PIR Detection Technology and Reliability
June 2011
PIR detection technology and reliability
Passive Infra Reds (PIRs) are the most cost effective, early detection tools for intruder alarm and event-driven CCTV systems. They use Infra Red body heat emissions to detect movement and raise an alarm. The alarm can range from a siren or lighting on site, to an alert to a remote CCTV monitoring station for an operator response.
Unfortunately, some PIRs can be inaccurate and incorrectly detect harmless objects, leading to false alarms. Classic false triggers include animals, lighting changes, sunlight reflections, foliage, litter, insects and birds.
We asked Graham Creek, MD of Luminite, the UKs leading PIR manufacturer and designer of the wireless and hard-wired Genesis PIR detector systems, to explain how advanced technology within PIRs and installation good practice can play a significant role in reducing PIR false alarms.
Common false alarm causes
The most common cause of PIR false alarms is “detection overspill”, where the PIR detects passers-by or distant traffic beyond the perimeter of the building or grounds it is protecting. Further triggers are loose materials, such as polyethylene sheeting, plastic bags and tarpaulins flapping in the wind, swaying foliage and moving animals. Bright light, such as sun reflections off puddles or windows are also common triggers.
Despite this somewhat comprehensive list of false alarm triggers, there is much that can be done to reduce them.
Choose the correct lens pattern
Most PIRs have a choice of lens detection patterns. Installers can select short range or long range detection zones. Similarly, vertical and horizontal “curtains” can be activated if an intruder crosses a specific line. Selecting the correct PIR lens pattern for each application is vital. Using settings for object size and careful positioning of the PIRs can also help to rule out some false activations caused by overspill and animals.
Use technologies to combat lighting changes
Dual or quad sensing is a technique within PIRs that can reduce some false alarms. Many PIRs use only one pyro detection sensor. If this detects IR changes an alarm is given. When two pyro sensors (dual or quad technology) are used within one PIR and angled slightly apart, activation can only occur when both sensors are triggered simultaneously, reducing false alarms.
Black mirrors reduce white light issues. Instead of using normal mirrors within the PIR to reflect IR light back into the sensor, black mirrors are used to prevent white light from flooding the sensor and causing false alarms. Black mirrors do not compromise detection efficiency and effectiveness.
Use wireless PIRs, with their added installation benefits
The IR detection technology and the radio-technology, used for wireless network communication within PIRs, both have low power consumptions. This means a wireless, PIR detector’s battery life can be well over two years. No wiring is required when installing the PIRs. This reduces installation time, makes the PIR network more reliable and dramatically reduces the errors and aggravation caused by cabling multiple PIRs back to a DVR.
Wireless PIRs have some important additional benefits. They can be positioned for optimal detection performance and system effectiveness, as they do not need to be placed near network or power cables. Our Genesis wireless PIR range will transmit up to 1km, so the PIRs can be positioned on a site’s perimeter looking into the site, not outwards. This eliminates overspill issues and with astute PIR positioning, can reduce foliage and ambient light issues too. In my opinion, wireless PIRs enable installers to take a more creative approach to PIR system design and positioning, allowing false alarm reduction to be designed into the system from the outset.
Use wireless, network technology improvements
There are constant improvements being made in PIR and wireless network technology. They are worth using because they are designed to reduce false alarms. Here is just one example I have been developing. The industry standard for wireless networks is Simplex Radio. Our Genesis system uses Simplex for wireless network communications between up to 64 PIRs and a transceiver (Masthead). The PIR pings the transceiver every minute to check network strength, raising an alarm after 15 minutes if this process stops. We will be launching a duplex mesh radio system imminently, where the network is not only created between the PIR and transceiver, but also between all the PIRs in a network allowing a signal to take the most reliable path. An added bonus is that duplex radio also allows PIR updates and settings to be uploaded remotely.
Utilize system testing
One of the most effective ways of reducing false alarms is by testing the PIR detection extents and the wireless network system strength on site, before a system goes live. We have introduced a Walk Test Instrument for this exact purpose. It will sense the extents of the detection area, verify signal wireless strength, display the lens pattern in each detector and even communicate battery life. If an installer is unable to effectively test the PIR system they are fitting, they are working blind and errors will occur, increasingly false alarms.
There is much that can be done to reduce false alarms from PIRs. I believe they are an invaluable detection tool that can significantly improve site security. They are inexpensive, easy to install and the technology they use ensures their excellent green credentials.
Luminite designs and manufactures the wireless and hard-wired Genesis PIR detection systems, built and supported in the UK.
For more information on the Genesis PIR detection range or for training on PIR installation good practice, contact Luminite on 020 8368 7887 or by email.
