The upper end of this series is connected with the gate of an in-built FET which acts as a small IR signal amplifier. On the left we can see a pair of IR sensing elements connected in series. The following figure shows the internal layout or the configuration inside a standard PIR sensor. The following rough Gif simulation shows how a PIR sensor responds to a moving human and develops a couple of short sharp pulses across its output leads for the required processing or triggering an appropriately configured relay stage Internal Layout of a PIR When a human being or a relevant IR source moves past a PIR sensor, the radiation cuts into the pair of sensing elements in an alternate manner, triggering the output to generate a pair of ON/OFF or high and low pulses, as depicted in the following waveform: This two-step sensing process improves the overall stability of the sensor and helps to detect IR signals only from human presence. These sensors employ a dual or a pair of sensing elements for sensing the IR signals in two steps, which ensures a foolproof detection by cancelling the unwanted temperature variations within the existing EMI stage. The sensing operation of a pyroelectric infrared sensor is based on the property or characteristic which becomes responsible for altering the polarization of its material in response to temperature changes. If one of the sensitive crystals detects change in infrared (increment or decrement) than the other sensitive crystal, the output gets triggered.Ī dome shaped plastic structure is normally placed over this sensitive crystal which acts as lens to focus the infrared light on the sensors. It actually houses two pyroelectic sensors for detecting moving objects. The dark portion of the metal where the IR sensitive crystal is housed, the sensitive crystal can detect the level of infrared in the surroundings.
The PIR sensor module can be divided in to two parts an infrared sensitive crystal and the processing circuit. It can detect any infrared emitting object such as human beings or animals if it is the range of the sensor, or moves away from the range, or moves within the range of the sensor. PIR is an electronic sensor which detects the changes in the infrared light across certain distance and gives out an electrical signal at its output in response to a detected IR signal. PIR stands for Pyroelectic Infrared Radial Sensor or Passive Infrared Sensor. Typical PIR Module Internal Circuit Diagram.
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