A passive infrared sensor (PIR sensor) is an electronic sensor that measures infrared (IR) light radiating from objects in its field of view. They are most often used in PIR-based motion detectors. PIR sensors are commonly used in security alarms and automatic lighting applications.
Passive Infrared Detection: Theory and Applications
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PIR sensors are commonly called simply "PIR", or sometimes "PID", for "passive infrared detector". The term passive refers to the fact that PIR devices do not radiate energy for detection purposes. They work entirely by detecting infrared radiation (radiant heat) emitted by or reflected from objects.
PIRs 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 10 meters (30 feet), and a field of view less than 180. Models with wider fields of view, including 360, are available, typically designed to mount on a ceiling. Some larger PIRs are made with single segment mirrors and can sense changes in infrared energy over 30 meters (100 feet) from the PIR. There are also PIRs designed with reversible orientation mirrors which allow either broad coverage (110 wide) or very narrow "curtain" coverage, or with individually selectable segments to "shape" the coverage.
Active motion detectors using microwaves can cause false alarms, as the energy can penetrate most building materials. Hence, manufacturers have begun using the microwave technology in conjunction with passive infrared sensor technology.
A passive infrared sensor detects body heat (infrared energy) by looking for changes in temperatures. This is the most-widely-used motion sensor in home security systems. When you arm your system, this activates the motion sensors to report possible threats.
Some motion sensors can combine multiple detection methods in an attempt to reduce false alarms. For example, it's not uncommon for a dual technology sensor to combine a passive infrared (PIR) sensor with a microwave sensor.
Most passive infrared sensors can ignore animals up to a certain weight. A dual technology motion sensor is more pet resistant to false alarms because it requires two sensors to be triggered a certain way.
In contrast to the infrared (IR) detectors, which measure the radiation energy emitted from any object containing solid matter, that may represent an option for passive non-contact measurement of vital signs including respiration activity [13]. Resume to that, the skin is the largest organ of the human body and helps maintain the thermal equilibrium of the body and the environment through a heat transfer process.
Many physiological phenomena occur in the spectral band of long wave infrared (LWIR, 7 μ m to 14 μ m); however, in some bioheat transfer processes, these phenomena also take place in the range 3 μ m to 8 μ m mid-wave IR (MWIR) [13, 14] or in the range of 0.7 μ m to 2 μ m short-wave infrared (SWIR) [15]. For example, Pavlidis et al. [1, 20, 24] used MWIR sensors for distant measurement of cardiac and breathing rates in adults. In this work, the breathing measurements were based on heat transfer of the moisturized air during expiration, which is directly related to the respiration waveform. Although the exact shape is smoothed, it was shifted and noisy with respect to the actual respiration rate. Most probably, this is mainly due to the diffusion-convection heat transfer processes and air flow in the nasal cavity [7, 13, 17]. Note that the anatomical section of a nasal cavity (shown in Figure 5) also consists of vascular mesh, which contributes to the temperature conditioning of the inhaled air. As indicated, for breathing measurements, Palvidis et al. [1, 18, 20, 23, 24] used the expired and moisturized air flow to measure the respiration rate. As a result, the subject must have a sideview technique to the camera in order to visualize breathing-jet dynamics. Beside this side view orientation, Pavlidis also introduced the concept of nostrils tracking in adults [18, 20, 23]. Our method presented here is related to this concept, but differs in the spectral range. Also, signal processing was enhanced. While other groups [20, 23] used MWIR, our group used LWIR thermography, which is more stable in detection of temperature variance within the thermographic scenario [13, 15, 22]. In general, LWIR cameras are typically preferred for imaging applications that require absolute or relative measurements of object irradiance or radiance because emitted energy dominates the total signal in the LWIR. In the MWIR, extreme care is required to ensure the radiometric accuracy of data. Thermal references may be used in the scene to provide a known temperature reference point or points to compensate for detector-to-detector variations in response and improve measurement accuracy. This temperature reference measurement in our case is not possible, because this will include invasive nasal thermocouple and may interfere with our thermography image reading. Moreover, besides a characterization of the respiratorial behaviour, we focused on temperature changes in the nasal region (nostrils) within the thermal image to get possibly information about the impact on thermoregulation of the infants. Additionally, the thermal imaging was performed using both frontal and lateral views, in order to follow the defined region over the nostrils.
Basically, this type of thermographic imaging may be called "pulsed thermography", which implies that the process is repetitive in nature, which is true for the respiration rate. Therefore, it is essential to develop a method to detect a biphasic thermal breathing signal, which consists of two phases (active and passive states) [15, 20, 25]. Initially, during the application of infrared thermal imaging on newborn infants for mapping skin temperature, we were expecting to detect very small temperature changes in the nostrils region comparing to the magnitude in adults [20, 23, 26]. Therefore, we expected difficulties to detect the respiration thermal signature in infants, and were supposed to find this temperature difference between inspiration and expiration phase in the range between 0.3C to 0.7C. The physics of this phenomenon are based on the radiative and convective heat transfer component during the breathing cycle (see Figure 5). In fact, including all these influences in one model is a complex task, but should include the simulation of the airflow pathway, temperature gradient distribution throughout the nasal cavity, and the blood perfusion in the nasal cavity and nostril regions [18, 25]. Hence, the mathematical approximation for the IRTR signature depends on the five main parameters shown in Figure 6, and the total heat flow rate ( Q R R ( t ) ) contributing to the thermal signature of one respiration cycle can be expressed as follows:
PIR sensor is the short form of passive Infrared sensor. The main ideology is to provide security. This is based on PIR sensor with an IC that produces siren or buzzer sound. The PIR sensor detects the IR radiation which is emitted from the humans and then it produces a digital output. Mostly it is used in motion detectors, security alarms, and automatic lighting applications. In general they detect movement i.e. changes the amount of infrared radiation. In turn this digital output is given to the Arduino Uno. after getting digital signal from the PIR sensor, the Arduino UNO then triggers the UM3561 siren. Thus it produces the sound when only human is detected. The UM3561 is a ROM IC. It is used to generate ambulance siren, machine gun sound, fire engine siren, police sounds etc.
Thus the temperature will be different from a moving human and a wall present there which is constant. Thus the word passive in Passive Infrared Sensor explains clearly that it does not emit a radiation rather than it accepts the incoming infrared radiation.
Examples of over-roadway sensors include video image processors, which use cameras mounted on tall poles adjacent to the roadway or on traffic signal mast arms over the road; microwave radar, laser radar, ultrasonic, and passive infrared sensors installed either alongside or above the road; and acoustic sensors installed alongside the road. The required mounting configuration is a function of the intended application. Modern over-roadway sensors provide a viable alternative to inductive-loop detectors.
Sensor technology and operating theory indicate that the principal in-roadway sensors (inductive-loop, presence-detecting magnetometers, and passage-detecting magnetic detectors) are suitable for some applications but unsuitable for others. For example, magnetic detectors generally cannot be used for vehicle presence detection. 2ff7e9595c
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