Understanding Sensor Sensitivity

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Portable balancer & Vibration analyzer Balanset-1A

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Dynamic balancer “Balanset-1A” OEM

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Definition: What is Sensitivity?

Sensitivity is the ratio of a sensor’s output signal to the input physical quantity being measured, representing the sensor’s gain or conversion factor. For vibration sensors, sensitivity defines how much electrical output (voltage or charge) is produced per unit of vibration (acceleration, velocity, or displacement). Higher sensitivity means larger output signal for given vibration level, providing better resolution and signal-to-noise ratio but limiting maximum measurement range before sensor output saturates.

Sensitivity is the fundamental specification that must be known to convert sensor output voltage into meaningful vibration units. It is determined during manufacturing calibration, documented on calibration certificates, and used in all vibration calculations. Understanding sensitivity trade-offs enables proper sensor selection for specific measurement requirements.

Sensitivity Units by Sensor Type

Accelerometers

IEPE/Voltage Mode

• Units: mV/g (millivolts per g of acceleration)
• Typical Values: 10-1000 mV/g
• Standard: 100 mV/g most common
• High Sensitivity: 500-1000 mV/g (low vibration applications)
• Low Sensitivity: 10-50 mV/g (high vibration, shock applications)

Charge Mode

• Units: pC/g (picocoulombs per g)
• Typical Values: 1-1000 pC/g
• General Purpose: 10-50 pC/g common

Velocity Sensors

• Units: mV per in/s or mV per mm/s
• Typical: 100 mV/in/s or ~4000 mV/mm/s
• Alternative Units: V per m/s

Displacement Probes

• Units: mV/mil or V/mm
• Typical: 200 mV/mil or 7.87 V/mm (eddy current probes)
• Calibrated: For specific target material and gap range

Sensitivity Trade-offs

High Sensitivity (100-1000 mV/g)

Advantages

• Large output signal for low vibration
• Better resolution (can detect small changes)
• Better signal-to-noise ratio
• Good for low-vibration machinery

Disadvantages

• Limited dynamic range (saturates at lower vibration)
• Typical range: ±5g to ±50g
• Not suitable for high-vibration or shock applications

Low Sensitivity (10-50 mV/g)

Advantages

• Wide dynamic range
• Can measure high vibration (±100g to ±10,000g)
• Suitable for shock and impact
• Won’t saturate in high-vibration conditions

Disadvantages

• Smaller output for low vibration
• Lower signal-to-noise ratio
• Reduced resolution
• May miss small vibration changes

Sensitivity Selection

Based on Application

Low Vibration (< 5 mm/s)

• Use high sensitivity (100-500 mV/g)
• Precision machinery, low-speed equipment
• Need good resolution for small changes

Moderate Vibration (5-20 mm/s)

• Standard sensitivity (50-100 mV/g)
• General industrial machinery
• Most common application range

High Vibration (> 20 mm/s)

• Low sensitivity (10-50 mV/g)
• Prevent saturation
• Crushers, mills, high-unbalance equipment

Shock and Impact

• Very low sensitivity (1-10 mV/g)
• Measure to ±1000g or more
• Impact testing, crash testing

Effect on Measurements

Signal Level

• Higher sensitivity → larger signal voltage
• Better utilizes instrument input range
• Improved resolution
• But limits maximum measurable vibration

Dynamic Range

• Range from noise floor to saturation
• High sensitivity: narrow range (good for small signals)
• Low sensitivity: wide range (good for variable signals)
• Trade-off between resolution and range

Noise Performance

• Sensor inherent noise (electrical noise in electronics)
• Higher sensitivity = better signal-to-noise for low vibration
• Noise becomes more significant with lower sensitivity

Calibration and Verification

Factory Calibration

• New sensors calibrated at factory
• Sensitivity marked on sensor or certificate
• Tolerance typically ±5-10%
• Should verify before critical use

Periodic Recalibration

• Sensitivity can drift over time
• Recalibrate annually or per schedule
• Updated sensitivity from calibration certificate
• Enter in instrument or apply corrections

Field Verification

• Handheld calibrator provides known vibration
• Verify sensor output matches expected (sensitivity × input)
• Quick check before critical measurements

Related Specifications

Measurement Range

• Maximum vibration sensor can measure
• Inversely related to sensitivity
• Example: 100 mV/g with ±5V output → ±50g range

Resolution

• Smallest vibration change detectable
• Limited by noise and digitization
• Higher sensitivity generally better resolution

Linearity

• How constant sensitivity remains over measurement range
• Good sensors: < 1% deviation from linear
• Specified as % full-scale error

Practical Considerations

Instrument Input Matching

• Instrument input range must match sensor output
• Example: 100 mV/g sensor × 50g vibration = 5V output (must fit in instrument ±5V input)
• Adjustable input gains accommodate different sensitivities

Multiple Sensors

• Using sensors with different sensitivities in one program
• Must configure instrument for each sensor
• Error if wrong sensitivity entered
• Standardizing on one sensitivity simplifies operations

Sensor sensitivity is a fundamental specification that defines the conversion between physical vibration and electrical signal. Understanding sensitivity units, selection criteria based on expected vibration levels, and proper sensitivity entry in measurement instruments is essential for accurate vibration measurements, appropriate sensor selection, and avoiding measurement errors from sensitivity mismatches or saturation.

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