Advantages And Disadvantages Of PIRs

♦ Advantages And Disadvantages Of PIRs – Some of the advantages of PIRS include low false alarm rates when compared to microwave and ultrasonic sensors, miniscule power drains, no energy emissions, no moving parts and simple electronics.

PIRs have a longer detection range than ultrasonics, are cheaper than most other technologies, will not interfere with each other when installed in groups and can be adjusted in terms of lens pattern and sensitivity while in the field.

There are disadvantages with PIR technology, too. For a start, increases in ambient temperature will affect a PIR’s range and sensitivity. And it’s possible for intruders to wear a suit or carry a shield that reflects body heat to block pyroelectric sensing. You can use discreetly located sensors on the same zone loop or randomly placed internal reed switches on self-closing doors to beat this sort of attack.

Another weakness is that there’s not the density or uniformity of coverage with PIRs that you get with some other technologies. There can be dead zones and it’s possible for furniture or pallets of stock to block the sensor’s view. Nor will the PIR alarm if the sensing element fails, something that beam sensors will do. Generally, the PIR sensor’s detection range is limited to 15m x 15m x 50m in wide angle and 50m in narrow beam, or a circular 15m pattern, though there are specialist sensors that do better.

Another negative is the fact random IRE signals will cause false alarms and there’s a maintenance requirement. In dry, dusty environments, particles will be electrostatically drawn to the device where they’ll stick and cloud its vision. Lenses and mirrors need to be kept clean and insects and other pests kept at bay.

The best PIRs will have dual edge or quad sensing zones and an array that offers a significant number of look down zones, as well as more than one sensing range and the greatest possible number of discrete zones. They’ll have surge and low voltage protection, multiple pyro-electric sensing elements, adjustments letting you alter the range or mask zones, as well as LED-supported latching. Walk-test is another valuable feature.

Once the temperature gets over 35C, any PIR is going to be seriously disadvantaged even if temperature compensation is fattening up that tiny pyro signal through an amplification circuit. If things are going to be warm you should think quality dual technology.

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