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'[EE]: Temperature detection with a PIR sensor'
2009\04\01@144242 by Richard Prosser

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2009/4/1 Marco Genovesi <spam_OUTcarroz53TakeThisOuTspamgmail.com>:
>
> 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
>

2009\04\02@070125 by Vasile Surducan

face picon face
Yes, of course. You need a mechanical (or optoelectronical) chopper in
front of your PIR detector.

On 4/1/09, Marco Genovesi <.....carroz53KILLspamspam@spam@gmail.com> wrote:
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> -

2009\04\02@183415 by Marco Genovesi

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Hello Vasile,
as I said to Jinx in the last e-mail,  I was going to buy a PIR detector for
some tests. Oh, a bit "poor-man" detector... but eventually good for
lighting  the income of my house that is always in the shadow-dark. These
are the specs:

case:  plastic, approx. 8x6x3 cm
light: n. 4 white leds wide angle
power: 4.5V (n. 3 AA cells).
PIR sensor with half-spherical fresnel lens
Angle and distace of detection: 100 degree - 5meters
There is also a 3-positions switch (on-off-auto) and a CDS cell that don't
fire
the leds if the lux level is enough.

1) Hair dryer test1:  In the dark - with an hair-dryer lateral to the PIR, I
have directed the (very) warm air  in front of the sensor (distance 40 cm)
moving it rapidlly up and down. Result:  NEGATIVE  (mmm... Olin is right
here... seem that air don't has a valid IR emission!)

2) Hair dryer test 2:    in the dark - hair-dryer was off, but his platic
cap was still hot. As soon as the cap pass in the PIR detection range, the
leds are illuminated (WOW..OK!)

3) Test refrigerator: with slightly opened door (few centimeters), when I
move the PIR accross the door, the leds are illuminated (OK).

4) Yoghourt Test (!):  in the dark - get the yoghout bottle on the kitchen
table. When I move the PIR along the table (1 meter distance) and I cross
the yoghout, the PIR starts the leds (OKK!)

And so on...  Practically, moving the PIR over objects with different
temperature, get the leds on. Apparently, seems there isn't difference if
the object is cold and the surrounding ambient is warm or reverse: the PIR
notice this and works.
If this is right, my original scope may be still possible: the cold air
exiting from a cave entrance isn't sensed but instead is sensed the rock
cooled from the air (and the result is the same for me). Well, next week I
think to do some tests but in the field, with really blowholes and caves.
Thanks a lot who has given suggestions and patience!

Marco






{Original Message removed}

2009\04\02@193818 by Jinx

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> Practically, moving the PIR over objects with different temperature,
> get the leds on

That's great news Marco. I thought you might have some trouble but it
seems the electronics in your unit is doing a good job. Lots of luck with
the great outdoors and let us know how well it works

2009\04\08@071900 by Vasile Surducan

face picon face
Hi Marco,

I've built a termometer with a PIR about 10 years ago. I was able to
sense a difference of temperature of 1C into a cup of tea at 40C.
Warm the tea at 40C, then put some cold water inside and mix  untill
the whole cup content go down to 39C.
Do you want a picture of it? I guess is somewhere on my lab.

As I told you, you need a chopper to modulate the thermal radiation.
Then everything is much sensitive than you can imagine.

Vasile

On 4/3/09, Marco Genovesi <carroz53spamKILLspamgmail.com> wrote:
{Quote hidden}

> {Original Message removed}

2009\04\08@110447 by Michael Algernon

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Vasile  ....  Yes, please post more information.
MA
{Quote hidden}

>> {Original Message removed}

2009\04\08@124208 by Gordon Williams

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An interesting paper on using PIR sensors for horizon detection is at

http://www.ctie.monash.edu.au/hargrave/horizon_sensing_autopilot.pdf

It has a graph of IR frequencies where the atmosphere is opaque and
transparent.

So detecting air temperature rather than a "hard" object temperature may
depend on the frequency of the sensor.  Moisture in the air will also have
significant effects at certain frequencies.

Gordon Williams


{Original Message removed}

2009\04\08@133136 by Dwayne Reid

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I have an old (15 years or so) Fluke IR thermometer attachment for my
DMM.  It works very well.

It has a mechanical shutter that blocks the IR from reaching the
sensor - looks to be about 50% duty cycle with a period of perhaps 300ms.

dwayne


At 05:18 AM 4/8/2009, Vasile Surducan wrote:

{Quote hidden}

--
Dwayne Reid   <dwaynerspamspam_OUTplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax
http://www.trinity-electronics.com
Custom Electronics Design and Manufacturing

2009\04\08@170522 by Richard Prosser

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2009/4/9 Dwayne Reid <@spam@dwaynerKILLspamspamplanet.eon.net>:
{Quote hidden}

Vasile,

What did you make the chopper out of? I.e. how did you manage to
differentiate between the temperature of the chopper and what you were
trying to measure?

Or were you looking for relative measurements as opposed to absolute
temperature?

Richard

2009\04\15@171446 by Marco Genovesi

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Vasile,
sorry for this very late reply but I have been out of home for some days. In
one of these I have tested
my portable PIR led lamp directly in the field, that is a small karst hill
where I know some cave entrances.
Weather was fine in these days, so at 14:00 h.  from two of these a cold
(about 9 C.) airflow exited.
Passing overe the entrance, the PIR sensor easily trigger on, but walking
along the terrain it frequantly triggers
also when apparently there isn't an entrance or an airflow due to a cave: it
probably happens when passing over sunny
rocks or in shadow. Practically, in outdoor it seems too sensitive or has
false triggering....

Maybe it is possible to do some modifications to the internal circuit (it
isn't an smd layout) to reduce the sensitivity
but I'm guessing if this is the right solution for my necessities. How was
your "layout" and why there was the chopper?
(if the PIR sensor is a two-elements I think it is not necessary, right?).

ps: many thanks to all for the replies

Marco




{Original Message removed}

2009\04\15@181423 by Bob Axtell

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I have spent time tinkering with these things, too.

Low frequency IR sensors sense MOTION, not temperature, by detecting
differences between two detector segments inside the PIR sensor. I
doubt that it can be made to detect absolute temperature. People and
animals are detected when they block a colder or warmer
background by moving in front of it. Very sensitive sensors can detect
a blockage when a person or animal blocks emissions from the "Big
Bang".

In general, these things are not very effective. A better detector of
persons at a distance
can be made by studying video camera pixels, then applying a detection
algorithm. But it
draws a LOT more current than a PIR device.

--Bob A

On Wed, Apr 15, 2009 at 2:14 PM, Marco Genovesi <KILLspamcarroz53KILLspamspamgmail.com> wrote:
{Quote hidden}

> {Original Message removed}

2009\04\16@183905 by Marco Genovesi

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Thanks, Bob.
I haven't any practical knowledge about these sensors, just curious to find
for PIR a possible aid in my "research".  As I said in a previous mail,
probably the better
solution is observing the interest area at distance with a thermal IR camera
but the price is still high for me.  Also IR Thermometers seemed attractive
(price is much lower) but I think it is very difficult using them for this
scope. About twenty years ago I had on loan from my office "boss" an Minolta
Cyclops IR thermometer that we was using for motherboard thermal analysis
(very nice unit)!  But testing it at 2-300mt of distance as "cave finder"
wasn't satisfactory: very difficult to understand  temp. values on the
display, always oscillating for every smallest movement of the thermometer.
The only good job was observing relatively big entrances of caves placed on
the opposite wall of a canyon: the spot lens was able to circumscribe the
entire entrance and I was able to know which of them was colder of the
others.

regards,
Marco




{Original Message removed}

2009\04\16@191320 by cdb

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I wonder if some fancy playing with ultrasonic sensors or maybe
microwave detector might work?

Ultrasonics can be used as windspeed detectors, so maybe nulling out
ambient wind speed would leave 'draft' speed from rock holes.
Microwave tx and rx'ing might work the same?

Circuit Cellar had an article on using the Parallax thermopile a few
months ago. The problem with a thermopile would be that you'd need to
calibrate it so it didn't respond to the  background material.

Colin
--
cdb, RemoveMEcolinTakeThisOuTspambtech-online.co.uk on 17/04/2009

Web presence: http://www.btech-online.co.uk  

Hosted by:  http://www.1and1.co.uk/?k_id=7988359







2009\04\16@212327 by Jinx

face picon face
>I wonder if some fancy playing with ultrasonic sensors or maybe
> microwave detector might work?

When Marco first posed the question I thought airport weather
radar. It happened that I'd recently seen one of those Mayday
programs about an air crash caused by a micro downburst

http://en.wikipedia.org/wiki/Downburst

and the subsequent introduction of Doppler radar

Maybe the scale is too small and the expense too large for wind
coming out of caves though

Remember the 'air density detectors' used in Alien ?

blip blip blip "OMG, it's right behind you !!!"

And The Simpsons Santa's-Little-Helper-In-The-Airduct sensor
of course, but I'm sure *that* one is just made-up

2009\04\17@163924 by Marco Genovesi

picon face

Yes, the scale is generally too small altough some long caves "breath" air
up to a speed of 100mph...  this usually happens with small entrances but
30/50
mph airflow are rather common when in-out temperature difference is at
maximum or atmospheric pressure variations are remarkable.
No, I don't think that this can be a really usable method... wearing short
pants is
probably a better solution, as skin of legs is quite sensitive to fresh
air..  ;-)

thanks, ciao
Marco





{Original Message removed}

2009\04\17@181914 by Jinx

face picon face
> Yes, the scale is generally too small altough some long caves "breath"
> air up to a speed of 100mph...  this usually happens with small entrances
> but 30/50 mph airflow are rather common when in-out temperature ....

Marco, if you do manage to find a reliable electronic answer, there's a
ready market in sport. When the America's Cup was last here in NZ, a
couple of friends and I got to thinking about how you could detect the
wind conditions ahead of a yacht. AFAIK no one has done it yet on a
small scale

http://en.wikipedia.org/wiki/Wind_profiler

2009\04\23@034755 by Vasile Surducan

face picon face
On 4/16/09, Bob Axtell <spamBeGonebob.axtellspamBeGonespamgmail.com> wrote:
> I have spent time tinkering with these things, too.
>
> Low frequency IR sensors sense MOTION, not temperature, by detecting
> differences between two detector segments inside the PIR sensor. I
> doubt that it can be made to detect absolute temperature.

Bob, read the Wien Boltzman laws, this will clarify many things for you.

Vasile

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