpful to have
|
| computer and the advent of digital signal
| |
| | vibration data from each measurement point
|
| processing that led to the FFT analyzer,
| |
| | in three directions. These directions are
|
| and it made quick work of calculating a
| |
| | called Axial, Radial, and Tangential.
|
| frequency spectrum from a recorded
| |
| | Axial is the direction parallel to the
|
| vibration signal. The first such analyzers
| |
| | shaft in question, radial is the direction
|
| were quite bulky, weighing as much as 75
| |
| | from the transducer to the center of the
|
| pounds, and this made them more suited as
| |
| | shaft, and tangential is 90 degrees from
|
| laboratory instruments than portable units
| |
| | radial, tangent to the shaft.
|
| for field use.
| |
| | To assist in the determination of machine
|
| The 1980s saw the exploitation of the
| |
| | problems, it is very helpful to have
|
| microprocessor on a single silicon chip,
| |
| | vibration data from each measurement point
|
| and the battery-powered truly portable
| |
| | in three directions. These directions are
|
| digital signal analyzer quickly followed
| |
| | called Axial, Radial, and Tangential.
|
| this. It is this device, coupled with a
| |
| | Axial is the direction parallel to the
|
| computer program that stores the data and
| |
| | shaft in question, radial is the direction
|
| takes care of the logistics of vibration
| |
| | from the transducer to the center of the
|
| data collection that has revolutionized
| |
| | shaft, and tangential is 90 degrees from
|
| the application of vibration analysis to
| |
| | radial, tangent to the shaft.
|
