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Introduction
A motion detector is an electronic device that detects the physical movement in a given area and transforms motion into an electric signal. The motion detector may be electrically connected to devices such as security, lighting, audio alarms, and the like. Motion sensors are used in a wide variety of applications and as a result many different types of motion sensors are available. Motion detectors are mainly used in for security systems. For example, motion detectors are typically positioned near exterior doorways or windows of a building for monitoring the area around the building. Upon detecting motion, they generate an electrical signal that is transmitted to a preselected audible alarm or lighting device which is then activated. A number of different technologies are used for motion detection. Motion detectors typically employ ultrasound, passive infrared (PIR), or radar detection techniques. Among the most used and most effective type of intrusion detection devices are the passive IR detectors which in recent years have replaced other types such as microwave or ultrasonic detectors.
TYPES OF SENSORS
Microwave sensors
Microwave sensors are used in large apartments since microwaves can penetrate through dielectric mediums. But they are generally not used because the unit consists of expensive super-high frequecy component whose radiations are not healthy for living organism
Infrared sensors
Infrared (IR) detectors are widely known in the arts of intrusion detection and in fire/smoke detection. These detectors have basically two forms: active and passive.
ACTIVE SENSORS
Active IR detectors include a radiation source and an IR sensor which is sensitive to interruptions in the radiation sensed from the source. These detectors are used as intrusion detectors by providing a path of radiation from the source to the sensor in a place where the path is likely to be interrupted by an intruder.
PASSIVE SENSORS
A passive infrared motion detection system detects heat energy radiated or emitted by an object, such as a body of a person, moving across a field of view of a heat sensor, such as a pyroelectric detector, of the motion detection system. Passive infrared motion detectors generally use an optical collection system and multiple sensing elements of alternating polarity to create a detection pattern in the volume of interest. Passive IR detectors generally employ a group of radiation sensors coupled through amplifiers to a logic circuit. PIR motion detectors are perhaps the most frequently used home security device.
Passive IR motion detectors are usually designed to provide an indication to an alarm panel in response to detecting IR that is indicative of motion of the object. The alarm panel is responsive to receipt of the breach indication to cause an alarm condition to occur. Infrared motion detector devices are often used in automatic light switches and security systems to turn on aA motion detector is an electronic device that detects the physical movement in a given area and transforms motion into an electric signal. The motion detector may be electrically connected to devices such as security, lighting, audio alarms, and the like. Motion sensors are used in a wide variety of applications and as a result many different types of motion sensors are available. Motion detectors are mainly used in for security systems. For example, motion detectors are typically positioned near exterior doorways or windows of a building for monitoring the area around the building. Upon detecting motion, they generate an electrical signal that is transmitted to a preselected audible alarm or lighting device which is then activated. A number of different technologies are used for motion detection. Motion detectors typically employ ultrasound, passive infrared (PIR), or radar detection techniques. Among the most used and most effective type of intrusion detection devices are the passive IR detectors which in recent years have replaced other types such as microwave or ultrasonic detectors.
Infrared (IR) detectors are widely known in the arts of intrusion detection and in fire/smoke detection. These detectors have basically two forms: active and passive.
Doppler shift motion detectors are active motion detectors in which a wave transmitter transmits waves into a monitoring area, and then a wave receiver receives the reflected waves and produces a reception signal. By detecting the Doppler shift in the reflected signal, the detector circuitry detects whether a moving object is present in the area. Typical applications include intruder alarms and automatic door openers, for which a unit of conventional construction comprises a gunn diode oscillator mounted in a cavity resonator such as a simple waveguide tube. However, Doppler radar-based motion detectors are disadvantageous because of limited materials penetration, microphonics, frequency crowding, and poor short-range operation.
Ultrasonic Movement Detector
Ultrasonic motion detectors project and receive ultrasonic sound energy in a region of interest. Object motion within the region of interest and in the range of the ultrasonic motion sensor is detected and an alarm signal representative thereof is produced. The effective range of ultrasonic motion detectors differs from design range whenever the actual ambient atmospheric sound propogation conditions vary from the design or nominal atmospheric conditions. Ultrasonic motion detectors are commonly used for automatic door openers and security alarms.
Ultrasonic motion sensors work on the principle of Doppler effect similar to radar or sonar.
DOPPLER EFFECT: It states that there will be an apparent change in frequency of signal with time when source and observer are in relative motion with respect to eachother
Ultrasonic sensor generates high frequency sound waves and evaluates the echo which is received back. Ultrasonic motion sensors are characterized by small power consumption,low cost,high sensitivity.These are commonly employed in office and home security.
TYPES OF ULTRASONIC SENSORS
Active sensors:Active sensors emit sound waves from the transducers and when there is any movement detected the sound waves get disturbed and activate any electrical or electronic control unit connected through relay.
Passive sensorsassive sensors operates on the principle of sounds such as breaking of glass or striking of metal.
These sounds produce waves which is detected by the sensor.These sensors offer very high sensitivity.