Hi All,

I have a query related to the logic behind PIR integration in lighting systems so that they form a non-serviceable components.

Are there any functional requirements or benefits by having a PIR lens so that it is nonreplaceable component (reduction in system’s use, safety, etc) or are they designed in that way so as to force consumers to replace entire units once the PIR lens requires replacement?

Thanks in advance.

 

Lenses there form the long queue of bright points moving across the sensor when You move in the room. Normal lense gives one shape instead of multiple points. They cannot be used.

 

Are there any functional requirements or benefits by having a PIR lens so that it is nonreplaceable component

A fresnel lense significantly reduces the necessary size of a lense. That is, if the lense were NOT a fresnel lense, the size and focal point of that lense would be impractical to use in a sensor. A fresnel lense allows for a much greater coverage area in a small space. It uses a series of concentric annular sections to make up the lense. It is also used in theatrical lighting to cover/fill large areas with light.

 

Fresnel lense may not be used there because it forms the one single picture of object. In case of PIR there must be hundred point-shaped pictures of single object in the same time.

 

Fresnel lense may not be used there because it forms the one single picture of object. In case of PIR there must be hundred point-shaped pictures of single object in the same time.

Why do you think there must be 100 point-shaped pictures of a single object?

That’s incorrect.

Passive infrared (PIR) sensors only detect infrared radiation. Passive infrared sensors are comprised of:

• Two strips of pyroelectric material (a pyroelectric sensor)
• An infrared filter (that blocks out all other wavelengths of light)
• A fresnel lens (which collects light from many angles into a single point)
• A housing unit (to protect the sensor from other environmental variables, such as humidity)

 

Hi,
A typical domed PIR Fresnel lens module will only detect movement of an animal's radiated body IR.
As the animal moves at right angles to the detection plane of the sensor, the lens creates in effect a very low frequency signal due to the varying intensity of the IR falling on the sensor, due to the lens pattern.

This low frequency is amplified, the fixed level of background IR, effectively DC, is blocked.

E

Added PDF.

 

RE:""
Why do you think there must be 100 point-shaped pictures of a single object? That’s incorrect.""
I have by own hands repaired and distracted hundreds and hundreds of different shop-bought PIR constructions. Probably You are right about wider sortment of it, but not in the 3 USD sample on the store shelf, where those others are wildest exotics. Those small cubicles on the plexiglass lense is each the separate micro-lense forming a separate point-like picture. When the intruder moves, the plethora of points makes plethora of pulses instead of one single pulse of alarm. Those series are integrated and then the real alarm is triggered.