27-09-2012, 11:26 AM
PIR-based motion detector
[attachment=34577]
Operating principles
All objects above absolute zero emit heat energy in the form of infrared radiation (infrared light). Usually infrared light is invisible to the human eye, but it can be detected by electronic devices designed for such a purpose.
The term passive in this instance refers to the fact that PIR devices do not generate or radiate any energy for detection purposes. They work entirely by detecting the energy given off by other objects.[1]
Construction
Infrared radiation enters through the front of the sensor, known as the sensor face. At the core of a PIR sensor is a solid state sensor or set of sensors, made from pyroelectric materials -- materials which generate energy when exposed to heat. Typically, the sensors are approximately 1/4 inch square, and take the form of a thin film. Materials commonly used in PIR sensors include gallium nitride (GaN),caesium nitrate (CsNO3), polyvinyl fluorides, derivatives of phenylpyrazine, and cobalt phthalocyanine. The sensor is often manufactured as part of an integrated circuit.
Operation
Strictly speaking, individual PIR sensors do not detect motion; rather, they detect abrupt changes in temperature at a given point. As an object, such as a human, passes in front of the background, such as a wall, the temperature at that point will rise from room temperature to body temperature, and then back again. This quick change triggers the detection. Moving objects of identical temperature will not trigger a detection.[1][2][3][4][5][6][7]
PIDs can be equipped with more than one internal sensing element so that, with the appropriate electronics, it can detect the apparent direction of movement. As an object passes in front of adjacent sensors in turn, this implies the direction of movement. This may be used by on-board electronics to reduce false alarms, i.e., by requiring adjacent sensors to trip in succession. It may also be used to signal the direction of movement to a monitoring apparatus.
PIDs come in many configurations for a wide variety of applications. The most common models have numerous Fresnel lenses or mirror segments, an effective range of about thirty feet, and a field of view less than 180 degrees. Models with wider fields of view, including 360 degrees, are available -- typically designed to mount on a ceiling. Some larger PIDs are made with single segment mirrors and can sense changes in infrared energy over one hundred feet away from the PID. There are also PIDs designed with reversible orientation mirrors which allow either broad coverage (110° wide) or very narrow "curtain" coverage, or with individually selectabl
[attachment=34577]
Operating principles
All objects above absolute zero emit heat energy in the form of infrared radiation (infrared light). Usually infrared light is invisible to the human eye, but it can be detected by electronic devices designed for such a purpose.
The term passive in this instance refers to the fact that PIR devices do not generate or radiate any energy for detection purposes. They work entirely by detecting the energy given off by other objects.[1]
Construction
Infrared radiation enters through the front of the sensor, known as the sensor face. At the core of a PIR sensor is a solid state sensor or set of sensors, made from pyroelectric materials -- materials which generate energy when exposed to heat. Typically, the sensors are approximately 1/4 inch square, and take the form of a thin film. Materials commonly used in PIR sensors include gallium nitride (GaN),caesium nitrate (CsNO3), polyvinyl fluorides, derivatives of phenylpyrazine, and cobalt phthalocyanine. The sensor is often manufactured as part of an integrated circuit.
Operation
Strictly speaking, individual PIR sensors do not detect motion; rather, they detect abrupt changes in temperature at a given point. As an object, such as a human, passes in front of the background, such as a wall, the temperature at that point will rise from room temperature to body temperature, and then back again. This quick change triggers the detection. Moving objects of identical temperature will not trigger a detection.[1][2][3][4][5][6][7]
PIDs can be equipped with more than one internal sensing element so that, with the appropriate electronics, it can detect the apparent direction of movement. As an object passes in front of adjacent sensors in turn, this implies the direction of movement. This may be used by on-board electronics to reduce false alarms, i.e., by requiring adjacent sensors to trip in succession. It may also be used to signal the direction of movement to a monitoring apparatus.
PIDs come in many configurations for a wide variety of applications. The most common models have numerous Fresnel lenses or mirror segments, an effective range of about thirty feet, and a field of view less than 180 degrees. Models with wider fields of view, including 360 degrees, are available -- typically designed to mount on a ceiling. Some larger PIDs are made with single segment mirrors and can sense changes in infrared energy over one hundred feet away from the PID. There are also PIDs designed with reversible orientation mirrors which allow either broad coverage (110° wide) or very narrow "curtain" coverage, or with individually selectabl