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Capacitive sensors

Category: مطالب آموزشی "Educational materials" Date: 2025 August 04

Capacitive sensors

Capacitive sensors are non-contact and non-electrical-contact sensors that can detect metals as well as most non-metals. They are suitable for level control in tanks filled with powdered, liquid or granular materials.

They can also be used as pulse generators for monitoring machine program status, for counters, and for detecting almost all metallic and non-metallic materials.

Operation:

The basic structure of these sensors consists of four parts.

The core part of the oscillator consists of two metal plates positioned in such a way that they form a capacitive element. When an object approaches the sensing surface, it changes the dielectric constant (E) of the capacitive field between the plates. This change in capacitance alters the output amplitude of the oscillator.

The demodulator detects the amplitude of the oscillator and compares it with a reference level. When the measured amplitude exceeds the reference threshold, the sensor output is activated.

The output amplifier is responsible for supplying the load current.

These sensors are manufactured in the following types:

  • Two-wire AC
  • Three-wire NPN and PNP
  • Four-wire NPN and PNP

Application:

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