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Operating principles for capacitive sensor

Capacitive proximity sensors are used for non-contact detection of metallic objects & nonmetallic objects (liquid, plastic, wooden materials and so on). Capacitive proximity sensors use the variation of capacitance between the sensor and the object being detected. When the object is at a preset distance from the sensitive side of the sensor, an electronic circuit inside the sensor begins to oscillate. The rise or the fall of such oscillation is identified by a threshold circuit that drives an amplifier for the operation of an external load. A screw placed on the backside of the sensor allows regulation of the operating distance. This sensitivity regulation is useful in applications, such as detection of full containers and non-detection of empty containers. The operating distance of the sensor depends on the actuator shape and size and is strictly linked to the nature of the material.

(Table 1)

Table 1. Sensitivity when different materials are present. Sn = operating distance.
Metal ~ 1 x Sn
Water ~ 1 x Sn
Plastic ~ 0.5 x Sn
Glass ~ 0.5 x Sn
Wood ~ 0.4 x Sn
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