Inductive sensors, also called eddy current sensors, consist of three major components: an oscillator, a switching circuit, and an amplifying output circuit. The oscillator produces an alternating magnetic field that, when the metal target approaches the magnetic field and reaches the sensing distance, creates eddy currents in the metal target, causing the oscillation to decay and even stop. The oscillation and oscillation of the oscillator are processed by the post-amplifier circuit and converted into a switching signal to trigger the drive control device to achieve non-contact detection.
Inductive proximity sensors are the core of oscillators and amplifiers for detecting metal objects. However, the attenuation of different metals, the standard object of detection is iron, but stainless steel, aluminum alloy, aluminum, copper, etc. will have different degrees of attenuation. It can be seen that the object that the proximity switch can detect must be an electrical conductor. Therefore, when selecting an inductive sensor, it must be confirmed with the customer and the engineer.
The capacitive proximity sensor is a sensor that has a switching output that can operate without mechanical contact with the object to be detected. The switch consists of high-frequency oscillation on the switch working surface and the target surface to be tested, which constitutes a capacitor connected to the same circuit in the oscillation, and participates in the oscillation circuit. When the detected object approaches the working surface of the switch, the capacitance of the circuit changes. This produces an opening and closing function to detect the presence or absence of an object. Due to the working characteristics of the capacitive proximity switch, the switch can not only detect metal, but also detect non-metallic substances such as plastic, glass, water, oil and the like. When detecting non-metallic objects, the corresponding detection distance is affected by the conductivity, dielectric constant, volumetric water absorption rate and other parameters of the object, and the corresponding detection distance is different. The maximum detection distance is given to the grounded metal conductor.
Similarly, capacitive proximity switches typically have an adjustable sensing range and different range variations for different materials. For example: water is 100%, alcohol is 70%, ceramic is 60%, glass is 50%, oil is 30%, etc.