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Outdoor & Recreation
Camping
Camp alarm - this item may help to keep things secure.
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<blockquote data-quote="Dignit" data-source="post: 361590" data-attributes="member: 5167"><p>Greenhornets device is a PIR - Passive Infra Red device ....... being passive it does not transmit infrared. It only receives infrared. It relies on an infrared sensitive sensor that in its simplest form has a positive side and negative side (there are more sophisticated quad sensors but I won't over complicate the theory explanation). If the ambient infrared red is stable i.e nothing moving the amount of infrared that hits the positive side is the same that hits the negative side and the signals cancel out so there is no triggered alarm. However if something moves through the field of view there is a positive signal followed by a negative signal, or vice versa, and an alarm is triggered. Only problem is anything moving could trigger an alarm, particularly animals or even bushes. You have to be careful what you have them looking at. They typically have adjustments so you can desensitise them by setting multiple +\- pulses before an alarm is triggered.</p><p>It's an interesting fact that everything around us transmits infrared. Something has to be at minus 273 degrees Celsius, absolute zero in degrees Kelvin, for it not to transmit infrared. Infrared is basically light radiation caused by sub-atomic movement.</p></blockquote><p></p>
[QUOTE="Dignit, post: 361590, member: 5167"] Greenhornets device is a PIR - Passive Infra Red device ....... being passive it does not transmit infrared. It only receives infrared. It relies on an infrared sensitive sensor that in its simplest form has a positive side and negative side (there are more sophisticated quad sensors but I won't over complicate the theory explanation). If the ambient infrared red is stable i.e nothing moving the amount of infrared that hits the positive side is the same that hits the negative side and the signals cancel out so there is no triggered alarm. However if something moves through the field of view there is a positive signal followed by a negative signal, or vice versa, and an alarm is triggered. Only problem is anything moving could trigger an alarm, particularly animals or even bushes. You have to be careful what you have them looking at. They typically have adjustments so you can desensitise them by setting multiple +\- pulses before an alarm is triggered. It's an interesting fact that everything around us transmits infrared. Something has to be at minus 273 degrees Celsius, absolute zero in degrees Kelvin, for it not to transmit infrared. Infrared is basically light radiation caused by sub-atomic movement. [/QUOTE]
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Outdoor & Recreation
Camping
Camp alarm - this item may help to keep things secure.
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