PIR detectors explained

October 2005 Perimeter Security, Alarms & Intruder Detection

Elvey Security Technologies is a proud distributor of the high performance intruder detectors from Optex. Optex products are most reliable, easy to install and affordable. All Optex detectors are 100% tested before being introduced to the market and with continuous R&D, Optex is constantly improving its existing detectors to meet the needs of the security market.

Elvey Security Technologies, together with Optex, would like to add some insight to the mechanisms behind the Optex detectors.

How do PIR detectors work?

Passive infrared (PIR) detection is achieved by monitoring changes of the far infrared levels in the sensors field of view. All objects emit infrared radiation at or around a wavelength of 10 µm. The sensor activates when a human being moves against a background that is emitting more or less radiation. Effective detectors are able to discriminate between humans and other sources of infrared.

Conventional models
Conventional models

Unique technologies

Using a number of unique technologies, many of which are patented, Optex detectors are able to discriminate between human and other sources of infrared such as moving curtains or blinds, radiators, office equipment, pets, sunlight and reflections. The aim of all the technologies is to reduce the incidence of a false alarm.

Double conductive shielding

Double filtering and conductive metal shielding cover the pyroelectric sensor, blocking and grounding out visible light and radio frequency interference (RFI). Only infrared energy passes through the filter, minimising false alarms from direct or reflected sunlight and car headlights.

Quad zone logic

These create an extremely high vertical zone density; two or three times the size of that in conventional PIRs. These taller zones capture the entire body mass of a person and enable detection of the smallest temperature contrast between them and the background. In addition, the vertical detection density takes into account dead zones created by furniture or partitions.

Quad zone logic
Quad zone logic

Multifocus technology

Multifocus technology creates zones with high vertical density, optimising detection sensitivity and enabling detection to remain stable even in high temperature conditions.

Temperature compensation

Temperature compensation increases detection capability in high temperature conditions, where the background temperature is similar to that of the human body. It maintains a high level of false alarm protection and helps prevent valid alarms being missed by automatically adjusting sensitivity according to the environmental temperature.

Spherical lens design

Traditional PIR detectors use a flat lens bent into a curve to focus infrared energy onto the pyroelectric sensor. This is not the most accurate method, because the distance between the lens and the pyroelectric sensor (the focal length) varies for each detection zone, creating distortion. The Optex spherical lens design eliminates distortion by providing a uniform focal length for every detection zone. Additionally, the sphere is one of the strongest geometrical structures, making spherical lenses superior both optically and mechanically.

Conventional structure
Conventional structure

Sealed optics

With conventional PIR detectors, small inserts and draughts can cause false alarms by getting between the lens and the pyroelectric sensor. This is prevented by 'sealed optics', which make this space separate sealed optical compartment ensuring that it remains empty and undisturbed at all times.

Sealed optics
Sealed optics

For more information contact Elvey Security Technologies, 011 401 6700, sales@elvey.co.za, www.elvey.co.za


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