Passive Infrared sensor (PIR) motion detector

when you walk into an automatic door, did you think : how could the door opens automatically when someone is approaching?
If you think about a motion sensor, so your answer is true.

usually, the automatic doors installed a passive infrared.
Passive infrared is a motion sensor which have very wide application, not only on the automatic doors, but also in another application. So, lets check this post to learn more bout it…

Design

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 an approximately 1/4 inch square of natural or artificial pyroelectric materials, usually in the form of a thin film, out of gallium nitride (GaN), caesium nitrate (CsNO₃), polyvinyl fluorides, derivatives of phenylpyrazine, and cobalt phthalocyanine. (See pyroelectric crystals.) Lithium tantalate (LiTaO₃) is a crystal exhibiting both piezoelectric and pyroelectric properties.

The sensor is often manufactured as part of an integrated circuit and may consist of one (1), two (2) or four (4) ‘pixels’ of equal areas of the pyroelectric material. Pairs of the sensor pixels may be wired as opposite inputs to a differential amplifier. In such a configuration, the PIR measurements cancel each other so that the average temperature of the field of view is removed from the electrical signal; an increase of IR energy across the entire sensor is self-cancelling and will not trigger the device. This allows the device to resist false indications of change in the event of being exposed to flashes of light or field-wide illumination. (Continuous bright light could still saturate the sensor materials and render the sensor unable to register further information.) At the same time, this differential arrangement minimizes common-mode interference, allowing the device to resist triggering due to nearby electric fields. However, a differential pair of sensors cannot measure temperature in that configuration and therefore this configuration is specialized for motion detectors, see below.

ceiling-mount-passive-infrared-motion-detector-397090

Passive infrared (PIR) sensors detect infrared energy radiating from objects within their field of vision.

Unlike infrared optical sensors that use an LED transmitter and IR receiver, the PIR emits nothing. As its “passive” name suggests, it responds only to infrared energy radiated by the object being sensed. The most common object a PIR sensor detects is the human body, so these sensors find use in automatic light switches, alarm systems, and door openers.

passive infrared block diagram

PIR-based motion detector

In a PIR-based motion detector (usually called a PID, for Passive Infrared Detector), the PIR sensor is typically mounted on a printed circuit board containing the necessary electronics required to interpret the signals from the pyroelectric sensor chip. The complete assembly is contained within a housing mounted in a location where the sensor can view the area to be monitored. Infrared energy is able to reach the pyroelectric sensor through the window because the plastic used is transparent to infrared radiation (but only translucent to visible light). This plastic sheet also prevents the intrusion of dust and/or insects from obscuring the sensor’s field of view, and in the case of insects, from generating false alarms.

A few mechanisms have been used to focus the distant infrared energy onto the sensor surface. The window may have multiple Fresnel lenses molded into it.

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