PIR Fresnal Lense?????

Rooter

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I am using the RS PIR.  The lense I believe is called a "fresnal" lense or something like that.  When I mount my unit is it necesary to keep the lense on or can I just mount it and have it work throught a regular piece of lexan.  How will this affect my range and area of detection?
 



sven

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You do need the fresnal lense.  If you look closely at it you will notice it has some patterns cut on it.  This is what reflects the infrared energy to the pir on the board.  I basically works the opposite of a car headlight assembly.  The headlight lense has different patterns cut in it to shine the light from the bulb in different directions.

Do a search on the board for "fresnal" and you will find a lot of info on placement.  The distance between the lanse and the sensor is important.
 

shrtcirkt

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Rooter,
Like Sven said, you do need the Fresnel (pronounced Frennel) lens. But you also need to be aware that the lenses have a focal distance. That is to say that the distance from the PIR to the inside surface of the lens is critical. So if you remount the lens be sure it is the proper distance from the sensor.
 

Archilochus

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Hi Rooter,
When searching the forum or 'net - also try the spelling "Fresnel" - it tends to get spelled both ways.  For technical info and history of the Fresnel lens, check http://www.fresneltech.com

Archilochus
 


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