A pyroelectric infrared sensor must be used together with a Fresnel lens or other light collecting component.
Because the total energy of the infrared rays emitted from a human body is extremely low and the energy density decreases in inverse proportion to the square of the distance, the energy which enters the sensor is exceptionally small.
Accordingly, optical amplification in the form of a Fresnel lens is required for reliable sensor operation in each set.
If an optical system is not used in front of the sensor, the sensor directivity will change as shown in the figure below, and the detection area will not be formed.
Therefore, an optical system is used to focus the infrared rays onto the element. The detection area is designed according to the optical system.
As shown in the figure below, a Fresnel lens is designed so that the rays pass through the same point (focal point).
Because the detection output differs according to the electrode placement, be sure to pay attention to the sensor polarity.
For dual type sensors
Dual type sensors have a structure which places two electrodes in series connected with reverse polarity.
(1) Because it is sensitive to input which sequentially crosses (horizontal) the two electrodes, this type is suited to use in wall-mounted sets (human body detection from movement in the horizontal direction). (As a result, erroneous signals due to temperature changes in the surrounding environment are reduced)
(2) In principle, this type does not have any sensitivity in the direction of simultaneous input to both electrodes (vertical or motion from the front). Infrared rays (movement) which are simultaneously input to both electrodes generate signals with different polarities from the two electrodes at the same time, which cancel each other out, and as a result the sensor signal is not generated.
Because the detection output differs according to the electrode placement, be sure to pay attention to the sensor polarity.
For dual type sensors
Dual type sensors have a structure which places two electrodes in series connected with reverse polarity.
(1) Because it is sensitive to input which sequentially crosses (horizontal) the two electrodes, this type is suited to use in wall-mounted sets (human body detection from movement in the horizontal direction). (As a result, erroneous signals due to temperature changes in the surrounding environment are reduced)
(2) In principle, this type does not have any sensitivity in the direction of simultaneous input to both electrodes (vertical or motion from the front). Infrared rays (movement) which are simultaneously input to both electrodes generate signals with different polarities from the two electrodes at the same time, which cancel each other out, and as a result the sensor signal is not generated.
Quad
The quad type sensor is 2 dual type sensors put into 1 package.
The output of 2 dual type sensors in 1 sensor.
Unlike the dual type, the quad type also has vertical sensitivity, making it suitable for use on sets mounted to ceilings.
Compared to the dual type, more detection areas can be set, allowing for slight movements to be detected more easily. (As compared to the dual type)
*Achieved by combining sensors with optical design.