Proximity sensor: features and capabilities

In everyday life, the proximity sensorused almost everywhere. On cars, it helps with parking, on conveyors it tracks the movement of products, in modern phones it blocks the keyboard after applying the device to the ear. In everyday life, this miracle of technology also found its place. Such devices are installed instead of the switch, for example, on the street. As soon as you come to the house, the light automatically turns on, and after a while it turns off. In security systems, it is generally impossible to do without sensors.

Distinguish proximity sensors by type:capacitive, inductive, optical, ultrasonic, microwave, magnetically sensitive, pyrometric, etc. What type a particular device belongs to depends on how it works.

Capacitive proximity sensor is used inmainly in security systems, because it detects an approaching object and can not miss it. This distinguishes it from ultrasonic or infrared analogs, the distance of which depends strongly on the surface of the object. For example, an infrared proximity sensor responds to heat - infrared - rays. Ultrasonic devices first emit and then receive the rays reflected from the surface. By the principle of operation, this proximity sensor is very similar to a locator. And everything seems to be quite good, the signal is reflected well from hard surfaces, but not very well from soft ones. And the offender can bypass it, just putting on something soft. For these reasons, it is best to use sensors of the capacitive type, especially in alarm devices, for the protection of important and large objects. In this case, the antenna in the form of wires horizontally attached to the fence and connected to the main device through a capacitor of small capacity.

Capacitive sensors are also of several types:

1. Sensors on capacitors.The latter schemes 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.

2Capacitive sensors using a frequency reference circuit. This type of device is less susceptible to radio interference and interference than devices with capacitors. This type 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, rather than one, which provides for the suppression of the effects of weather (rain, snow, thunderstorms, hoarfrost, etc.). Their field of application does not differ from the sensors on the LC circuit. The only difference is that you need to install another antenna.

4. Резонансно-емкостные датчики.The trigger signal occurs in the input circuit, which is in a partially unbalanced state with respect to the signal of the high-frequency generator. With it, the circuit is connected with a small capacitor (an element necessary for resistance in the circuit). Such sensors can be used both in field, rural, and in urban environments, but not very close to powerful radio sources.