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| home >> engineering information >> Vibration Systems Engineering Information | ||||||||||
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| General | ||||||||||
| Labworks manufactures a range of electrodynamic transducers (shakers) as well as a series of high dissipation shaker power amplifiers and vibration controllers. These shakers and amplifiers, in various combinations, yield a wide variety of vibration performance levels. Labworks has selected several combinations (or systems) that yield cost effective solutions to the most common requirements. These systems include all necessary shaker to amplifier interconnecting cables as well as a cooling vacuum and hose when cooling is required. Systems with PA-123 series amplifiers are supplied with an amplifier rack panel cabinet. | ||||||||||
| When shakers are matched with different amplifiers, systems with specific vibration capabilities are produced. The current system specifications, rather than the individual component specifications reflect these capabilities. Of course, the system specifications will be equal to or less than the individual shaker maximum ratings. | ||||||||||
| In addition to the basic Labworks system consisting of a shaker and an amplifier, we also offer vibration controllers and other accessories to tailor the system to specific needs. | ||||||||||
| Labworks shakers, amplifiers and controllers can be purchased separately, if desired, to upgrade existing test setups. See the individual data sheets on this site for specific data relative to these components. Feel free to call one of our vibration engineers if you have any questions regarding our components. | ||||||||||
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| Sine Vibration | ||||||||||
| Shaker systems are usually rated by their sinusoidal vibration peak force capabilities. Since electrodynamic shakers are primarily force generators, a shaker system must provide the force necessary to produce the accelerations required on the test specimen and its mounting fixture. This required force is readily calculated by multiplying the sinusoidal peak acceleration desired by the total moving mass. The total moving mass includes the test specimen, its mounting fixture and the shakers armature. The system selector graphs and procedure on this site include the shaker’s armature, therefore, only the test specimen and its fixture weight is used on the payload axis of these graphs. If an exact calculation is desired, Labworks armature weights can be found on the shaker individual data pages as well as on the system selector pages. A short cut to this calculation is generally practiced in the industry by specifying the acceleration in g’s pk (acceleration of gravity) and then using the total moving weight in place of mass in the normal F = ma equation and the related equations of motion for velocity and displacement. | ||||||||||
| For example: Test specimen weight: 3 pounds Test fixture weight: 0.5 pounds Test specification: sine sweep, 20 to 200 Hz, 10 g pk |
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| From the Sine Vibration Capabilities graph, the intersection of 3.5 pounds and 10 g pk falls just above the LW-139-40 and below the LW-139-75 curves. From the System Specifications table, both of these systems utilize the ET-139 shaker which has a 1.0 pound armature. To check the requirement: | ||||||||||
| 10 gpk x (3.0 lb + 0.5 lb +1.0 lb) = 45 lb force pk | ||||||||||
| The LW-139-75 system should be selected because the force required is above the capability of the LW-139-40 system. To check the required displacement for the specification, use the formula for sine displacement from the engineering section of this site and calculate it for the lowest specification frequency (which is the highest displacement for constant acceleration). | ||||||||||
| From above: 10g pk @ 20 Hz | ||||||||||
| Dreq = g / .0511 f 2
+ 2 w/k* = 10 / (.0511 x 202)+ (2 x 4.5 / 60) = 0.639 inch pk-pk *the 2w/k term for vertical operation only w = total load, k = shaker flexure stiffness |
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| Checking the System Components table shows the Displacement for the LW-139-75 system to be 1.0 inch pk-pk maximum and therefore it is a suitable system for this requirement. | ||||||||||
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| Random Vibration | ||||||||||
| Random vibration calculations proceed exactly the same as sine except that the Random Vibration Capabilities graph and System Specifications random force must be substituted. Acceleration in g’s RMS and displacement in inches pk-pk must be known or calculated using the engineering equations found in the engineering section of this site. | ||||||||||
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