On 2/23/2010 5:56 AM Jim Yanik spake thus:

Phil Hobbs wrote in
:

On 2/21/2010 8:41 PM, David Nebenzahl wrote:

On 2/21/2010 4:12 PM David Nebenzahl spake thus:

I'd like to get responses, ideally, from folks who actually know how
these things work, and not the usual Usenet speculation.

I install a lot of motion-detector lights for clients. A lot of these
installations are problematic. I just adjusted one for the third or
fourth time because the light was staying on all the time, even though
the sensor unit (I replaced the entire unit with a Heath-Zenity sensor
recently) was working properly.

It might help for me to know how, exactly, these sensors work. By
"sensors" I mean the actual sensor, as well asw the entire unit with
the support electronics.

So I found this circuit out there in the wild:

http://www.freeinfosociety.com/elect...ew.php?id=2074

It uses something called a PIR. Does that stand for piezoelectric
infrared? I've seen other references to piezo sensors: how do those
work? Do they both send and receive a signal? (The device shown here is
a 3-terminal thingie.)

Close--pyroelectric, and all pyroelectrics are also piezoelectric,
afaik.

NOPE. PIR=Passive Infra-Red.

Nope.

They can be called that, but they are also called pyroelectric (look it
up if you don't believe me). And no, I don't think they have anything to
do with piezoelectricity; they are, after all, passive elements.


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