Accelerometers: Design, Theory, and Application An Instrumentation Report By C.J. Hartwigsen 10/17/01

Vibration Measurement FMany Systems Require Vibration Analysis GVibration Systems (Car Suspension) GSystems Subject to Periodic Loading or Shock FExperimental Vibration Analysis Requires Measurement of Motion GDisplacement GVelocity GAcceleration

Motion Transducers FDisplacement GLVDT GCapacitive Transducer GLaser Transducer FVelocity GInductive Transducer GLaser Velocimeter FAcceleration GThe Accelerometer!

Advantages of Accelerometer (Piezoelectric) FRequires No Power Supply FNo Moving Parts FCompact FRobust FLarge Dynamic Range FLarge Frequency Range FEasy to Use FCheap FCan Be Used in Any Orientation FInsensitive to Normal Environments FLong-Term Stability FDisplacement, Velocity Obtainable Through Integration

Principle of Operation FPhysical Setup: Piezoelectric Material Sandwiched Between Base and Resonant Mass - Also Shear, Bender FMotion Causes Resonant Mass to Move, Force to Move Mass Is Transmitted Through Piezoelectric Material (F = ma) FCompression/Tension or Shear of Piezoelectric Material Causes Charge Buildup Proportional to Acceleration FEquivalent Electric Circuit GMeasures Capacitance GDepends On Cable

ICP Accelerometers FIntegrated Circuit Piezoelectric FTo Make Accelerometer Use Simple, Incorporate Electronics Package Into Transducer FEquivalent Circuit => No Dependence on Cable FOutput Sensitivity Constant

Characteristics of Accelerometers FDynamic Range: Should Be Able to Measure Low and High Level Vibration GLower Limit is Noise GUpper Limit is Set By Accelerometer FFrequency Range: Should Be Able to Measure Across a Broad Bandwidth GAccelerometer is SDOF system w/ Frequency Response FPhysical Dimensions GWeight GSize

Use and Handling of Accelerometers FSelection GCheck Dynamic Range & Sensitivity GCheck Frequency Range GCheck Operational Environment GInvestigate Effect of Accelerometer on Structure => Mass FMounting GDirect Mounting w/Stud GCement GWax GMagnetic Base

Use and Handling of Accelerometers FDo Not Let Cables Influence Structure (Particularly if Small and Light) FDo Not Drop FBe Aware of Noise GAcoustic GCan Affect Structure GCan Affect Transducer GElectric FIf Digitizing Data, Watch Out For Aliasing FShould Be Calibrated Periodically

Accelerometer Producers FPCB Piezotronics 3425 Walden Avenue Depew, NY FKistler Instrument Corp 75 John Glenn Drive Amherst, NY FEndevco Corporation Rancho Viejo Road San Juan Capistrano, CA