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Capacitive Transducer Function

– utilize capacitance change
• due to changes in the position of the dielectric material between the two pieces
• due to the shifting position of one of the pieces and the area of ​​the face-to-face
• due to the addition of distance between the two keeping

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Figure 3.31 Capacitive position sensor: (a) horizontal media shift, (b) rotary shift, (c) shifting plate distance

– the capacitance value is directly proportional to the area and is proportional to the distance

C = 0.0885 d A k

– quite sensitive but bad linearity
– bridge circuit as in inductive sensor can be used with capacitor connected parallel with high resistance to give DC path for opamp input
– the second alternative changes the capacitance change to the oscillator frequency change
• center frequency 1 – 10 MHz
• frequency change for capacitance change is quite small compared to Co capacitance
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Figure 3.32 Position sensor use in electronic circuit:
(a) the capacitance becomes frequency, (b) the capacitance becomes pulse

– Inexpensive circuit solution with dual inverter CMOS relaxation oscillator