How Inductive Proximity Sensors work

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Inductive proximity sensors work by using electromagnetic fields, so they can only detect metallic targets. When a metal target enters an electromagnetic field, the inductive properties of the metal change the properties of the magnetic field, alerting the proximity sensor of the presence of the metal target. Depending on how sensitive the metal is, targets can be detected at greater or shorter distances. An inductive proximity Sensor consists of four main parts: a ferrite core with a coil, an oscillator, a Schmitt trigger, and an output amplifier.

The oscillator generates a symmetrical oscillating magnetic field that emanates from a ferrite core and an array of coils at the sensing face. When an iron target enters this magnetic field, small independent currents called eddy currents are generated on the metal surface. This changes the reluctance (natural frequency) of the magnetic circuit, which in turn reduces the oscillation amplitude. As more metal enters the induction field, the amplitude of the oscillations decreases and eventually collapses. (This is the "eddy current suppressed oscillator" or ECKO principle.) The Schmitt trigger responds to these amplitude changes and adjusts the sensor output. When the target finally leaves the range of the sensor, the circuit starts to oscillate again and the Schmitt trigger returns the sensor to its previous output.

Due to the limitation of the magnetic field, the sensing range of the inductive sensor is relatively narrow, ranging from a few millimeters to 60 millimeters on average. But what inductive sensors lack in range, they make up for in environmental adaptability and the diversity of metal sensing.

Since there are no moving parts to wear out, inductive proximity sensors have a long service life. Be aware, however, that metal contaminants such as files in cutting applications can sometimes affect sensor performance, so inductive sensor housings are typically nickel-plated brass, stainless steel, or PBT plastic.

Four-step selection method for proximity sensors~

The seemingly ordinary proximity sensor is actually very particular. Correct selection and use are crucial to improving the reliability and stability of the device. There are many aspects to be considered in the selection, and the specific choice should be made flexibly according to customer requirements and site conditions. Generally, the following conditions can be considered.

1. The material of the measured object

First of all, determine the material of the object to be tested. The material is metal, and both capacitive and inductive types can be detected. For non-metallic objects, capacitive types need to be selected.

2. The influence of material on detection distance

Select a sensor with a suitable range according to the detection distance requirements. Pay attention to the influence of different materials to be measured on the sensor detection distance. For example, for the inductive type, the attenuation factor of the material should be considered, and for the capacitive type, the influence of the dielectric constant of the material should be considered.