In the field of electronic anti-theft and human body detectors, passive pyroelectric infrared detectors are widely used. They are popular with users and professionals for their low price and stable technical performance.
Working principle and characteristics of passive pyroelectric infrared probe:
The human body has a constant body temperature, generally at 37 degrees, so it emits infrared rays with a specific wavelength of about 10UM. Passive infrared probes work by detecting about 10UM of infrared rays emitted by the human body. About 10UM of infrared light emitted by the human body is enhanced by a Firth filter and focused on an infrared sensing source. Infrared induction sources usually use pyroelectric components. Such components lose their charge balance when they receive changes in the temperature of the human body’s infrared radiation, releasing their charges outward, and subsequent circuits can generate alarm signals after detection and processing.
1) This probe is aimed at detecting human radiation. Therefore, pyroelectric elements must be very sensitive to infrared radiation with a wavelength of about 10UM.
2) In order to be only sensitive to the infrared radiation of the human body, its radiation exposure surface is usually covered with a special Filth filter, so that the environmental interference is obviously controlled.
3) A passive infrared probe whose sensor contains two pyroelectric cells connected in series or parallel to each other. In addition, the two polarization directions are exactly opposite, and the environmental background radiation has almost the same effect on the two pyroelectric elements, so that the electric discharge effects cancel each other out, so the detector has no signal output.
4) Once a person intrudes into the detection area, the human body’s infrared radiation is focused by a part of the mirror and is received by the pyroelectric element, but the two pieces of pyroelectric element receive different heat, and the pyroelectric element is also different and cannot be offset. After signal processing And the alarm.
5) The filth filter has different focal lengths (induction distances) according to different performance requirements, which results in different monitoring fields of view. The more the field of view, the tighter the control.
Advantages and disadvantages of passive pyroelectric infrared probes:
It does not emit any type of radiation itself, and the device consumes very little power and has good concealment. Low price.
Easy to be interfered by various heat sources and light sources;
The passive infrared penetrating power is poor, and the infrared radiation of the human body is easily blocked and not easily received by the probe;
Susceptible to interference from radio frequency radiation;
When the ambient temperature is close to the temperature of the human body, the detection and sensitivity are significantly reduced, sometimes causing short-term failure.
Installation requirements for infrared pyroelectric sensors: Infrared pyroelectric human sensors can only be installed indoors, and the false alarm rate has a great relationship with the location and method of installation.
Proper installation should meet the following conditions:
1. The infrared pyroelectric sensor should be 2.0-2.2 meters above the ground.
2. The infrared pyroelectric sensor should be kept away from places sensitive to air temperature changes such as air conditioners, refrigerators and stoves.
3. No screen, furniture, large bonsai or other spacers are allowed within the detection range of the infrared pyroelectric sensor.
4. Do not point the infrared pyroelectric sensor directly to the window, otherwise the disturbance of the hot air flow outside the window and people walking will cause false alarms, and conditionally pull the curtain up. Do not install the infrared pyroelectric sensor in places with strong airflow.
The sensitivity of infrared pyroelectric sensors to the human body is also strongly related to the direction of human movement. The infrared pyroelectric sensor is not sensitive to the radial movement response, but sensitive to the transverse direction (that is, the direction perpendicular to the radius) movement. Choosing the right installation location on the site is an extremely important part of avoiding false alarms by the infrared probe and obtaining the best detection sensitivity.
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