Lens choice is important when installing PIR sensors.

Aside from pyroelectric sensor quality, is there a feature or function of PIRs that’s more important than others?

A: Arguably the most important aspect of a quality PIR is selection of optics. A badly designed lens will lack resolution, will display reduced sensitivity and will have dead zones from which directions the sensor can be approached without activating an alarm. Some sensors will be supplied with a choice of lens and others will endeavour through their design to offer of both broad coverage and long-range patterns.

While getting a quality lens is important, choosing the right lens type for your applications is key. There are 6 primary lens patterns – and these can be applied generally to both fresnel lens types and mirror optics:

* Long range, dual zone, narrow coverage lenses are used to monitor narrow corridors with crossing points to protect long rows or windows

* Long range, multizone, narrow coverage lenses are designed for use with long corridors without crossings in which intruders will move towards or away from the sensor

* Multizone curtain lenses are mounted on ceilings above entrance doors or in glazed areas. They’re a detection fence from floor to ceiling and any intrusion through them will generate an alarm

* Broad multizone, wide angle or volumetric: These lens types are the most common found. They are more sensitive to movement across a protected space at right angles to their radial zones. They’re ideal for smaller spaces in domestic homes and small offices

* Ceiling mount PIRs have two-zone, 360-degree coverage, with conical zone arrangement arrayed in two circumference lengths. These sensors are ideal for use in offices that have large numbers of partitions between waist and shoulder height. Multiple installations generally employ overlapping pools of detection.

We like mirror optic lenses in tough environments. Having spent time fooling around with some mirror optic PIRs, SEN came away impressed with their effectiveness at long range. Mirrors do mean greater expense, so there’s a decision to be made with lens choice.

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