Book Analog Interfacing to Embedded Microprocessors
to provide the bias.
Motion/Acceleration Sensors
Sometimes you need to measure acceleration or tilt or other motion. The
obvious application is airbag deployment in a car. However, there are other
applications, such as sensing vibration that could indicate excessive bearing
wear or an unbalanced load in a motor-driven application.
Solid-state acceleration sensors use internal capacitors to measure this
force (Figure 3.28). A micromachined movable beam and two fixed plates are
used. The movable beam has a spring that keeps it centered between the two
fixed plates when there is no acceleration. The two fixed plates are driven
with a signal from an oscillator. The two plates get the same signal, but 180°
86 Analog Interfacing to Embedded Microprocessors
Figure 3.28
Solid-state acceleration sensor.
out of phase with each other. The resulting voltage at the movable beam is
zero
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