Passive Infrared Sensors (PIR)
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Passive Infrared (PIR) Motion Sensors protect space by ‘looking’ for changes in infrared (heat) energy levels caused by movement of an intruder. The passive infrared detectors are passive devices. i.e., they do not transmit any form of energy. When a person enters and moves within the detecting zone, his body which is at its normal temperature of 98.6 degree F., radiates more (or less) thermal energy than the surroundings and such minute difference in thermal energy is detected by the PIR. In simple words, PIR keeps a picture of the heat levels in it’s view and keeps on comparing the new view with the stored one. In case there is any change then they activate the alarm. PIR’s come with a wide variety of detection patterns to meet various needs of indoor movement sensing. Depending upon the type of protection needed and the size of the protection area / volume, the specific parameters of angular and area coverage can be chosen from the vast array of PIR types available. The standard PIR has a wide angle coverage with a typical range of 20 to 30 feet. The Narrow angle PIR is for long range covering a long and narrow corridor. The Extra wide angle PIR is for sensing movements through an angle of 150 degrees. When installed outside the entrance, this may be used to warn of any one approaching the entrance. Lighting also can be coupled to come ON automatically along with the chiming / alarming on sensing movements. PIR’s can be used as a stand-alone system (when connected with an output device) or it can also form part of an integrated system along with other types of security devices. If PIR is used as a sensor in a larger Security system which is controlled by a Control Unit (26) , then the Control Unit (26) decides about the action to be taken. Some PIR’s units have a built in key pad to enter the password for activation and deactivation. Some come with a remote control to activate and deactivate. Such PIRs usually have a built in alarm also, which keeps on till it is deactivated. |
