Understanding Shear Accelerometers

Devices

Portable balancer & Vibration analyzer Balanset-1A

$2,353.83

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Vibration sensor

$107.26

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Optical Sensor (Laser Tachometer)

$147.78

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Balanset-4

$8,107.90

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Magnetic Stand Insize-60-kgf

$54.82

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Reflective tape

$11.92

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Dynamic balancer “Balanset-1A” OEM

$2,067.80

Definition: What is a Shear Accelerometer?

Shear accelerometer (also called shear-mode accelerometer) is a type of piezoelectric accelerometer where the internal seismic mass applies shear stress (rather than compressive stress) to the piezoelectric crystal elements when acceleration occurs. This shear-mode configuration provides superior base strain isolation (immunity to mounting surface distortion), better thermal transient response, and lower sensitivity to mounting torque variations compared to compression-mode designs, making shear accelerometers the premium choice for critical vibration measurements requiring highest accuracy and stability.

While more expensive than standard compression-mode accelerometers, shear-mode sensors are widely used in precision applications, reference standards, permanent monitoring systems, and any situation where measurement quality justifies the additional cost.

Construction and Operating Principle

Internal Design

• Center Post: Rigid mounting stud through sensor center
• Seismic Mass: Ring or cylinder around center post
• Piezo Elements: Crystals bonded between mass and center post
• Preload: Mass preloaded against crystals
• Shear Configuration: Acceleration causes tangential (shear) stress on crystals

How Shear Mode Works

1. Housing accelerates with vibration
2. Seismic mass resists acceleration (F = m × a)
3. Mass tries to slide tangentially relative to center post
4. Creates shear stress in piezoelectric elements
5. Shear stress generates electrical charge
6. Charge proportional to acceleration

Advantages Over Compression Mode

Base Strain Isolation

The primary advantage:

• Mounting surface bending doesn’t affect crystal stress directly
• Shear elements isolated from base strain
• Can mount on thin, flexible structures without errors
• Compression mode shows false signals from base strain
• Critical for measurements on sheet metal, lightweight housings

Thermal Transient Immunity

• Better rejection of temperature changes
• Lower pyroelectric effect (charge from temperature change)
• More stable zero point
• Important for measurements with temperature variations

Mounting Torque Insensitivity

• Performance less affected by stud torque variations
• More repeatable installation
• Less critical torque control needed

Better Stability

• Lower drift over time
• More stable calibration
• Preferred for reference and metrology

Applications

Reference Standards

• Calibration reference sensors
• Metrology and standards laboratories
• Back-to-back calibration masters
• Highest accuracy required

Critical Machinery Monitoring

• High-value equipment permanent monitoring
• Nuclear power plants
• Large turbomachinery
• Where reliability and accuracy paramount

Precision Measurements

• Modal testing and structural dynamics
• Research and development
• Acceptance testing
• Contractual verification measurements

Difficult Mounting Situations

• Thin sheet metal structures
• Lightweight machine housings
• Flexible mounting surfaces
• Where base strain would affect compression sensors

Performance Characteristics

Frequency Range

• Similar to compression accelerometers
• Low frequency: 0.5-5 Hz depending on design
• High frequency: to resonance (20-70 kHz depending on size)
• Usable range very wide

Amplitude Range

• Typically ±50g to ±500g
• Similar to compression designs
• Specialized versions for higher or lower ranges

Temperature Performance

• Standard: -50 to +120°C
• High-temp versions: to 175°C
• Better thermal stability than compression
• Lower zero shift with temperature

Cost Considerations

Higher Cost

• Typically 2-4× cost of compression accelerometers
• More complex manufacturing
• Tighter tolerances required
• Premium materials and processes

Cost Justification

• Critical applications where accuracy essential
• Difficult mounting situations
• Reference standards and calibration
• Long-term permanent installations
• When measurement errors costly

Selection Criteria

Choose Shear Mode When:

• Mounting on thin or flexible structures
• Temperature transients expected
• Highest accuracy required
• Reference or calibration application
• Long-term permanent installation with stability critical

Compression Mode Adequate When:

• Routine industrial monitoring
• Rigid mounting surfaces
• Budget constraints
• Standard accuracy sufficient
• Temporary measurements

Manufacturers and Models

• Most accelerometer manufacturers offer shear designs
• Often designated as “premium” or “precision” models
• Industrial accelerometers: many are shear mode
• IEPE and charge-mode versions both available

Shear accelerometers represent the premium tier of piezoelectric vibration sensors, offering superior base strain rejection, thermal stability, and measurement accuracy compared to compression designs. While their higher cost limits use to critical applications, shear-mode sensors are the optimal choice when measurement quality is paramount, mounting conditions challenging, or long-term stability essential.

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