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Active infrared and passive infrared alarm features, differences and application

  • Author:Snoppy Huang
  • Source:CPS Encyclopedia
  • Release on :2016-07-25
Active infrared and passive infrared alarm features, differences and application 
   Works for the infrared emission of infrared emission tube infrared beam emitted by smoke, dust particle scattering, of course, is proportional to the concentration of the scattered light intensity and smoke, so the strength of the received photodiode infrared beam will occur changes, into a signal point, is converted to the final alarm signal. Alarm for smoke detectors is performed by the optical maze, maze, there is a set of infrared transmitter and receiver photocell beam angle of 135 degrees. When the smoke-free environment, the reception can not receive infrared emission tube infrared light emitted by the subsequent sampling circuit without electrical signal change; environment when there is smoke, smoke particles enter the maze so that infrared emission emitted from scattered light, the intensity of the scattered infrared light and smoke have a linear relationship between the concentration of the follow-up sampling circuit is changed, the alarm built-in main chip Analyzing these changes amount to confirm whether fire, once confirmed fire alarm sends out alarm signals, fire indication lamp (red) lights up, and start the buzzer alarm.
   
Infrared alarm system is divided into active and passive infrared alarm infrared alarm, let's introduce the alarm difference between the two and their respective characteristics.

   Active infrared intrusion detector is composed by a transmitter and a receiver, the transmitter is power, light source and an optical system consisting of a receiver by the optical system, photoelectric sensors, amplifiers, signal processors and other components.

   Active Infrared Detector is an infrared beam shutter-type alarm transmitter in infrared light-emitting diodes in the power of the excitation, emits a modulated infrared beam (the wavelength of the light beam between about 0.8 to 0.95 microns) after the role of the optical system into parallel light emitted. This beam is received by the receiver, the receiver of infrared photoelectric sensor to convert an optical signal into a signal processing circuit after the alarm control. By the transmitter emits an infrared region through the prevention arrive at the receiver constitute a cordon. Under normal circumstances, the receiver receives a stable optical signal when someone invaded the cordon, the infrared beam is blocked, the infrared signal received by the receiver changes, extraction of this change, amplified, and appropriate treatment, the controller alarm signal sent. Currently there are two such probe beam, as well as three-beam multi-beam infrared fences. General application in the perimeter to prevent the majority, the biggest advantage is to prevent distance, can reach more than ten times the passive infrared detection range.

Active Infrared Detector:
    Using active infrared way to achieve security alarm detectors. Active infrared detector consists of an infrared transmitter, an infrared receiver and alarm controller. Were placed in income, the originator of the optical system is generally used in an optical lens serves to focus the infrared light beam into a parallel beam smaller role in the energy infrared light to focus on delivery. Infrared light is invisible to the human eye spectral range, it was through this invisible cordon, blocking all or part of the inevitable infrared beam. The strength of the receiver output electrical signal will therefore produce changes, which initiates alarm controller alarm.


Passive infrared detectors:
    PIR (Passive infrared detectors) passive infrared mode, has reached the security alarm detectors. Part of the passive infrared detector consists of an optical system, pyroelectric sensor (or infrared sensor) and alarm controller. Detector itself does not emit any energy but only passively receive, detect infrared radiation from the environment. Once human infrared radiation coming through the optical system focus on making Pyroelectric mutate electrical signal, and an alarm. Passive infrared detector infrared energy is mainly based on changes in the outside world to determine whether someone is moving. There are the body's infrared energy and environmental differences when people through the detection area, the detector collected from different locations of this infrared energy changes, and then by analyzing the alarm.
    Passive infrared alarm detecting human radiation as the goal, so the pyroelectric element to a wavelength of about 10μm infrared radiation must be very sensitive.
    For only sensitive to infrared radiation the human body, in its radiation face to face is usually covered with a special Fresnel filter, interference by the environment obviously control.
    The sensor consists of two pyroelectric elements in series or in parallel to each other. And two electrodes made from the opposite direction, ambient background radiation on the two pyroelectric elements have almost the same effect, to produce pyroelectric effects offset each other, so no alarm signal output.
    Once people invaded detection area, part of the infrared radiation through the focusing mirror, the pyroelectric element was received, but different two pyroelectric element receives heat, pyroelectric is different not offset, the signal processing and alarm.
    However, the external environment is: not only the human body emits infrared energy, many objects under certain conditions will emit infrared energy, and this energy in visible light, especially prominent, so anti-white light interference of any passive infrared detector has become an important index. Stable at room light, infrared energy relatively constant, this detection method performs very well. But the situation is different outdoor long infrared passive infrared detection outdoors only a few manufacturers can do. The so-called indoor and outdoor a small step, three-step technological content.
Active Infrared Detector Device Selection

    1. According to the site to prevent the minimum, maximum temperature and duration, select the appropriate operating temperature with active infrared intrusion detectors; if the ambient temperature is too low, you can use special heater to ensure the normal operation of the detector.
    2. Active infrared intrusion detectors fog severely affected, should select the device with automatic gain function (such equipment when climate change will automatically adjust the sensitivity) outdoor use; In addition, the detection range of the actual alert distance for the selected device aside 20 % or more of the balance, in order to reduce false alarms caused by climate change system.
    3. Be sure to use outdoor use dual beam or 3-beam active infrared intrusion detectors to reduce the birds, leaves and other false alarms caused by the system.
    4. Active infrared intrusion detectors used in the near infrared wavelength light-emitting diodes, respectively 0.85μm and 0.95μm. The former red exposure phenomenon, its good concealment than the latter.
    5. Foggy area, a large outdoor environment dirty sand area should not use active infrared intrusion detector.
    6. When open area or in the wall, use active infrared intrusion detector on the roof, should be selected with lightning protection devices.
    7. In case of off the wall, and the distance and near, the reflection device can be used to reduce the number of detectors to use.
    8. Outdoor active infrared intrusion detectors use the maximum beam distance should be more than six times as specified by the manufacturer of the detection distance.