IMI Industrial Vibration Sensors Katalog Seite 170

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Stud Mounted Accelerometer Screw Mounted Accelerometer Shear Mode Shear mode accelerometer designs feature sensing crystals attached between a center post and a seismic mass A compression ring or stud applies a pre load force to the element assembly to insure a rigid structure and linear behavior Under acceleration the mass causes a shear stress to be applied to the sensing crystals This stress results in a proportional electrical output by the piezoelectric material The output is collected by electrodes and transmitted by lightweight lead wires to either the built in signal conditioning circuitry of ICP sensors or directly to the electrical connector for charge mode types By having the sensing crystals isolated from the base and housing shear mode accelerometers excel in rejecting thermal transient and base bending effects Also the shear geometry lends itself to small size which promotes high frequency response while minimizing mass loading effects on the test structure With this combination of ideal characteristics shear mode accelerometers offer optimum performance Sensor Mounting and Frequency Response One of the most important considerations in dealing with accelerometer mounting is the effect the mounting technique has on the accuracy of the usable frequency response The accelerometer s operating frequency range is determined in most cases by securely stud mounting the test sensor directly to the reference standard accelerometer The direct stud mounted coupling to a very smooth surface generally yields the highest mounted resonant frequency and therefore the broadest usable frequency range The addition of any mass to the accelerometer such as an adhesive or magnetic mounting base lowers the resonant frequency of the sensing system and may affect the accuracy and limits of the accelerometer s usable frequency range Also compliant materials such as a rubber interface pad can create a mechanical filtering effect by isolating and damping high frequency transmissibility Surface Preparation For best measurement results especially at high frequencies it is important to prepare a smooth and flat machined surface where the accelerometer is to be attached Inspect the area to ensure that no metal burrs or other foreign particles interfere with the contacting surfaces The application of a thin layer of silicone grease between the accelerometer base and the mounting surface also assists in achieving a high degree of intimate surface contact required for best high frequency transmissibility Stud Mounting For permanent installations where a very secure attachment of the accelerometer to the test structure is preferred stud mounting is recommended First grind or machine on the test object a smooth flat area at least the size of the sensor base per the manufacturer s specifications Then prepare a tapped hole in accordance with the supplied installation drawing ensuring that the hole is perpendicular to the mounting surface Install accelerometers with the mounting stud and make certain that the stud does not bottom in either the mounting surface or accelerometer base Most IMI mounting studs have depth limiting shoulders that ensure that the stud cannot bottom out into the accelerometer s base Each base incorporates a counterbore so that the accelerometer does not rest on the shoulder Acceleration is transmitted from the structure s surface into the accelerometer s base Any stud bottoming or interfering between the accelerometer base and the structure inhibits acceleration transmission and affects measurement accuracy When tightening apply only the recommended torque to the accelerometer A thread locking compound may be applied to the threads of the mounting stud to safeguard against loosening Shear Mode Accelerometer ICP Sensor Circuit Cover Piezoelectric Material Seismic Mass Preload Ring Base with Threaded Mounting Hole Lead Wire Electrical Connector Accelerometer Maintain Clearance Maintain Clearance Silicone Grease Silicone Grease Technical Information visit us online at www imi sensors com 1 716 684 0003 167


Vorschau IMI Industrial Vibration Sensors Katalog Seite 170