THE CAPACITIVE ACCELEROMETER


How do Capacitive Accelerometers - Vibration Sensors work ?
Capacitive accelerometers (vibration sensors) sense a change in electrical capacitance,
with respect to acceleration, to vary the output of an energized circuit.
The sensing element consists of two parallel plate capacitors acting in a differential mode.

These capacitors operate in a bridge circuit, along with two fixed capacitors, and alter the peak voltage generated by an oscillator when the structure undergoes acceleration. Detection circuits capture the peak voltage, which is then fed to a summing amplifier
that processes the final output signal.


Structure of Capacitive Accelerometers
Capacitive accelerometers sense a change in electrical capacitance, with respect to acceleration, to vary the output of an energized circuit.

When subject to a fixed or constant acceleration, the capacitance value is also a constant, resulting in a measurement signal proportional to uniform acceleration, also referred to as DC or static acceleration.

PCB’s capacitive accelerometers are structured with a diaphragm, which acts as a mass that undergoes flexure in the presence of acceleration. Two fixed plates sandwich the diaphragm, creating two capacitors, each with an individual fixed plate and each sharing the diaphragm as a movable plate. The flexure causes a capacitance shift by altering the distance between two parallel plates, the diaphragm itself being one of the plates.

The two capacitance values are utilized in a bridge circuit, the electrical output of which varies with input acceleration.

Article by PCB Piezotronics Inc



 
 
Micromachined Silicon Variable Capacitance Accelerometers
Design and Application
A 5-page technical article by Tom Connolly of Endevco Corp.
To view complete pdf file, click
here



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