What is a Piezoelectric Accelerometer? Vibration Sensor • Portable balancer, vibration analyzer "Balanset" for dynamic balancing crushers, fans, mulchers, augers on combines, shafts, centrifuges, turbines, and many others rotors What is a Piezoelectric Accelerometer? Vibration Sensor • Portable balancer, vibration analyzer "Balanset" for dynamic balancing crushers, fans, mulchers, augers on combines, shafts, centrifuges, turbines, and many others rotors

What is a Piezoelectric Accelerometer? Vibration Sensor

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Understanding Piezoelectric Accelerometers

Definition: What is a Piezoelectric Accelerometer?

Piezoelectric accelerometer is a vibration sensor that uses the piezoelectric effect—where certain crystals generate electrical charge when mechanically stressed—to convert mechanical acceleration into an electrical signal proportional to vibration amplitude. When the sensor experiences acceleration, an internal mass (seismic mass) compresses or stretches piezoelectric crystal elements, generating an electrical charge or voltage that is conditioned and output as a measurement signal.

Piezoelectric accelerometers are the most widely used vibration sensors in industrial applications due to their wide frequency range (0.5 Hz to 50+ kHz), high sensitivity, robustness, and self-generating nature (requiring no external power source for the sensing element itself). They form the foundation of modern vibration analysis and condition monitoring programs.

Piezoelectric Effect

Physical Principle

  • Certain crystals (quartz, tourmaline) and ceramics (PZT, barium titanate) are piezoelectric
  • Mechanical stress generates electric charge on crystal surfaces
  • Charge proportional to applied force
  • Reversible effect (applying voltage causes deformation)
  • Self-generating (no power needed for charge generation)

In Accelerometer

  1. Vibration accelerates sensor base and housing
  2. Internal seismic mass experiences force (F = m × a)
  3. Force compresses piezoelectric crystal
  4. Crystal generates charge proportional to force (and thus acceleration)
  5. Charge collected on electrodes and converted to measurable signal

Types of Piezoelectric Accelerometers

By Internal Design

Compression Type

  • Most common design
  • Crystal compressed between mass and base
  • Rugged, wide temperature range
  • Good for harsh environments

Shear Type

  • Crystal sheared by mass motion
  • Excellent base strain isolation
  • Better low-frequency response
  • Less sensitive to temperature transients
  • Premium performance

Flexural (Bending) Type

  • Crystal in bending configuration
  • High sensitivity possible
  • Less common in industrial applications

By Electronics Type

Charge Mode

  • Output is charge (picocoulombs)
  • Requires external charge amplifier
  • Extreme temperature capability (to 650°C)
  • High-impedance output (sensitive to cable)
  • Specialized applications

IEPE/ICP (Voltage Mode)

  • Built-in electronics convert charge to voltage
  • IEPE is industry standard
  • Low-impedance output
  • Simple connectivity
  • 95%+ of industrial applications

Performance Specifications

Sensitivity

  • Output per unit acceleration (mV/g, pC/g)
  • Typical: 10-100 mV/g for IEPE; 1-100 pC/g for charge mode
  • Higher sensitivity = better resolution but lower range
  • Selection based on expected vibration levels

Frequency Range

  • Low Frequency: 0.5-5 Hz depending on electronics
  • High Frequency: 5-50 kHz to resonance
  • Usable Range: Typically to 1/3 of resonance frequency
  • Mounting Affects: Mounting method limits high-frequency response

Amplitude Range

  • General purpose: ±50g to ±500g
  • High sensitivity: ±5g to ±50g
  • Shock sensors: ±500g to ±10,000g
  • Must not exceed range (clipping, damage)

Selection Criteria

For General Machinery Monitoring

  • 100 mV/g IEPE accelerometer
  • ±50g range
  • Frequency range 1 Hz – 10 kHz
  • Industrial temperature rating (-40 to +120°C)
  • Hermetically sealed

For Bearing Defect Detection

  • Higher frequency response (to 20+ kHz)
  • Moderate sensitivity (10-50 mV/g)
  • Wide dynamic range
  • Stud mounting for best high-frequency coupling

For High-Temperature Applications

  • High-temp IEPE (to 175°C) or charge mode (to 650°C)
  • Special mounting and cabling
  • May sacrifice some performance for temperature capability

Mounting and Installation

Mounting Effects on Performance

  • Stud Mount: Best (flat to 10+ kHz)
  • Adhesive: Good (flat to 7-8 kHz)
  • Magnetic: Acceptable (flat to 2-3 kHz)
  • Probe/Handheld: Poor (limited to low frequencies, qualitative)

Installation Requirements

  • Clean, flat mounting surface
  • Proper torque for stud mounting
  • Thin, even adhesive layer
  • Magnetic base fully seated
  • Cable secured to prevent pulling

Piezoelectric accelerometers, particularly IEPE types, are the backbone of industrial vibration monitoring. Their combination of wide frequency response, high sensitivity, robustness, and (for IEPE) simplicity makes them the sensor of choice for condition monitoring, diagnostics, and balancing in the vast majority of rotating machinery applications worldwide.

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