How motion sensors work

"William Sommerwerck" wrote in news:hm16p8$flf$ snipped-for-privacy@news.eternal-september.org:

in terms of -sensing-,"passive" means that no radiation is emitted; the sensor depends on existing,external reflected radiation. Unlike say a microwave sensor that emits a signal and detects it's reflection.

Naturally,the sensor itself is going to generate an output signal. (from -some- source of stimulation...)

You guys really ought to give up nitpicking for Lent. They use polyvinylidene fluoride (PVDF) pyroelectric film, which is both piezoelectric and pyroelectric. I used to make similar things for a living (see Footprints,

Do any of you know any _active_ thermal IR detectors?

Cheers

Phil Hobbs

They are 'passive', as opposed to the earlier break beam detectors that were a two piece detector.

I assume you mean that sarcastically. One does not detect a particular form of radiation by _emitting_ it.

Right. So "passive IR detector" is unnecessarily redundant. ;) But it's the nitpicking based on little or no knowledge that I'm teasing them about. (Of course, this being Usenet, I shouldn't be too shocked.)

Cheers

Phil Hobbs

"William Sommerwerck" wrote in news:hm1o6e$lb2$ snipped-for-privacy@news.eternal-september.org:

that's the way microwave detectors work,like the ones at your grocery store or in burglar alarms. the klystron emits uWave radiation and then detects the reflected energy,takes the Doppler difference as an output. OTOH,auto radar detectors are "passive" detectors.

Phil Hobbs wrote in news: snipped-for-privacy@electrooptical.net:

Doesn't matter;the sensors are -still- "passive" detectors.

Not "thermal" IR.

But the technique IS used in other IR wavelengths.

store

These are not microwave detectors, but /motion/ detectors using microwaves.

Please think about it.

"Jim Yanik"

.. Phil

No? What about reflective detection? For example illuminating night scene with IR LEDs and using IR camera and motion detect in software? Not quite the focus on cheap PIRs, but more secure uses are more likely to avoid PIRs' false alarms.

Grant.

form

PIRs'

Let me put this a different way... If you're trying to receive an FM radio station, you do not emit a VHF signal to do so.

The person who posted this comment (see above) agreed with me. There is no such thing as an _active_ thermal IR detector.

They use Gunn diodes, not Klystrons.

On 2/23/2010 6:34 PM William Sommerwerck spake thus:

Nor any other kind of signal.

Therefore all IR detectors are passive. Therefore "passive IR detector" is as redundant as "ATM machine", "PIN number", etc.

Therefore the correct term is *probably* pyroelectric IR detector, just as I said somewhere up there in the receding fogs of this thread ...

A great technology.... Too bad most of the light fixtures you buy now days are garbage. I've got ones that I've put in for clients that have worked for 15 years, and many installed within the last 5 years that have just fallen apart and/or burnt up internally.

Thanks for giving me something to read about tonight...

"William Sommerwerck" wrote in news:hm1the$7er$ snipped-for-privacy@news.eternal-september.org:

Just as the IR sensors are MOTION sensors. Think about it.

You're confusing what the device does with how the sensor works.

"William Sommerwerck" wrote in news:hm3ajq$ogd$ snipped-for-privacy@news.eternal-september.org:

check the topic again.

The infrared sensor in a motion sensor is not the motion sensor itself.

"William Sommerwerck" wrote in news:hm3qkt$gko$ snipped-for-privacy@news.eternal-september.org:

To restate the obvious;the thread's subject is "how motion sensors work".

Clue;It's about sensing MOTION.