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Old 04-19-2013, 08:13 PM   #1
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12v DC motion sensor...non PIR?


Putting some ambient led lighting underneath a floating vanity in our bathroom, and while shopping for PIR sensors, came to the quick realization that the HVAC duct is about 12" off the floor...about the same height the PIR sensor would be at.

would the air (hot or cold) trigger the PIR sensor? I understand that they trigger on both temprature and motion change?

do I need to look at a different option?

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Old 04-19-2013, 09:09 PM   #2
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12v DC motion sensor...non PIR?


No. They trigger only from moving warm objects. HVAC is stationary, and will not activate it.

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Old 04-19-2013, 09:19 PM   #3
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12v DC motion sensor...non PIR?


Ok thanks. So objects with mass then huh? The hot/cold air blowing wihin the units range wont do it?
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Old 04-20-2013, 01:09 PM   #4
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12v DC motion sensor...non PIR?


Correct, although air does have mass. It detects moving objects emitting IR within a certain range of wavelengths, corresponding to roughly body temperature. So only objects with significant emissivity are detectable. Air is transparent, so it has essentially no emissivity, so there is no IR radiation from the air to detect. The HVAC diffuser will emit, but it's not moving around so the detector will not trigger from it.
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