Page 115 - Sensors and Control Systems in Manufacturing
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FIGURE 2.61 Capacitive principle.
FIGURE 2.62 Capacitive sensor.
Figure 2.62 illustrates the principle as it applies to the capacitive
sensor. One capacitive plate is part of the switch, the sensor face (the
enclosure) is the insulator, and the target is the other plate. Ground is
the common path.
The capacitive proximity sensor has the same four basic elements
as an inductive proximity sensor:
• Sensor (the dielectric plate)
• Oscillator circuit
• Detector circuit
• Solid-state output circuit
The oscillator circuit in a capacitive switch operates like one in an
inductive proximity switch. The oscillator circuit includes feedback
capacitance from the external target plate and the internal plate. In a
capacitive switch, the oscillator starts oscillating when sufficient
