In everyday life, the proximity sensor is used almost everywhere. On cars, it helps with parking, on the conveyors it tracks the movement of products, in modern phones it locks the keyboard after attaching the device to the ear. In everyday life, this miracle of technology also found its place. Such devices are installed instead of a switch, for example, on the street. As soon as you approach the house, the light automatically turns on, and after a while turns off. In security systems it is generally impossible to do without sensors.
Distinguish proximity sensors by type: capacitive, inductive, optical, ultrasonic, microwave, magnetosensitive, pyrometric, etc. What kind of particular device belongs to depends on the principle of its operation.
A capacitive proximity
sensor is mainly used in security systems, because it detects the proximity of an object and cannot miss it in any way. This distinguishes it from ultrasonic or infrared counterparts, the response distance of which greatly depends on the surface of the object. For example, an infrared proximity sensor responds to thermal - infrared - rays. Ultrasonic devices first emit and then receive rays reflected from the surface. By the principle of operation, this proximity sensor is very similar to a locator. And everything seems to be fine, the signal reflects well from hard surfaces, but not very from soft surfaces. And the intruder can get around him, just putting on something soft. For these reasons, it is best to use capacitive-type sensors, especially in alarm devices, to protect important and large objects. In this case, the antennas in the form of wires are horizontally attached to the fence and connected to the main device through a small capacitor.
Capacitive sensors are also of several types:
1. Sensors on capacitors. It is the circuits of the latter that are the sensitive part of this device. This type is used where noise immunity and high sensitivity are not needed, for example, in signaling devices that touch metal objects.
2. Capacitive sensors using a frequency response loop. This type of device is less susceptible to interference and interference than devices with capacitors. This kind can be used in everyday life to turn on lighting, etc.
3. Differential-capacitive sensors. They differ from the above in that they have two antennas, and not one, which provides suppression of the effects of weather (rain, snow, thunderstorms, hoarfrost, etc.). Their field of application does not differ from sensors on the LC circuit. The only difference is that you need to install another antenna.
4. Resonance-capacitive sensors. The response signal occurs in the input circuit, which is in a partially unbalanced state with respect to the signal of the high-frequency generator. A circuit is connected to it using a small capacitor (an element necessary for resistance in a circuit). Such sensors can be used both in field, rural, and in urban conditions, but not very close to powerful sources of radio signals.