Motion Sensor - a device that allows you to identify any movement in the area of responsibility. The logic level of digital electronics is usually used as a response signal. As a result, it becomes possible to detect the presence of movement within the alarm systems, lighting, automatic door control, etc.
Varieties and operating principles of motion sensors
Passive infrared motion sensors
In the domestic literature, more often it comes to passive infrared motion sensors( PIR).This product category has a number of drawbacks. Usually, a passive infrared sensor works on the basis of the pyroelectric effect: it feels warm from a distance. Developers, as a rule, adjust to the temperature of the human body and catch the waves of the middle infrared range around 10 microns. This is much lower than the visible radiation, a film with the participation of the great Arnie and the hunt for the Predator. The newcomer sensory system responded to the waves of the thermal range.
For this reason, it is possible to deceive the passive infrared sensor. Similar in serious alarm systems are not used. A pyroelectric motion sensor contains a crystal that converts the specified wavelength to an electric charge. To eliminate interference at the entrance is a filter in the form of a lens made of silicone. It severely limits the range of incoming radiation, for example, from 7 to 15 microns, reducing the level of external interference.
As a rule, the system consists of two parts in order to simultaneously register external background. The chip window, which transmits radiation, is divided into two equivalent parts, each looking toward the center. As a result, if a moving warm body is in sight of the window, the difference will immediately become apparent. The developers claim that, thanks to Fresnel lenses, a power of about 1 µW will suffice to get a response. In light of the above, most passive infrared motion sensors require no training time. For a short period in the field of view of the lenses should not fall moving objects.
The period lasts up to a minute, then it is permissible to use a motion sensor. The principle of signal transmission varies. As a rule, a manufacturer within the series of microcircuits produces a sensor and an appropriate multifunctional controller, with tasks for working with the accompanying type of equipment. This makes it possible to create complex systems. The level corresponds, for example, to a logical CMOS unit, or it produces a series of pulses of a specified frequency. Known passive infrared sensors, with the ability to customize the specified parameter, which makes the chip more flexible.
Inside there is an amplifier for forming the desired response. This requires supplying power from the outside. The connector scheme is extremely simple:
- Leg power.
- Grounding( circuit zero).
- Information signal output.
Sensor Design Disadvantages of Passive Infrared Motion Sensors
Anyone familiar with electronics is aware of the shortcomings of the sensors described above: radiation is easily shielded. It is enough to place a solid object in the field of view of the sensor to interfere with the performance of the system. Thermal radiation will cease to reach the sensing element. A dressed person, for example, forms a much smaller response.
In addition, the range is limited. Determined by the sensitivity of the element and the force of thermal radiation of the object. In most cases - read meters, which imposes restrictions on use.
The temperature of the medium is of great importance. As it decreases, the temperature pattern will begin to fall on the frequency scale, distorting the sensitivity of the sensor. The option is considered controversial when the first sensor window looks out onto the street, and the second into the room. We have to focus on the recommendations of the manufacturer on the conditions of use.
Laser sensors are known in the film banks. This is a technique for fixing movement on a straight line. A radiation source and receiver are placed opposite each other. When an object gets between them, an alarm is generated. The laser is sometimes invisible, the use of special cartridges with gas, luminous under the action of infrared or ultraviolet rays, not the invention of filmmakers. The phenomenon of luminescence is used to determine the location of invisible paths.
As the wavelength increases, the directional properties of the radiation drop sharply, radio bands do not apply as rays anymore. As for high frequencies that can pass through obstacles like x-rays, they are not suitable for use, for obvious reasons.
Sensors on the Doppler effect
The group includes two families separately: ultrasonic and microwave motion sensors. The principle of action is based on a single effect. Doppler discovered the phenomenon in 1842, observing systems of binary stars and other celestial bodies. Three years later, Buis-Ballot proved that spectrum shift is also observed for sound sources.
Each resident of the capital and the inhabitants of other major cities noticed that the horn of the approaching electric train is higher than the receding. Thus, a person who is more or less gifted musically is able to determine whether the train is approaching the platform or is running away. This is the Doppler effect: any wave emitted by an object is perceived by a fixed observer in accordance with the mutual speed of movement. The speed depends on the magnitude of the shift in the spectrum.
The retreating star seems a bit colder than it really is: the spectrum will move down the frequency scale. On the contrary - the color approaching looks warmer. A similar effect is observed in any range: radio, sound and others. Readers have already guessed how the sensors on the Doppler effect work. An oscillation of ultrasound or radio frequency is emitted into the ether, the response is caught. In the presence of moving objects, the picture changes radically: instead of a homogeneous radiated wave, a whole host is taken that differs in frequency from the original one.
Plus method: radiation easily bends around obstacles or passes through. But the movement is recorded in relation to any objects, including inanimate. Body temperature does not matter. The frequency of the radiation depends on the characteristics of the system. For example, the radio band for the most part is prohibited for use. Left small windows, edited by a special state committee. Ultrasound has no limitations, but is harmful to human hearing( even if it is not directly felt).For example, repellents for dogs and cockroaches function in the specified range.
are used. Thus, ultrasound and radio frequency motion sensors are much more difficult to screen.
Tomographic motion sensors
The word resembles medical equipment, according to the developers, means that there is a grid in the system of active transmitters. The complex operates in the allowed 2.4 Hz range, where WiFi modems, microwave ovens and a number of devices operate. What immediately imposes restrictions: in the field of view of the system, it is intended to limit the use of the products listed above.
The effect is based on the well-known absorption of radiation at a frequency of 2.4 Hz by water molecules. The body of a living creature is the most common liquid on the planet enters in excess, making it possible to build a picture indoors.2.4 Hz waves pass through walls relatively easily, it is possible to cover relatively large areas of complex configuration. A network of transceivers is mounted on the ground, like WiFi access points.
A sophisticated computer system analyzes field distribution. The training stage is implied when the conditions of wave propagation in a specific room are evaluated. In the future, according to special algorithms, the system is able to indicate the location of any bodies in space. It is possible to detect and motionless living bodies. When the biological form of life falls within the range of the waves, their strength begins to fade according to certain laws. Energy goes into heat, as happens in a microwave. As a result, it becomes possible to generate an alarm.
Emitters are not dangerous to humans, and the working power is regulated in accordance with the law. The local administrator is requested, starting from a certain size, to register the system in the prescribed manner. Sensors are more expensive than other ones presented in the review. Doppler also cost a lot.
Sensor Operation Video Cameras as
Sensors Today, most digital video cameras detect the option of capturing motion. It is possible to record a signal to the recorder, alarm in the prescribed manner. The sensor is quite enough for the needs of the organization. The registration process, the start and end of the event fixation is determined by the capabilities of the individual equipment.
A big plus for the system is the ability to act in automatic mode and the chance to record illegal actions if necessary. The only obstacle is considered the law on the privacy of citizens. It is proposed to clearly distinguish illegal actions from others. And do not distribute the information obtained in circumvention of the law.
For work in the dark, infrared recorders are used with the indispensable illumination of the surrounding landscape. There are manuals on the Internet where it is proposed to make an infrared recorder from the camera's viewfinder for night shooting. The backlight is assembled on the basis of conventional infrared diodes. The shooting range in this case is strongly dependent on the power of infrared rays. For the purpose of amplification, it is recommended to use reflectors.
The use of motion sensors
Often the use of motion sensors encounters certain limitations. Passive infrared sensors in this regard, the simplest, their use is not standardized. Where ultrasounds and radio waves begin - it is proposed to carefully calculate the consequences. Lasers are not safe, a warning label on a laser printer is not a joke. Coherent radiation burns through the retina no worse than paper, causing serious injury.
Closely associated with motion sensors for detecting the presence of smoke in a room. In this case, the phenomena of changing the conditions of passage of radiation, plus the Doppler effect, are used. Pure chemical techniques are quite rare.
Motion sensors are used in the following systems:
- alarms and guards;
- door control;
- entertainment complexes;
The range of application depends only on the authors' imagination; therefore, foreign manufacturers also produce integrated systems with the possibility of embedding them in more complex ones. So, to cover a certain area, it is permissible to dial a set of sensors like a designer. The tomography systems have the greatest flexibility in this regard, but they are also more expensive. The simplest infrared sensors are more suitable for controlling single objects, for example, doors.