Useful Information
- ♦ Application
- ♦ Cameras
- ♦ Lenses
- ♦ Light & CCTV
- ♦ Number Plate Recognition
- ♦ Thermal Imaging
- ♦ Housings
- ♦ Digital Images
- ♦ Digital Technology & Recording
- ♦ Video Compression
- ♦ Infrared
- ♦ IR & LED Lighting
- ♦ IP CCTV & Technology
- ♦ Monitors
- ♦ Motion Detection
- ♦ Multiplexers
- ♦ PIR Movement Sensor
- ♦ Remote Positioning Devices
- ♦ Video Motion Detection
- ♦ Multiple Screen Display
- ♦ Signal Noise Ratio
- ♦ Survellance Vechicle
- ♦ Three-dimensional (3D) design in CCTV & Security
- ♦ Transmission of Video Signals by Cable
- ♦ Transmission of Video Signals by Remote Methods
- ♦ Transmission of Video Signals by Fibre Optics
- ♦ Video Analysis
- ♦ Wireless CCTV
Passive Infra Red Movement Sensor
All Remote Monitored or Event Driven CCTV systems require a reliable means of detecting a person or persons entering into the protected area.
There are many different types of sensors from video motion analytics to microwave Doppler detectors but by far the most reliable and cost effective way is to use a PIR detector.
These detectors are very common in internal burglar alarm systems where they operate in controlled environments. Design considerations are different for external PIR's because they have to operate reliably in an uncontrolled environment. These detectors are subject to rain, high humidity and large temperature changes from sub zero to tropical climates. They have to cope with strong winds which cause trees and foliage to move about in the field of view. Visible light from car headlights will flash across their lenses on dark nights. Pets and wild animals will roam around in the field of view.
Modern powerful micro controllers are now very affordable for the PIR detector market and allow the designer to implement a high degree of digital filtering to counter these changing conditions.
This filtering can be adjusted by the user and is normally described as Pulse Counting. Original analogue detectors simply counted the pulses from the comparator outputs but modern detectors apply different algorithms to filter the digitised infrared signal. It is common to still call this filtering, Pulse Counting but it is not the same.
Despite the degree of sophistication and filtering in these detectors it is still prudent to consider carefully the positioning of the detector. Correct positioning will reduce the need to set a high level of filtering and therefore the detector will be more sensitive to intruders. Detectors should always be mounted facing into the site to avoid detecting outside the protected area. This is in fact a requirement in the BS8418 British Standard for Remote Monitored Systems. Detectors should be mounted at the correct height as specified by the manufacturer as this will affect the detection pattern. Many external detectors are designed to be mounted at no more than 2.5 metres to comply with health and safety requirements. Some detectors are designed to be mounted at greater heights but this will then require the use of a cherry picker.