sensors 2


Accelerometers are integrated circuits or modules used to measure the acceleration of an object to which they are attached. They are used in applications including: vehicle dynamics, mobile phone orientation detection, image stability, tilt, tap detection and anti-theft devices. Accelerometers are available in a number of technologies including: piezoelectric, piezoresistive and variable capacitance.

Variable capacitance accelerometers are available in a number of configurations including vibration sensors based upon a tunable oscillator circuit and micro electrical mechanical systems (MEMS). Tunable oscillator circuits incorporate a capacitor with a plate that acts as a moving diaphragm-like mass relative to other fixed plates. Acceleration causes the diaphragm to flex, creating a capacitive shift. This changes the peak voltage of oscillation. MEMs accelerometers are implemented as a variable capacitor changed by a cantilevered beam connected to a proof-mass. They are available in devices that support 1 to 3 axes. MEMS accelerometers utilize serial interfaces like I2C and SPI. They have high linearity and are best used in low frequency applications.

Piezoelectric accelerometers derive acceleration from the voltage generated by piezoelectric effects occurring in ceramic or crystal piezoelectric material. A voltage is produced when the inertia of an attached mass under acceleration stresses the material. Piezoelectric devices have high frequency range and high temperature range. They are the best choice for measuring vibration and are used in many scientific and industrial applications like process control.
Piezoresistive accelerometers derive acceleration from resistance changes generated by piezoelectric effects in piezoelectric material. Resistance changes when the inertia of an attached mass under acceleration stresses the material. Piezoresistive sensors output a voltage proportional to their resistance. Devices are available as either MEMs or bonded strain-gauge types. They are preferred in high frequency, high accuracy and high g shock applications. They are found in applications like automobile breaking systems, safety airbags and seismic measurement.

Acceleration range is a very important consideration for accelerometers. This is specified as a ratio of +/-‘g’s – that is acceleration due to gravity or 9.80665 m/s2. Sensitivity is also important and is usually limited by the integrated analog to digital converter (ADC) bit precision. They have a passband characteristic on their acceleration measurement that specifies the lowest and highest acceleration that can be measured. The maximum sample rate determines how accurately the accelerometer can measure instantaneous acceleration or the rate of change of the same. Rate of change of acceleration is referred to as a jerk, jolt, surge or lurch.
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