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Temperature detection with a PIR sensor

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Temperature detection with a PIR sensor

Marco Genovesi-2

Maybe simple but I haven't any experience of this..
Is it possible to use a common PIR surveillance sensor to detect a warm->cold->warm temperature transition?
I know taht the "normal" use in surveillance is to detect an "hot" body crossing the sensor area.
Instead, I would to detect a cold "object" ( 15-20 C. less than the ambient temperature).
A possible complication is that the cold "object" isn't a solid but really a localized flux of COLD air that rapidly
cross the sensor area and that may be very near ( from 5 to 1 feet from the PIR).
A real case: ambient temperature 25-30 C. and a cold air flux of  5-10 C.


thanks,
Marco
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Re: Temperature detection with a PIR sensor

Olin Lathrop
Marco Genovesi wrote:
> Maybe simple but I haven't any experience of this..
> Is it possible to use a common PIR surveillance sensor to detect a
> warm->cold->warm temperature transition?
> I know taht the "normal" use in surveillance is to detect an "hot"
> body crossing the sensor area.

Actually they work on sensing changes in IR.  They don't specifically detect
hot or cold things, just the pattern moving.  These sensors are really two
sensors inside with the temperature to voltage relationship flipped for the
two.  For any fixed ambient IR hitting both sensors, the result eventually
nulls out.  As the IR field changes, there will be some differential on the
two sensors creating other than the steady state output voltage.  A lens in
front of the sensor roughly focuses the IR image in bands, so that something
of a different temperature moving around hits the two individual sense
points with alternating bands.  The circuit in these things is just a window
detector.

> A possible complication is that the cold "object" isn't a solid but
> really a localized flux of COLD air that rapidly cross the sensor
> area and that may be very near ( from 5 to 1 feet from the PIR).

That's a problem as air is transparent to IR and doesn't exhibit any
significant black body radiation compared to hard stuff in the room.


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Re: Temperature detection with a PIR sensor

alan.b.pearce
>> A possible complication is that the cold "object" isn't a solid but
>> really a localized flux of COLD air that rapidly cross the sensor
>> area and that may be very near ( from 5 to 1 feet from the PIR).
>
>That's a problem as air is transparent to IR and doesn't exhibit any
>significant black body radiation compared to hard stuff in the room.

I heard of someone making a fire sensor that detected the hot air rising
from a very small fire. It was designed for use in a plant, where there
could be a small fire starting, and it was essential to detect it early and
get it under control as the plant used a lot of combustible materials. IIRC
it used a TV camera to sense the image changes due to the shimmer in a
steady image from the hot air rising. Tests showed it could detect a fire
before anyone could see the change in image.


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Re:Temperature detection with a PIR sensor

ivp
In reply to this post by Marco Genovesi-2
> Is it possible to use a common PIR surveillance sensor to detect
> a warm->cold->warm temperature transition?

Think it might be. I tested some PIR circuits a few years ago and
found that cold outside air blowing through the open door into a
warm room was quite apparent on the 'scope and would have
triggered the following logic/micro. But as I wanted only a people
detector this was filtered out with a comparator
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Re: Re:Temperature detection with a PIR sensor

Olin Lathrop
Jinx wrote:
> Think it might be. I tested some PIR circuits a few years ago and
> found that cold outside air blowing through the open door into a
> warm room was quite apparent on the 'scope and would have
> triggered the following logic/micro.

Are you sure you were really measuring the air and not hard objects that it
cooled down?


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Re:Temperature detection with a PIR sensor

Marco Genovesi-2

Olin, thanks for the PIR explanation!
A bit more words for my question. I'm working on an unusual problem, that is
discovering airflow exiting
from small rock cracks on a karst mountain. Caves entrances are often only
small fissures opened in the rock surface and often
hidden by soil debris but maybe evidenced due to the internal-external air
circulation and temperature difference in some seasons
(typically Summer and Winter).  In Summer cave air is generally more cold
than external and these "blowholes" can be detected
due to the cold air flux.  My actual objective is to survey for these in a
somewhat large area mountain flank (rough, 0.5 square miles)
and mapping them with a GPS. I have 2 surveying methods:

1) observing the area from distance (nearest is 600-800 feet)
2) recognizing directly on the terrain

In case (1) I was considering a Thermal IR Camera but price is still
excessive for me even for low-end models.
IR Thermometers have a reasonable cost now  but from that distance (and
without a view-finder and a very spot measue area) the results
seems unreliable.
Case (2) approach is the reason for which I have asked for the PIR sensor:
walking with the PIR looking in ahead, and wait it triggers (a led or
a sound) when sensing a temperature difference. I hope to have explained the
context...

regards,
Marco





----- Original Message -----
From: "Olin Lathrop" <[hidden email]>
To: "Microcontroller discussion list - Public." <[hidden email]>
Sent: Wednesday, April 01, 2009 2:35 PM
Subject: Re: Re:[EE] Temperature detection with a PIR sensor


> Jinx wrote:
>> Think it might be. I tested some PIR circuits a few years ago and
>> found that cold outside air blowing through the open door into a
>> warm room was quite apparent on the 'scope and would have
>> triggered the following logic/micro.
>
> Are you sure you were really measuring the air and not hard objects that
> it
> cooled down?
>
>
> ********************************************************************
> Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
> (978) 742-9014.  Gold level PIC consultants since 2000.
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist 

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Re: Temperature detection with a PIR sensor

Peter
In reply to this post by Olin Lathrop
Olin Lathrop <olin_piclist <at> embedinc.com> writes:
> Are you sure you were really measuring the air and not hard objects that it
> cooled down?

The heat from the exhaled breath of the developer is amply enough to set them
off even when out of the f.o.v. when sensitivity is set high enough.

This is one of the problems with PIRs, they can be set off by sufficiently large
and rapid volumes of air moving by them.

Peter


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Re: Temperature detection with a PIR sensor

Richard Prosser
In reply to this post by Marco Genovesi-2
2009/4/1 Marco Genovesi <[hidden email]>:

>
> Maybe simple but I haven't any experience of this..
> Is it possible to use a common PIR surveillance sensor to detect a warm->cold->warm temperature transition?
> I know taht the "normal" use in surveillance is to detect an "hot" body crossing the sensor area.
> Instead, I would to detect a cold "object" ( 15-20 C. less than the ambient temperature).
> A possible complication is that the cold "object" isn't a solid but really a localized flux of COLD air that rapidly
> cross the sensor area and that may be very near ( from 5 to 1 feet from the PIR).
> A real case: ambient temperature 25-30 C. and a cold air flux of  5-10 C.
>
>
> thanks,
> Marco
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>

I've noticed that my outside sensor often turns the lights on when I
open the garage door in the winter. So the warm air must be setting it
off.

So quite feasible I would think.

RP

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Re: Temperature detection with a PIR sensor

Bob Axtell-3
In reply to this post by Marco Genovesi-2
Actually, there is another way to use PIR.

As a result of the Big Bang, in almost every direction there is a
constant but faint
deep red glow. If you purchase very sensitive PIR detectors, you can
detect a person
as he walks between the sky and the sensor (blocking) at several
hundred feet. Even works in daylight. You will need to search for the
most sensitive detector; I think only the Japanese
make them (Hammatsu-sp?).

--Bob

On Wed, Apr 1, 2009 at 9:15 AM, Marco Genovesi <[hidden email]> wrote:

>
> Olin, thanks for the PIR explanation!
> A bit more words for my question. I'm working on an unusual problem, that is
> discovering airflow exiting
> from small rock cracks on a karst mountain. Caves entrances are often only
> small fissures opened in the rock surface and often
> hidden by soil debris but maybe evidenced due to the internal-external air
> circulation and temperature difference in some seasons
> (typically Summer and Winter).  In Summer cave air is generally more cold
> than external and these "blowholes" can be detected
> due to the cold air flux.  My actual objective is to survey for these in a
> somewhat large area mountain flank (rough, 0.5 square miles)
> and mapping them with a GPS. I have 2 surveying methods:
>
> 1) observing the area from distance (nearest is 600-800 feet)
> 2) recognizing directly on the terrain
>
> In case (1) I was considering a Thermal IR Camera but price is still
> excessive for me even for low-end models.
> IR Thermometers have a reasonable cost now  but from that distance (and
> without a view-finder and a very spot measue area) the results
> seems unreliable.
> Case (2) approach is the reason for which I have asked for the PIR sensor:
> walking with the PIR looking in ahead, and wait it triggers (a led or
> a sound) when sensing a temperature difference. I hope to have explained the
> context...
>
> regards,
> Marco
>
>
>
>
>
> ----- Original Message -----
> From: "Olin Lathrop" <[hidden email]>
> To: "Microcontroller discussion list - Public." <[hidden email]>
> Sent: Wednesday, April 01, 2009 2:35 PM
> Subject: Re: Re:[EE] Temperature detection with a PIR sensor
>
>
>> Jinx wrote:
>>> Think it might be. I tested some PIR circuits a few years ago and
>>> found that cold outside air blowing through the open door into a
>>> warm room was quite apparent on the 'scope and would have
>>> triggered the following logic/micro.
>>
>> Are you sure you were really measuring the air and not hard objects that
>> it
>> cooled down?
>>
>>
>> ********************************************************************
>> Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
>> (978) 742-9014.  Gold level PIC consultants since 2000.
>> --
>> http://www.piclist.com PIC/SX FAQ & list archive
>> View/change your membership options at
>> http://mailman.mit.edu/mailman/listinfo/piclist
>
> --
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> View/change your membership options at
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Re:Temperature detection with a PIR sensor

ivp
In reply to this post by Olin Lathrop
> Are you sure you were really measuring the air and not hard objects
> that it cooled down?

I might suspect that the cold air was getting between the sensor and
the warm objects. I don't know if the temperature of a body of air
can be measured directly, but it could be that its influence on other
things in the environment can be
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Re: Temperature detection with a PIR sensor

Richard Prosser
In reply to this post by Bob Axtell-3
2009/4/2 Bob Axtell <[hidden email]>:

> Actually, there is another way to use PIR.
>
> As a result of the Big Bang, in almost every direction there is a
> constant but faint
> deep red glow. If you purchase very sensitive PIR detectors, you can
> detect a person
> as he walks between the sky and the sensor (blocking) at several
> hundred feet. Even works in daylight. You will need to search for the
> most sensitive detector; I think only the Japanese
> make them (Hammatsu-sp?).
>
> --Bob
>


Bob
If you have a sensor sensitive enough to see the "deep red glow",
wouldn't a person be like a bright torch standing in from of it?

RP
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Re:Temperature detection with a PIR sensor

ivp
In reply to this post by Marco Genovesi-2
> In case (1) I was considering a Thermal IR Camera but price is still
> excessive for me even for low-end models

Can you rent ? You might find it more economic in the long term

> Case (2) approach is the reason for which I have asked for the PIR
> sensor: walking with the PIR looking in ahead, and wait it triggers (a
> led or a sound) when sensing a temperature difference

You'd need a pretty good (Fresnel) lens for detection at 600ft, plus
all the intervening air currents and sensor movements would be quite
disruptive

Another issue is the orientation of the sensor. PIR sensors have two
piezo bars. In horizontal orientation it's like an =. The sensor's built-in
amplifier outputs a difference signal, as first one bar detects PIR, then
the other, as a body moves across the field of view. The maximum
output is when movement is perpendicular to the bar's orientation. ie
a = orientation will best detect vertical movement. That suggests you'd
need more than one sensor, in various orientations, to get maximum
response if you expect these air movements to be at unknown angles
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Re: Temperature detection with a PIR sensor

ivp
In reply to this post by Richard Prosser
Murata have a very good tutorial on PIR detectors, but I can't
find it on their site (yet). I've an old hard copy somewhere

There's information here that will help though

http://www.murata.com/products/catalog/pdf/s21e.pdf

http://www.murata.com/articles/ta0851.pdf


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Re: Temperature detection with a PIR sensor

alan.b.pearce
In reply to this post by Richard Prosser
> As a result of the Big Bang, in almost every direction there is a
> constant but faint
> deep red glow. If you purchase very sensitive PIR detectors, you can
> detect a person
> as he walks between the sky and the sensor (blocking) at several
> hundred feet. Even works in daylight. You will need to search for the
> most sensitive detector; I think only the Japanese
> make them (Hammatsu-sp?).

One of the researchers at the Lab here is using one of those sensors in an
experiment on the peak of Mount Snowdon in the Welsh Highlands. Something to
do with detecting atmospheric disturbances of some kind.

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RE: Temperature detection with a PIR sensor

Michael Rigby-Jones
In reply to this post by ivp


> -----Original Message-----
> From: [hidden email] [mailto:[hidden email]] On
Behalf

> Of Jinx
> Sent: 01 April 2009 21:48
> To: Microcontroller discussion list - Public.
> Subject: Re:[EE] Temperature detection with a PIR sensor
>
> > Are you sure you were really measuring the air and not hard objects
> > that it cooled down?
>
> I might suspect that the cold air was getting between the sensor and
> the warm objects. I don't know if the temperature of a body of air
> can be measured directly, but it could be that its influence on other
> things in the environment can be
> --

It is apparently possible for drafts to set of the PIR sensors used in
security systems.  

ISTR that whilst PIR sensors are only sensitive to changes in incident
radiation, they can be used in conjunction with mechanical choppers to
measure absolute levels.

Regards

Mike

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Re: Temperature detection with a PIR sensor

ivp
> It is apparently possible for drafts to set off the PIR sensors
> used in security systems

In Marco's proposed application it seems as though to detect
events reliably you'd need to know their nature, as compared
with what else is going on. For example, a still warm body in a
still cold room will not cause a detectable output from the PIR,
because the output is the difference signal between the two bars,
and if their inputs are stable, so will be the output. It floats mid-
supply, very much like some of the Hall sensors. When the PIR's
input changes, the slope of the output change imparts some
information about what caused it. Again, much like a Hall sensor

The steeper the slope (ie higher frequency) the greater the difference
between the two bar's signals. This indicates both the speed and
temperature difference, wrt to the stable environment, of the event/
object. A high-pass filter should remove drafts, although PIR's have
a very narrow bandwidth and in a dynamic enviroment this might
not be enough. Depending on the application, digital processing
would be needed to augment the analogue
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Re:Temperature detection with a PIR sensor

Marco Genovesi-2
In reply to this post by ivp

Jinx wrote:
>> Can you rent ? You might find it more economic in the long term

At a first search, I haven't found a valid renter but I'm still on getting
informations..


> You'd need a pretty good (Fresnel) lens for detection at 600ft...

Jinx,  I intended the use of PIR only as "handheld" sensor (better, fixed on
the helmet) while walking
on the terrain,  and so the distance from ground is 6 feet max or even less.
Usually these surveys are done walking as much as possible along the
mountain flank at the same altitude, then climbing up for a while and
walking again but in reverse, and so on... In this mode one can accurately
survey a large area (yes, tedious!) and is easier to "cross" a cold flux of
air exaled by an eventual fissure sited few meters over. When outdoor is
warm, I have noticed that is easy to sense these cold air movements even at
a distance of tens of meters because the cold air silently slip low along
the slope.
So orientation the sensor in the right sense, probably it woud have to
detect a warm -cold transition that maybe enough for triggering if
temperature difference is sufficient... well, some practical tests will be
necessary.

thanks!!
Marco




----- Original Message -----
From: "Jinx" <[hidden email]>
To: "Microcontroller discussion list - Public." <[hidden email]>
Sent: Wednesday, April 01, 2009 11:06 PM
Subject: Re:[EE] Temperature detection with a PIR sensor


>> In case (1) I was considering a Thermal IR Camera but price is still
>> excessive for me even for low-end models
>
> Can you rent ? You might find it more economic in the long term
>
>> Case (2) approach is the reason for which I have asked for the PIR
>> sensor: walking with the PIR looking in ahead, and wait it triggers (a
>> led or a sound) when sensing a temperature difference
>
> You'd need a pretty good (Fresnel) lens for detection at 600ft, plus
> all the intervening air currents and sensor movements would be quite
> disruptive
>
> Another issue is the orientation of the sensor. PIR sensors have two
> piezo bars. In horizontal orientation it's like an =. The sensor's
> built-in
> amplifier outputs a difference signal, as first one bar detects PIR, then
> the other, as a body moves across the field of view. The maximum
> output is when movement is perpendicular to the bar's orientation. ie
> a = orientation will best detect vertical movement. That suggests you'd
> need more than one sensor, in various orientations, to get maximum
> response if you expect these air movements to be at unknown angles
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist 

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Re:Temperature detection with a PIR sensor

ivp
> well, some practical tests will be necessary

You would be able to tell quite quickly whether your method will
work by doing something like opening the fridge or freezer door and
seeing if the cold air flowing out can be detected against the warmer
kitchen. I think though PIR sensors are too slow to react at walking
pace and the signal will be quite "wobbly"
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Re: Re:Temperature detection with a PIR sensor

Marco Genovesi-2

>>I think though PIR sensors are too slow to react at walking
>>pace and the signal will be quite "wobbly"

mmm..may be possible, however today I will buy a small PIR detector for
lighting the income of my house (I need it):  specs says it has a fresnel
lens of 90 degree view and a max. sensing distance of 24 feet. If this don't
detect  the opening of fridge door, I will try a better long-range model..
I will get the results in short time, thanks!

Marco





----- Original Message -----
From: "Jinx" <[hidden email]>
To: "Microcontroller discussion list - Public." <[hidden email]>
Sent: Thursday, April 02, 2009 2:12 AM
Subject: Re:[EE] Temperature detection with a PIR sensor


>> well, some practical tests will be necessary
>
> You would be able to tell quite quickly whether your method will
> work by doing something like opening the fridge or freezer door and
> seeing if the cold air flowing out can be detected against the warmer
> kitchen. I think though PIR sensors are too slow to react at walking
> pace and the signal will be quite "wobbly"
> --
> http://www.piclist.com PIC/SX FAQ & list archive
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Re: Temperature detection with a PIR sensor

V S
In reply to this post by Marco Genovesi-2
Yes, of course. You need a mechanical (or optoelectronical) chopper in
front of your PIR detector.

On 4/1/09, Marco Genovesi <[hidden email]> wrote:

>
> Maybe simple but I haven't any experience of this..
> Is it possible to use a common PIR surveillance sensor to detect a warm->cold->warm temperature transition?
> I know taht the "normal" use in surveillance is to detect an "hot" body crossing the sensor area.
> Instead, I would to detect a cold "object" ( 15-20 C. less than the ambient temperature).
> A possible complication is that the cold "object" isn't a solid but really a localized flux of COLD air that rapidly
> cross the sensor area and that may be very near ( from 5 to 1 feet from the PIR).
> A real case: ambient temperature 25-30 C. and a cold air flux of  5-10 C.
>
>
> thanks,
> Marco
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
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