Types and Characteristics of Accelerometers

2024-11-03 2024-11-04

1. Piezoelectric Accelerometer

Operating Principle: Piezoelectric accelerometers generate an electric charge when an internal piezoelectric element deforms due to applied acceleration. The piezoelectric material produces a signal proportional to the stress, which corresponds to the acceleration. This charge is amplified and converted into an electrical signal to accurately detect vibrations and impacts. Due to its rapid dynamic response and accuracy in high-frequency vibrations, it is widely used in industrial applications, aerospace, and seismic observation.
Frequency Range: Capable of handling a broad range from 1 Hz to several tens of kHz, making it ideal for high-frequency vibration analysis in machinery and structures. It should be used cautiously near its resonance frequency. For example, PCB Piezotronics Model 352C33 offers frequency responses up to 30 kHz, enabling precise vibration measurement.
Price Range: From $150 to $3,500. Prices vary depending on the application, from industrial to high-precision aerospace models.
Sensitivity: Ranging from 10 mV/g to 1000 mV/g, allowing for high-sensitivity detection of subtle acceleration changes. High-sensitivity models are more susceptible to noise, so adjustments are needed for the measurement environment.
Temperature Range: Some models can withstand high temperatures, up to 250°C, though extreme temperature fluctuations may reduce sensitivity. Operation within specified temperature limits is recommended.
Non-Linearity: With non-linearity below 0.5%, these sensors provide stable measurements over a wide range. They are ideal for applications requiring precise capture of high-speed vibrations.
Example: The PCB Piezotronics Model 352C33 is commonly used for precise vibration and impact measurements in aerospace, automotive, and industrial machinery.
Advantages: Compact, robust design capable of accurately measuring high-speed vibrations and impacts, with models available for high-temperature environments.
Disadvantages: Not suitable for static acceleration (0 Hz, e.g., gravitational acceleration) measurement. Temperature dependency requires environmental adjustments.
Mounting Method: Secure attachment is essential, typically using screws, adhesives, or magnetic mounts. Flat, rigid mounting surfaces are recommended to prevent data inaccuracies.
Output Signal Type: Piezoelectric accelerometers typically output a high-impedance analog voltage signal corresponding to the generated charge. Many models have internal impedance conversion circuits, providing low-impedance signals that simplify signal processing, especially in IEPE (Integrated Electronics Piezoelectric) sensors.
Calibration: Calibration usually involves a known acceleration applied by an acceleration standard, verifying the sensor's frequency response and sensitivity. Dynamic calibration is commonly performed due to the difficulty of static calibration, using a 1 g reference for sensitivity adjustment.

2. Capacitive Accelerometer

Operating Principle: Capacitive accelerometers detect acceleration through changes in capacitance between internal electrodes. When acceleration is applied, the distance between electrodes shifts, causing a change in capacitance. This change is converted into a voltage, reflecting the acceleration level. Capacitive accelerometers can measure static acceleration (0 Hz) and are well-suited for low-frequency vibrations and posture changes.
Frequency Range: Handles frequencies from a few mHz to several kHz, suitable for detecting low-frequency and static movements, such as in structural vibration analysis. For instance, Analog Devices’ ADXL335 can measure from 0 Hz to 1600 Hz.
Price Range: $35 to $700. Capacitive accelerometers are widely used in consumer electronics to high-precision industrial applications.
Sensitivity: From 1 mV/g to 500 mV/g, with sensitivity varying by application; high-sensitivity models support precise measurements.
Temperature Range: Operates reliably between -40°C and +85°C, with temperature compensation ensuring minimal sensitivity fluctuations.
Non-Linearity: Below 0.2%, offering high accuracy for static acceleration and low-frequency applications, suitable for posture control and motion sensing.
Example: The Analog Devices ADXL335 is widely used in smartphones, game controllers, and wearables for its small size and low power consumption.
Advantages: Capable of measuring static acceleration, making it suitable for consumer applications like smartphones and wearables with high cost-effectiveness.
Disadvantages: Not ideal for high-frequency measurements and can be sensitive to noise, necessitating filtering. Also susceptible to humidity and temperature changes.
Mounting Method: Typically mounted with tape or adhesives, or with screws and clamps when additional stability is needed.
Output Signal Type: Outputs an analog voltage signal corresponding to capacitance changes, allowing measurement of both static and dynamic acceleration. Digital output models are also available, compatible with protocols like I²C and SPI.
Calibration: Both static and dynamic calibration is possible. Static calibration involves aligning the sensor to a 1 g gravitational acceleration, while dynamic calibration uses a known vibration source.

3. Piezoresistive Accelerometer

Operating Principle: Piezoresistive accelerometers detect acceleration based on resistance changes in an internal piezoresistive element when force is applied. This resistance change is converted to an electrical signal, reflecting the acceleration. It’s suitable for precise measurement of static acceleration and low-frequency vibrations, commonly used for impact detection in vehicles and machinery monitoring.
Frequency Range: Ranging from 0 Hz to several kHz, excellent for static and low-frequency vibration measurements. Kistler's PiezoBeam series offers a wide frequency range for impact and vibration analysis.
Price Range: $70 to $2,100, depending on the application, from general automotive to high-precision industrial use.
Sensitivity: Moderate, from a few mV/g to 500 mV/g, suitable for impact and low-frequency measurements.
Temperature Range: Temperature-sensitive; some models include temperature sensors for compensation, stable within -40°C to +85°C.
Non-Linearity: From 0.1% to 1%, ensuring high accuracy for low-frequency and static acceleration, ideal for impact detection.
Example: Kistler PiezoBeam series is widely used for impact measurement in automotive and sports performance analysis, featuring durability and temperature compensation.
Advantages: Capable of static acceleration measurement with stable performance if properly temperature-compensated, ideal for low-frequency vibration.
Disadvantages: Unsuitable for high-frequency measurements, with potential accuracy issues without adequate temperature compensation.
Mounting Method: Requires careful mounting, usually via screws or adhesives, with torque guidelines for stability.
Output Signal Type: Outputs an analog voltage signal based on resistance changes, typically low voltage, requiring amplification.
Calibration: Both static and dynamic, with periodic recalibration recommended.

4. MEMS (Micro-Electro-Mechanical System) Accelerometer

Operating Principle: MEMS accelerometers measure acceleration using tiny mechanical structures. Internal movable masses change capacitance in response to acceleration, outputting an electrical signal. MEMS sensors are compact, energy-efficient, and measure 3-axis acceleration, popular in smartphones and fitness trackers.
Frequency Range: 0 Hz to several kHz, ideal for low to medium frequencies, with 3-axis measurement capabilities. Bosch Sensortec BMA400, for example, offers accurate readings from 0.25 Hz to 1500 Hz.
Price Range: Ranges from around $1 to $25; consumer-grade models are very affordable, with industrial-grade units costing slightly more.
Sensitivity: 300 mV/g to 5000 mV/g, highly sensitive to subtle motions, ideal for mobile devices.
Temperature Range: Operates within -40°C to +85°C, typically with temperature compensation for stable readings.
Non-Linearity: Low, around 0.1% to 0.5%, suitable for motion detection in mobile and IoT devices.
Example: Bosch Sensortec BMA400 is widely used in wearables and IoT, offering high-precision and low-power operation.
Advantages: Small, affordable, and ideal for consumer devices, with low power consumption.
Disadvantages: Less suitable for industrial applications requiring high precision and sensitive to noise.
Mounting Method: Often surface-mounted on circuit boards; can also be mounted with adhesive or screws.
Output Signal Type: Outputs analog or digital signals (I²C, SPI), widely compatible with microcontrollers.
Calibration: Static and dynamic, with calibration performed for each axis.

5. Servo Accelerometer

Operating Principle: Servo accelerometers measure acceleration by detecting the displacement of an internal inertial mass, which is controlled by a feedback current proportional to the acceleration. They are ideal for low-frequency, high-precision applications like seismic monitoring and structural health systems.
Frequency Range: 0 Hz to several hundred Hz, ideal for static acceleration with high accuracy. Honeywell QA6500 series can measure low-frequency vibrations from 0.001 Hz to 100 Hz.
Price Range: $350 to several thousand dollars, with high-end seismic and aerospace models at the upper range.
Sensitivity: 1 V/g to 10 V/g, extremely high, suitable for detecting minute acceleration changes.
Temperature Range: Operates from -55°C to +85°C with stability, suitable for long-term monitoring.
Non-Linearity: Below 0.01%, providing stable, long-term measurements, ideal for seismic and structural monitoring.
Example: Honeywell QA6500 series is commonly used in seismic and structural monitoring, featuring high precision and durability.
Advantages: High precision and long-term stability, ideal for low-frequency applications in seismic and structural monitoring.
Disadvantages: Expensive, unsuitable for high-frequency changes.
Mounting Method: Requires secure attachment, typically with screws or adhesives, to ensure accurate measurements.
Output Signal Type: Analog voltage output, providing high-resolution signals for precise applications.
Calibration: Mainly dynamic, using known acceleration to confirm specifications, with periodic recalibration recommended.

6. Hall Effect Accelerometer

Operating Principle: Hall effect accelerometers detect acceleration by measuring changes in magnetic fields caused by the movement of internal components. This non-contact measurement is ideal for static acceleration and slow movement, commonly used in robotics and automotive driver assistance.
Frequency Range: 0 Hz to several hundred Hz, effective for static and low-frequency measurements. Allegro MicroSystems A1330 can measure static acceleration over a broad temperature range.
Price Range: $70 to $700, varying by precision and application.
Sensitivity: From tens to hundreds of mV/g, suitable for posture control in robotics and automotive systems.
Temperature Range: Operates between -40°C and +150°C with temperature stability.
Non-Linearity: Below 0.5%, providing high accuracy for posture control and robotics applications.
Example: Allegro MicroSystems A1330 is widely used for high-precision posture control in industrial equipment and robotics.
Advantages: Non-contact measurement suitable for long-term monitoring, high precision for static acceleration in industrial and automotive applications.
Disadvantages: Not suitable for high-frequency vibration or impact measurement; sensitive to temperature and magnetic field changes.
Mounting Method: Requires precise positioning and secure attachment to minimize external magnetic field impact.
Output Signal Type: Typically analog, but digital models also exist.
Calibration: Both static and dynamic calibration possible, with vibration tests to confirm sensor accuracy and sensitivity adjustments as needed.