Accelerometers: Design, Theory, and Application

An Instrumentation Report By

C.J. Hartwigsen

10/17/01

Vibration Measurement

Many Systems Require Vibration Analysis Vibration Systems (Car Suspension) Systems Subject to Periodic Loading or Shock

Experimental Vibration Analysis Requires Measurement of Motion Displacement Velocity Acceleration

Motion Transducers

Displacement LVDT Capacitive Transducer Laser Transducer

Velocity Inductive Transducer Laser Velocimeter

Acceleration The Accelerometer!

Advantages of Accelerometer (Piezoelectric)

Requires No Power Supply No Moving Parts Compact Robust Large Dynamic Range Large Frequency Range Easy to Use Cheap

Can Be Used in Any Orientation

Insensitive to Normal Environments

Long-Term Stability Displacement, Velocity

Obtainable Through Integration

Principle of Operation

Physical Setup: Piezoelectric Material Sandwiched Between Base and Resonant Mass - Also Shear, Bender

Motion Causes Resonant Mass to Move, Force to Move Mass Is Transmitted Through Piezoelectric Material (F = ma)

Compression/Tension or Shear of Piezoelectric Material Causes Charge Buildup Proportional to Acceleration

Equivalent Electric Circuit Measures Capacitance Depends On Cable

ICP Accelerometers

Integrated Circuit Piezoelectric To Make Accelerometer Use Simple, Incorporate Electronics

Package Into Transducer Equivalent Circuit => No Dependence on Cable Output Sensitivity Constant

Characteristics of Accelerometers

Dynamic Range: Should Be Able to Measure Low and High Level Vibration Lower Limit is Noise Upper Limit is Set By Accelerometer

Frequency Range: Should Be Able to Measure Across a Broad Bandwidth Accelerometer is SDOF system w/ Frequency Response

Physical Dimensions Weight Size

Use and Handling of Accelerometers

Selection Check Dynamic Range & Sensitivity Check Frequency Range Check Operational Environment Investigate Effect of Accelerometer on Structure => Mass

Mounting Direct Mounting w/Stud Cement Wax Magnetic Base

Use and Handling of Accelerometers

Do Not Let Cables Influence Structure (Particularly if Small and Light)

Do Not Drop Be Aware of Noise

AcousticCan Affect StructureCan Affect Transducer

Electric

If Digitizing Data, Watch Out For Aliasing Should Be Calibrated Periodically

Accelerometer Producers

PCB Piezotronics 3425 Walden Avenue Depew, NY 14043 716-684-0001 sales@pcb.com

Kistler Instrument Corp 75 John Glenn Drive Amherst, NY 14228 716-691-5100 sales.us@kistler.com

Endevco Corporation 30700 Rancho Viejo Road San Juan Capistrano, CA 92675 1-800-9826732 applications@endevco.com