Contact and infinite switches can be effectively used as probes for recording the position of objects. The simplest of these converters is a micro working with poor physical connection between him and the object, the position of which it defines. As for proximity sensors, they do not have a physical connection with the objects. The presence of the body they are judged by a particular principle of detection is implemented in the respective converters
In inductive proximity sensor uses customized generator. When conducting body closer to the sensor, there is a damping of the oscillations, the perceived pattern of conjugation. More common and simple devices are inductive switches approximation, in which the use of interface circuit is turned on or off at the approach to them conducting body.
Capacitive proximity sensors are performed either as transmitters or in the form of circuit breakers. Their operating principle is that what is next body changes dielectric capacitor, so that is the imbalance of the bridge, one arm of which is located said capacitor. Capacitive sensors are more inductive, but they are able to perceive the approach of bodies made of different materials in a wide range of distances.
There are also a large number of optical sensors for the proximity. They consist of a basic sensor and its interface circuit to the measuring system. In these devices are implemented two ways to define the approximation straight (direct) or scan and reflection (Fig. 1). Reflective sensors can be retroreflektivnymi (Fig. 1a), the light source and the sensor are placed together, and the emitted light is reflected back and passes along the same path as the incident. In a mirrored device (proximity sensor) (Fig. 1b) of the source of the beam and the reflected beam of light are at an angle to each other and are reflected from the surface of the body as a mirror. In diffuse sensor uses transmission of light through a matte surface of the body (Fig. 1, B).
Magnetic proximity sensors are quite common instruments and incorporate reed switch or Hall sensors.
Radar proximity sensors consist of a radar signal generator and mixer, in which the interaction of the probe and the reflected signals. When using the Doppler effect (the frequency of the reflected signal is different from the frequency of the signal, when the body moves), the output frequency mixer is zero when the body does not move, and is different from zero, if it starts to move. Most of these proximity sensors operate in the X-rays.
The application of these devices (proximity sensor) is not limited to the measurement of displacement. The sensors can detect and distance, and hence the speed by determining the time between the transmitted and reflected pulses and perform the necessary calculations with the results of these measurements.
Fig. 1. The principles of operation of optical devices (sensors, transducers) to determine