Proximity sensor: features and capabilities
In everyday life, the proximity sensorit is used almost everywhere. On cars it helps with parking, on conveyors tracks the movement of products, in modern phones it blocks the keyboard after putting the device to your ear. In everyday life this miracle of technology also found its place. Such devices are installed in place of a switch, say, on the street. As soon as you approach the house, the light automatically turns on, and after a while it turns off. In security systems in general, it is impossible to do without sensors.
There are proximity sensors by types:capacitive, inductive, optical, ultrasonic, microwave, magnetosensitive, pyrometric, etc. The kind of device that a particular device belongs to depends on the principle of its operation.
The capacitive proximity sensor is used inmostly in security systems, because he discovers the approach of the object and can not miss it. This distinguishes it from ultrasonic or infrared analogs, the operating distance of which strongly depends on the surface of the object. For example, the infrared proximity sensor reacts to thermal infrared rays. Ultrasonic devices first emit, and then receive reflected from the surface of the rays. According to the principle of operation, this proximity sensor is very similar to a locator. And like everything is not bad, from solid surfaces the signal is reflected well, but from the soft - not very. And the intruder can bypass it, just putting on something soft. It is for these reasons that it is best to use capacitive type sensors, especially in signaling devices, for protecting 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 capacitor of small capacity.
Capacitive sensors are also of several types:
1. Sensors on capacitors.It is the circuits of the latter that are a sensitive part of this device. This type is used where there is no need for noise immunity and high sensitivity, for example, in signaling devices that touch metal objects.
2.Capacitive sensors that use a frequency-setting circuit. This type of device is less susceptible to radio 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 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. Resonance-capacitive sensors.The trip 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 by means of a capacitor of small capacity (the element necessary for resistance in the circuit). Such sensors can be used both in field, rural, and urban environments, but not very close to powerful sources of radio signals.