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'[EE] Temperature detection with a PIR sensor'
2009\04\01@081319 by Jinx

face picon face
> 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

2009\04\01@083524 by olin piclist

face picon face
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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2009\04\01@121554 by Marco Genovesi

picon face

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 removed}

2009\04\01@125121 by Peter

picon face
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


2009\04\01@161110 by Bob Axtell

face picon face
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 <spam_OUTcarroz53TakeThisOuTspamgmail.com> wrote:
{Quote hidden}

> {Original Message removed}

2009\04\01@164827 by Jinx

face picon face
> 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

2009\04\01@170238 by Richard Prosser

picon face
2009/4/2 Bob Axtell <.....bob.axtellKILLspamspam@spam@gmail.com>:
> 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

2009\04\01@170646 by Jinx

face picon face
> 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

2009\04\01@173556 by Jinx

face picon face
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


2009\04\01@174009 by Alan B. Pearce

face picon face
> 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.

2009\04\01@174308 by Michael Rigby-Jones

picon face


> -----Original Message-----
> From: piclist-bouncesspamKILLspammit.edu [.....piclist-bouncesKILLspamspam.....mit.edu] On
Behalf
{Quote hidden}

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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2009\04\01@181447 by Jinx

face picon face
> 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

2009\04\01@194028 by Marco Genovesi

picon face

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 removed}

2009\04\01@204747 by Jinx

face picon face
> 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"

2009\04\02@042641 by Marco Genovesi

picon face

>>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 removed}

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