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'[EE]: photo1 -Temperature detection with a PIR sen'
2009\04\23@034503 by Vasile Surducan

face picon face
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I found (with some difficulty) the prototype. It's here on two
pictures. I hope the server will accept the photos. On front view you
can see the PIR detector, amplifier and chopper. On top view you can
see the FDD stepper (the stepper driver is also there) and the chopper
fixture.
I hope this will give you at least an ideea.

Vasile

On 4/8/09, Michael Algernon <spam_OUTpicTakeThisOuTspamnope9.com> wrote:
{Quote hidden}

> >> {Original Message removed}

2009\04\23@094914 by Peter

picon face
Air does emit IR as anything else does. Its emissivity is low due to low
density, however. Iow, one needs a large amount of warm (not hot) air to make
the PIR see it. Too hot will not be seen, it needs to be at about 30-40 degrees,
and the best way to see it is against the cold night sky, but it *will* be seen
by the PIR. A similar situation can occur when a PIR faces outside in winter and
some hot air comes out of the house and passes in front of it.

Peter

2009\04\23@135410 by Vasile Surducan

face picon face
The ideea is the IR wavelenght. Human IR radiation is different from
air. Water IR emission is different from human body wavelenght. Read
please the physics laws . Usual PIR has a filter for human wavelenght.
Your assumtion is correct unless you are not using a cold reference
(a peltier). It's worthless to discuss more, non contact thermometers
with PIR detectors have been manufactured since the PIR has been
invented. The same principle you can see in the pictures has been used
in rockets heads following any moving hot engines. The only difference
was the sensor sensitivity which was Pb-Se and not PIR. Differential
PIRs are not affected by hot air.

On 4/23/09, Peter <plpeter2006spamKILLspamyahoo.com> wrote:
> Air does emit IR as anything else does. Its emissivity is low due to low
> density, however. Iow, one needs a large amount of warm (not hot) air to make
> the PIR see it. Too hot will not be seen, it needs to be at about 30-40 degrees,
> and the best way to see it is against the cold night sky, but it *will* be seen
> by the PIR. A similar situation can occur when a PIR faces outside in winter and
> some hot air comes out of the house and passes in front of it.
>
> Peter
>
> -

2009\04\23@145501 by Peter

picon face
Vasile Surducan <piclist9 <at> gmail.com> writes:
> The ideea is the IR wavelenght. Human IR radiation is different from
> air. Water IR emission is different from human body wavelenght.

?! Next you will tell me colored people emit differently from whites ? It's
blackbody radiation, and everything emits it and absorbs it. With the exception
of some semiconductors and non-linear optical materials, most materials emit as
nearly pure black bodies at the temperatures considered (~ 37 deg C +/- 10).
That includes air. The emissivity is determined among other things by density
and imaged area.

Differential PIRs will sense a beam or jet of different temperature air (or any
gas or liquid) when passing in front of them, as long as it forms an image on
the sensor. Due to the low density of air, a constant background is needed, and
the jet must be rather large by volume. Normal alarm PIRs filter such inputs out
but if one connects a scope to the analog PIR preamp output one can see even
one's own breath as it passes in front of the sensor (which must be shielded
with something *transparent* at 3 to 10um to avoid direct air current
influences, and with the differential half shielded off - the contrast of a
bubble of warm air is not sufficient when both halves can 'see'). The signal is
small (say 1/20 of normal output when say a hand passes in front of it).

Cooling the sensor is needed for S/N, contrast and speed reasons, if both the
target and the background are cooler than the sensor. In any case, it is enough
to cool the sensor below the temperature of the hotter of the two (target or
background). Afaik modern 'all aspect ratio' anti-aircraft missiles 'see' the
jet exhaust plume (gases) behind the aircraft, and any hot parts thereon (like
the engine cowling). Most seem to work without cryogenics now (or use single use
chemical cartridge coolers or whatever), according to web data.

 Peter


2009\04\23@153551 by olin piclist

face picon face
Peter wrote:
> Next you will tell me colored people emit differently from whites

Well, actually, yes.  Think about it.  If they didn't you couldn't
distinguish them by color.  It may be that there is little distinction in
the IR range, but there could be since there certainly is in the visible
range.

> It's blackbody radiation, and everything emits it and absorbs it.

No, only truly black bodies do.  Everything else emits and absorbes less.
That's why air, being transparent to IR, emits virtually no IR itself.  It
can, however, warm or cool things it contacts and cause them to emit a
different IR signature.  Pockets of hotter or colder air will also refract
light, so such pockets moving in front of a IR sensor can make it look like
the IR coming from the objects behind the pockets is changing.  This is the
same effect as when you see "shimmering heat" off the highway in front of
you in the summer.  You're not seeing the hot air, but you are seeing the
refraction effects of the thermal gradients in the air.


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2009\04\23@170514 by Peter

picon face
Olin Lathrop <olin_piclist <at> embedinc.com> writes:
> > It's blackbody radiation, and everything emits it and absorbs it.
> No, only truly black bodies do.  Everything else emits and absorbes less.

Less is true, but not by much. Melanine, the pigment responsible for human skin
pigmentation, is hardly an optically inactive substance, it is in fact *very*
active and its emissivity is very definitely un-blackbody-like afaik (but I do
not know in infra-red). Most complex proteins that have some *color* share this
property, among other things. Afaik that is one of the ways to look for 'life'
and plant coverage in remote sensing applications, the light emitted and
reflected by lifeforms has some serious absorbtion and emission (fluorescence)
dips and peaks in the expected blackbody plot.

> That's why air, being transparent to IR, emits virtually no IR itself.  It

Actually gases and transparent objects in general *do* emit blackbody radiation
like everything else. Transparency and emissivity are two almost unrelated
properties, as you have worked with computer graphics you should know that (in
extremes one can generate computer models of 3d ray traceable lights and halos
that are transparent yet emit quite fine). The 20K 'background radiation' of the
known sky is due mostly to this apparently.

One of the oldest IR detectors is the Luft detector which consists of a
sensitive microphone placed in a closed chamber filled with gas (CO2 f. ex.) and
an optically chopped radiation input through a window. Works great (for the
1950s when it was all the rage and before that). The gas absorbs the radiation,
heats up and expands, then cools down and  contracts with the chopper rhythm,
creating an output on the microphone. The chamber is usually differential with
the two chambers being lit alternately and the microphone sensing differential
pressure between the chambers. The gas used selects the wavelength and the
*pressure* (thus density) is chosen as high as possible to increase sensitivity
(at the expense of the narrowness of the absorption band).

> can, however, warm or cool things it contacts and cause them to emit a
> different IR signature.  Pockets of hotter or colder air will also refract
> light, so such pockets moving in front of a IR sensor can make it look like
> the IR coming from the objects behind the pockets is changing.  This is the

Also true, but likely not the reason for the readouts from the PIR, which were
the same against the night sky as against the ceiling (in both cases detecting
breath air quite well, but under the designed pulse amplitude discriminator
threshold).

Peter


2009\04\23@183454 by olin piclist

face picon face
Peter wrote:
> Olin Lathrop <olin_piclist <at> embedinc.com> writes:
>>> It's blackbody radiation, and everything emits it and absorbs it.
>> No, only truly black bodies do.  Everything else emits and absorbes
>> less.
>
> Less is true, but not by much. Melanine, ...

I was talking about physics here, not specific pigments (and it's melanin,
melanine is a kind of plastic).  Also, the less than black body can be
substantial.  Common white paper absorbs only about 15% of the visible light
that a truly black piece of paper would, for example.  And many things are
more reflective than common white paper.

> Actually gases and transparent objects in general *do* emit blackbody
> radiation like everything else. Transparency and emissivity are two
> almost unrelated properties,

Completely wrong.  Go back and check your freshman physics.  Put in terms
you may be more familiar with, any antenna works equally well or poorly
whether receiving or transmitting.  There is no such thing as a one way
antenna.  This doesn't change when the wavelength gets a bit shorter.

Think about it.  If this weren't true you could violate thermodynamics and
build free energy machines.  Put any object that emits differently than it
obsorbs into a vacuum inside a glass housing on your desk.  If it absorbed
more than it transmits, then its equillibrium temperature would be higher
than the surroundings.  If it transmitted more than it absorbed, its
equillibrium temperature would be lower.  Either way you'd be getting free
energy when there isn't any to be had.

Air, like everything else, emits IR just as well or poorly as it absorbs it.
Since air is pretty much transparent to IR, it can't be radiating it either.
It will radiate a tiny amount, due to impurities like dust and to the extent
it's not fully 100% transparent.

> as you have worked with computer
> graphics you should know that (in extremes one can generate computer
> models of 3d ray traceable lights and halos that are transparent yet
> emit quite fine).

This means nothing of course.  I can do all sorts of things in computer
graphics that violate physical reality.  Just because you can draw a picture
of something doesn't make it real.  Do you believe in Homer Simpson and
Sponge Bob talking underwater too, let alone a sponge with arms sticking out
speaking english?


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(978) 742-9014.  Gold level PIC consultants since 2000.

2009\04\23@221219 by Robert A LaBudde

flavicon
face
At 06:35 PM 4/23/2009, Olin wrote:
><snip>
>Think about it.  If this weren't true you could violate thermodynamics and
>build free energy machines.  Put any object that emits differently than it
>obsorbs into a vacuum inside a glass housing on your desk.  If it absorbed
>more than it transmits, then its equillibrium temperature would be higher
>than the surroundings.  If it transmitted more than it absorbed, its
>equillibrium temperature would be lower.  Either way you'd be getting free
>energy when there isn't any to be had.
><snip>

Isn't light energy? I think the first law of thermodynamics is still safe!

================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: .....ralKILLspamspam.....lcfltd.com
Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
824 Timberlake Drive                     Tel: 757-467-0954
Virginia Beach, VA 23464-3239            Fax: 757-467-2947

"Vere scire est per causas scire"
================================================================

2009\04\23@222220 by Marechiare

picon face
>> Next you will tell me colored people emit differently from whites
>
> Well, actually, yes.  Think about it.  If they didn't you couldn't
> distinguish them by color.

I am not sure, but you seem to confuse emitting with
reflecting/absorbing. Humans regardless of their scin color emit zero
in visible light, so your ability to distinguish them by color does
not depend on their emitting capabilities which are zero for all.


>> It's blackbody radiation, and everything emits it and absorbs it.
>
> No, only truly black bodies do.  Everything else emits and absorbes less.

I am not sure again, normal glass emits zero UV light but absorbs it
quite well (heck, otherwise they would not use quartz glass in UV
erasable PICs)


> This is the same effect as when you see "shimmering
> heat" off the highway in front of you in the summer.
> You're not seeing the hot air, but you are seeing the
> refraction effects of the thermal gradients in the air.

Refraction effects of the thermal gradients in the air at such
distances? I am not sure, but Sun itself, being a rather hot "air",
emits, not refracts.

2009\04\24@002502 by Peter

picon face
All non-linear optical materials have quantic energy transitions and/or
absorption in some 'interesting' band. Most colored proteins and enzymes are in
this category, including Melanin (without a second e), which is specialized in
UV absorption.

http://omlc.ogi.edu/news/jan98/skinoptics.html
http://www.cl.cam.ac.uk/~jgd1000/melanin.html

Other interesting biologically significant molecules:

www.chm.bris.ac.uk/motm/chlorophyll/chlorophyll_h.htm
http://omlc.ogi.edu/spectra/hemoglobin/
http://omlc.ogi.edu/spectra/PhotochemCAD/html/beta-carotene.html

http://www.chemguide.co.uk/analysis/uvvisible/theory.html

*Most* biologically significant molecules have significantly non-linear spectra.

Many of them will perform energy conversion functions, resulting in the
absorption of light quanta that cause molecule energy state changes that are not
reversible without other inferences (like splitting H2O into H and O ions via a
complex enzyme chain for chlorophyll). This results, among other things, in the
spectrum of the re-radiated energy being significantly different from that of
the incident energy. A typical example is the frequency doubler crystal used in
'green' lasers. Conversely, a free electron laser creates coherent radiation
normally associated with lasing molecules without using any kind of molecules,
in high vacuum.

All molecules are in thermal equilibrium with their neighbors and with incident
radiation, and radiate with peak wavelength at the blackbody wavelength
determined by their temperature. That includes air and all gases.

A commercial PIR device is quite sensitive and does react to the small amount of
IR radiation emitted by sufficient amounts of hot air or gas passing in front of
it, when the background is suitaby different and when the differential
compensation is deleted by oscuring half the detector with Al tape.

Let's stop this nonsense. Anyone can check reality with a scope. I will not
answer any more postings on this thread.

Peter


2009\04\24@074522 by olin piclist

face picon face
Robert A LaBudde wrote:
>> Think about it.  If this weren't true you could violate
>> thermodynamics and build free energy machines.  Put any object that
>> emits differently than it obsorbs into a vacuum inside a glass
>> housing on your desk.  If it absorbed more than it transmits, then
>> its equillibrium temperature would be higher than the surroundings.
>> If it transmitted more than it absorbed, its equillibrium
>> temperature would be lower.  Either way you'd be getting free energy
>> when there isn't any to be had.
>
> Isn't light energy? I think the first law of thermodynamics is still
> safe!

I never said the first law of thermodynamics wasn't safe.  Did you actually
read what I wrote?  I was showing how Peter's claim that absorbtion and
emission aren't linked violates the first law of thermodynamics.  I'm
missing whatever point you are trying to make here.


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Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2009\04\24@075905 by olin piclist

face picon face
Marechiare wrote:
>> No, only truly black bodies do. Everything else emits and absorbes
>> less.
>
> I am not sure again, normal glass emits zero UV light but absorbs it
> quite well (heck, otherwise they would not use quartz glass in UV
> erasable PICs)

Then that same ordinary glass would emit UV as black body radiation if hot
enough, assuming of course its structure hasn't changed from the heat to the
point where it is effectively a different material.

>> This is the same effect as when you see "shimmering
>> heat" off the highway in front of you in the summer.
>> You're not seeing the hot air, but you are seeing the
>> refraction effects of the thermal gradients in the air.
>
> Refraction effects of the thermal gradients in the air at such
> distances?

Yes.  Distance has nothing to do with refraction.  In fact, slight
refraction is easier to see at a distance since the difference between the
refracted and unrefracted light paths get bigger as you get farther away
from the refraction.

> I am not sure, but Sun itself, being a rather hot "air",
> emits, not refracts.

Obviously it emits, but how can you say its atmosphere doesn't refract?
Note also that what I'm talking about with shimmering heat is differential
refraction.  If all the air were the same temperature, the index of
refraction of that air would be the same everywhere and there would be no
bending of light.  Refraction happens at the interface between material with
different indexes of refraction.  Hot and cold air have slightly different
indexes, thereby causing the refraction we see as shimmering when different
cells of hot and cold air move around.

This is the same reason stars appear to dance around when viewed with a
optical telescope from the ground, sometimes known as the "twinkling" star
effect.  Cells of different temperature air pass between the telescope and
the star, refracting the light and making the direction to the star appear
to change.  Look up the Keck telescope in Hawaii.  They have gone to great l
engths with adaptive optics to try to correct for this in real time, with
considerable success.  This is also one substantial advantage of the Hubble
telescope, since there is no atmosphere between it and the remote objects it
is viewing.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2009\04\24@080940 by olin piclist

face picon face
Peter wrote:
> All non-linear optical materials have quantic energy transitions
> and/or absorption in some 'interesting' band.

But we were talking about IR emission of air due to its temperature, which
is black body radiation.  What you are talking about is basically
phosphorescence.  Unless you're arguing that air is phosphorescing in this
case, this point is immaterial.

> A commercial PIR device is quite sensitive and does react to the
> small amount of IR radiation emitted by sufficient amounts of hot air
> or gas passing in front of it,

That's the point of the argument.  Simply stating it again doesn't make it
correct.  I suspect either:

1 - You are just plain wrong and this effect isn't observed.

or

2 - You are seeing some other effect due to different temperature air moving
around, such as refraction, or the air heating/cooling objects the PIR
sensor can "see".


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2009\04\25@093328 by Marechiare

picon face
> This is the same reason stars appear to dance around when viewed with a
> optical telescope from the ground, sometimes known as the "twinkling" star
> effect.  Cells of different temperature air pass between the telescope and
> the star, refracting the light and making the direction to the star appear
> to change.

Yes,
Thanks.

2009\04\26@130037 by Peter

picon face
Vasile Surducan <piclist9 <at> gmail.com> writes:
> I found (with some difficulty) the prototype. It's here on two
> pictures. I hope the server will accept the photos. On front view you

Vasile, why did you orient the detector as you did ? To fit the holes in the
board, or ... ? The orientation is a little odd for how I know the PIR elements
to be laid out inside ?

Peter

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