We have an IR detector light outside our front door. The
detector is angled so that it is not triggered by anybody
walking by and the light is angled so that it only illuminates
our front garden.

But ...

A week or so ago I walked out of the house via the back door,
as usual, down the drive and into the street. As I reached the
far boundary of our property, the light turned on! (The light
and detector focus on the area I'd already walked past,
essentially behind me!)

I looked back at the garden but no sight of a cat or squirrel,
so carried on. When I returned, I walked past the house slowly
and right next to the front wall. The light stayed off.

This was the beginning of the last spell of high winds, mainly
blowing directly at the front of the house, and there were
further instances of the light turning on unexpectedly. Had
the wind altered the position of the detector? I wondered.

Then the winds abated and the light has been working normally.

Today, the wind returned and the light started misbehaving
again. I went out early evening, leaving by the back door as
usual and walking down the drive. The light was already on. I
walked down the street and it stayed on.

A couple of hours later I returned. In the meantime there had
been a heavy downpour and the wind had dropped. I approached
the house - no light - walked close to the wall as I passed
the house - no light - walked down the drive and in the back
door as usual - no light.

Has anybody got any ideas why an IR detector should play up in
the presence of high winds and then work normally when they
drop?

--

Terry

On 10/12/2019 23:47, Terry Casey wrote:
Has anybody got any ideas why an IR detector should play up in
the presence of high winds and then work normally when they
drop?

Mine can sometimes play up from the exhaust from the gas boiler
depending on which way the wind blows, I also have an extractor fan in a
downstairs toilet which if it is cold can set the PIR off when the
toilet is used when the extractor fan kicks out hot air from the toilet.

On 10/12/2019 23:47:02, Terry Casey wrote:

snip

Has anybody got any ideas why an IR detector should play up in
the presence of high winds and then work normally when they
drop?

In high winds most surfaces would become uniform in temperature. Your
coat would quickly become the same the wind temperature.

IR sensors rely on seeing a low frequency temperature variation through
their multiple lenses. If anything is a uniform temperature the sensor
will not provide any output.

"Terry Casey" wrote in message
...

We have an IR detector light outside our front door. The
detector is angled so that it is not triggered by anybody
walking by and the light is angled so that it only illuminates
our front garden.

But ...

A week or so ago I walked out of the house via the back door,
as usual, down the drive and into the street. As I reached the
far boundary of our property, the light turned on! (The light
and detector focus on the area I'd already walked past,
essentially behind me!)

I looked back at the garden but no sight of a cat or squirrel,
so carried on. When I returned, I walked past the house slowly
and right next to the front wall. The light stayed off.

This was the beginning of the last spell of high winds, mainly
blowing directly at the front of the house, and there were
further instances of the light turning on unexpectedly. Had
the wind altered the position of the detector? I wondered.

Then the winds abated and the light has been working normally.

Today, the wind returned and the light started misbehaving
again. I went out early evening, leaving by the back door as
usual and walking down the drive. The light was already on. I
walked down the street and it stayed on.

A couple of hours later I returned. In the meantime there had
been a heavy downpour and the wind had dropped. I approached
the house - no light - walked close to the wall as I passed
the house - no light - walked down the drive and in the back
door as usual - no light.

Has anybody got any ideas why an IR detector should play up in
the presence of high winds and then work normally when they
drop?

Its developed a fault, maybe got water inside.

On Wed, 11 Dec 2019 00:32:16 +0000, Fredxx wrote:

In high winds most surfaces would become uniform in temperature. Your
coat would quickly become the same the wind temperature.

IR sensors rely on seeing a low frequency temperature variation through
their multiple lenses. If anything is a uniform temperature the sensor
will not provide any output.

.... specifically, the field of view is separated into lines or spots by the
lenses. A warm thing moving through the field of view is, as it moves, focused
on the sensor, then not, then focused again, etc. This results in a modulation
of the sensor signal, the frequency depending on the speed and spacing of the
lenses. The sensor is pretty sensitive, to detect a 29° C cat moving across a
25° C background.

Wind alone would not trigger the sensor, if it is all the same temperature
(unless it moves, say, branches, which shade and unshade a warm wall, a
streetlight,

But wind moving a plume of hot air, or itself swirling with subtly different
temperatures could give a similar signal as a warm thing moving across the field
of view, and trigger the sensor.



Thomas Prufer

ss wrote:
On 10/12/2019 23:47, Terry Casey wrote:
Has anybody got any ideas why an IR detector should play up in
the presence of high winds and then work normally when they
drop?

Mine can sometimes play up from the exhaust from the gas boiler
depending on which way the wind blows, I also have an extractor fan in a
downstairs toilet which if it is cold can set the PIR off when the
toilet is used when the extractor fan kicks out hot air from the toilet.


We had a similar problem in a previous house. It was a s*d to diagnose as
there was a gate involved. If the gate was closed, no problem. No
significant wind, no problem. Warm outside, no problem. Eventually I
noticed you needed all three- gate open, wind, cold outside and when the
boiler fired up after dark, the security light came on.

As the gate was intended to be closed the fix was, at least, easy.

The problem is that as far as I am aware PIR devices detect movement by
objects of differing IR emission changing between segments of the sensor.
So warm air if it moves about in front of it can set it off. The same
applies to inanimate objects if they are different temperatures and moving.
In a wind such changes are far more likely to occur as has been mentioned on
here before.


All you can do is adjust sensitivity really, there is no magic solution
since there are so many reasons for differing temperatures.
Brian

--
----- --
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"ss" wrote in message
...
On 10/12/2019 23:47, Terry Casey wrote:
Has anybody got any ideas why an IR detector should play up in
the presence of high winds and then work normally when they
drop?

Mine can sometimes play up from the exhaust from the gas boiler depending
on which way the wind blows, I also have an extractor fan in a downstairs
toilet which if it is cold can set the PIR off when the toilet is used
when the extractor fan kicks out hot air from the toilet.

On 10/12/2019 23:47, Terry Casey wrote:

We have an IR detector light outside our front door. The
detector is angled so that it is not triggered by anybody
walking by and the light is angled so that it only illuminates
our front garden.

But ...

A week or so ago I walked out of the house via the back door,
as usual, down the drive and into the street. As I reached the
far boundary of our property, the light turned on! (The light
and detector focus on the area I'd already walked past,
essentially behind me!)

I looked back at the garden but no sight of a cat or squirrel,
so carried on. When I returned, I walked past the house slowly
and right next to the front wall. The light stayed off.

This was the beginning of the last spell of high winds, mainly
blowing directly at the front of the house, and there were
further instances of the light turning on unexpectedly. Had
the wind altered the position of the detector? I wondered.

Then the winds abated and the light has been working normally.

Today, the wind returned and the light started misbehaving
again. I went out early evening, leaving by the back door as
usual and walking down the drive. The light was already on. I
walked down the street and it stayed on.

A couple of hours later I returned. In the meantime there had
been a heavy downpour and the wind had dropped. I approached
the house - no light - walked close to the wall as I passed
the house - no light - walked down the drive and in the back
door as usual - no light.

Has anybody got any ideas why an IR detector should play up in
the presence of high winds and then work normally when they
drop?


Mine is positioned above the back door. If I leave it open, the hot air
coming out of the house can trigger it. Perhaps it's warm air currents
that's doing it.

Brian
--
Brian

No the lack of output idea does not roll. I have tested this on portable
alarms. Its the movement of differing temperature things that sets them
off, but many have some kind of logic to try and stop the issue. I remember
one particular occasion where a small shrub was partly across a window. The
pir could see the window from its position. As long as there was no wind,
all was well as the window was warmer but always the same place, introduce a
wind though, and the evergreen shrub swayed in front of the window making
the false trigger occur. Re aim the sensor to not see the shrub and all was
well again.
Brian

--
----- --
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"Fredxx" wrote in message
...
On 10/12/2019 23:47:02, Terry Casey wrote:

snip

Has anybody got any ideas why an IR detector should play up in
the presence of high winds and then work normally when they
drop?

In high winds most surfaces would become uniform in temperature. Your coat
would quickly become the same the wind temperature.

IR sensors rely on seeing a low frequency temperature variation through
their multiple lenses. If anything is a uniform temperature the sensor
will not provide any output.

On Wed, 11 Dec 2019 11:38:59 +1100, cantankerous trolling geezer Rodent
Speed, the auto-contradicting senile sociopath, blabbered, again:



Its developed a fault, maybe got water inside.

Are you talking about your brain, senile cretin?

--
Richard addressing Rot Speed:
"**** you're thick/pathetic excuse for a troll."
MID:

Terry Casey wrote:

Has anybody got any ideas why an IR detector should play up in
the presence of high winds

splintered front lens?
wind annoys the spider hiding inside?

On 11/12/2019 06:56, Thomas Prufer wrote:

But wind moving a plume of hot air,


Hot air on its own has not much of a heat signature for the PIR.
The hot air would need particulates in it to be detected hence detecting
the exhaust from a gas boiler etc. In a high wind condition perhaps
more dust is being picked up or the wind chill effect on different
surfaces of protrusions provides the trigger.



--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

On 11/12/2019 07:15, Brian Reay wrote:

We had a similar problem in a previous house. It was a s*d to diagnose as
there was a gate involved. If the gate was closed, no problem. No
significant wind, no problem. Warm outside, no problem. Eventually I
noticed you needed all three- gate open, wind, cold outside and when the
boiler fired up after dark, the security light came on.

As the gate was intended to be closed the fix was, at least, easy.

Positioning PIR detectors can be more of a PITA if they are used for
(indoor) bugler alarm detectors. When I fitted a PIR to detect entrance
into the house via the front door I thought it a good idea to place it
facing the door. Anyone entering the front door would trigger it and I
would then have xx seconds to enter the code so that the alarm wouldn't
sound. Unfortunately what also triggered it was anything being posted
through the letter box, especially on a cold day when the post was cold
and the inside of the house was centrally heated.

I had to reposition the PIR sensor to above the front door so the first
detection happened when anyone was around half way along the hall-way or
just climbing the stairs.

Similar problems can occur if placing the PIR detector facing a window
where anyone walking in front of the window can trigger it - such as the
postman taking a shortcut across your driveway to also deliver to your
neighbour.


--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

On Wednesday, 11 December 2019 09:24:52 UTC, alan_m wrote:

Similar problems can occur if placing the PIR detector facing a window
where anyone walking in front of the window can trigger it - such as the
postman taking a shortcut across your driveway to also deliver to your
neighbour.

I also have had problems with an internal PIR triggering from movement outside a closed window. But other people have told me that's impossible. What's the actual mechanism?

On 10/12/2019 23:47, Terry Casey wrote:


Has anybody got any ideas why an IR detector should play up in
the presence of high winds and then work normally when they
drop?

They are designed to ignore stationary warm objects but if the assembly
is moving in the breeze and there is something warm in its field of view
then its differential detector will see an apparent movement even though
it is the detector swaying in the breeze. It may only take quite a
modest deformation to trigger it. You can sneak up on a PIR if you move
towards it slowly enough and/or wear aluminised clothes.

The other one to check is that there are no spiders hiding inside the
sensor trying to stay warm and dry at this time of year. They are by far
the most common cause of erratic PIR detectors misbehaving.

--
Regards,
Martin Brown

In article , David
wrote:
On Wednesday, 11 December 2019 09:24:52 UTC, alan_m wrote:

Similar problems can occur if placing the PIR detector facing a window
where anyone walking in front of the window can trigger it - such as
the postman taking a shortcut across your driveway to also deliver to
your neighbour.

I also have had problems with an internal PIR triggering from movement
outside a closed window. But other people have told me that's
impossible. What's the actual mechanism?

It may be impossible, but it happens. This is why some manufacturers tell
you to mount them so they can't see out of a window, That's how all mine
are mounted.

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

alan_m wrote:

Positioning PIR detectors can be more of a PITA if they are used for
(indoor) bugler alarm detectors.

Does it warn you if they are about to play Reveille?

Chris
--
Chris J Dixon Nottingham UK
@ChrisJDixon1

Plant amazing Acers.

On 11/12/19 09:48, David wrote:
On Wednesday, 11 December 2019 09:24:52 UTC, alan_m wrote:

Similar problems can occur if placing the PIR detector facing a window
where anyone walking in front of the window can trigger it - such as the
postman taking a shortcut across your driveway to also deliver to your
neighbour.

I also have had problems with an internal PIR triggering from movement outside a closed window. But other people have told me that's impossible. What's the actual mechanism?

https://en.wikipedia.org/wiki/Passive_infrared_sensor#Placement
In particular, the second and third paragraphs.

--

Jeff

We have a PIR on the garage facing a window and it has never been triggered by movement inside the house. In fact it has a remote control which can be used to override the settings or to alter the settings and even that will not work through the window.

Richard

On 11/12/19 13:15, Tricky Dicky wrote:
We have a PIR on the garage facing a window and it has never been triggered by movement inside the house. In fact it has a remote control which can be used to override the settings or to alter the settings and even that will not work through the window.
Really? I just tried the IR remote for the TV in the kitchen through the
double-glazed patio door into the conservatory. Absolutely no problem
changing the volume or channels.

--

Jeff

On 11/12/2019 18:08, Jeff Layman wrote:
On 11/12/19 13:15, Tricky Dicky wrote:
We have a PIR on the garage facing a window and it has never been
triggered by movement inside the house. In fact it has a remote
control which can be used to override the settings or to alter the
settings and even that will not work through the window.
Really? I just tried the IR remote for the TV in the kitchen through the
double-glazed patio door into the conservatory. Absolutely no problem
changing the volume or channels.



It depends on the IR band

Remote controls are in the near IR band up to 1.1 um and can been seen
through a glass lens of a digital camera.

PIR detectors operate in the 8 to 14 um IR band. Most glass is usually
opaque in this band. However the sun shining through the window can heat
the net curtains and passing clouds cause a change in this temperature
triggering the PIR.

Once you go outside of the visible band it may be hard to predict what
may be causing a PIR to trigger. I used to work with and design military
grade IR cameras. A matt varnish on a wood surface could act as a
perfect mirror in IR and items such as black plastic rubbish sacks are
completely transparent.

--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

In article ,
says...

On 10/12/2019 23:47, Terry Casey wrote:
Has anybody got any ideas why an IR detector should play up in
the presence of high winds and then work normally when they
drop?

My thanks to everbody for their suggestions but might I
clarify a few details?

The PIR is on the front of the house and windows are not
involved.

The CH flu is at the rear of the house and emerges through the
roof, so is several feet above the PIR which is below gutter
level. Also, during recent problem periods, it has been on the
leeward end of the house.

The PIR (and lamp) are angled downwards so as to prevent
nuisance to neighbours and false triggering from passing
pedestrians (I can walk along the footway close to the low
front wall without triggering it).

Heating of the wall is not possible - when the sun comes round
to the front of the house it only shines on the outside of the
wall.

There are no trees or bushes within range of the detector,
only some small shrubs which are reasonably wind resistant.

Spiders? Wouldn't they cause problems irrespective of whether
it is windy or not? The PIR is fairly new and, as far as I
know, is well sealed (but I will inspect it closely in
daylight.)


--

Terry

On 11/12/19 19:04, alan_m wrote:
On 11/12/2019 18:08, Jeff Layman wrote:
On 11/12/19 13:15, Tricky Dicky wrote:
We have a PIR on the garage facing a window and it has never been
triggered by movement inside the house. In fact it has a remote
control which can be used to override the settings or to alter the
settings and even that will not work through the window.
Really? I just tried the IR remote for the TV in the kitchen through the
double-glazed patio door into the conservatory. Absolutely no problem
changing the volume or channels.



It depends on the IR band

Remote controls are in the near IR band up to 1.1 um and can been seen
through a glass lens of a digital camera.

Indeed - an easy way to check if the IR led is working using a digital
camera (or smartphone these days!).

I was in fact replying to Tricky Dicky's comment that the remote control
for his PIR sensor didn't seem to work through the window. That seemed
strange to me.

PIR detectors operate in the 8 to 14 um IR band. Most glass is usually
opaque in this band. However the sun shining through the window can heat
the net curtains and passing clouds cause a change in this temperature
triggering the PIR.

I've often wondered if plants behave differently in their ability to
reflect IR light, and that might also add to the variability in
experience people seem to get in what appear to often be similar
situations. Without considering what effect purple, red or yellow-leaves
might have, it seems that even green leaves can vary in their reflectance:
https://calmit.unl.edu/people/agitelson2/pdf/06_JPP-2003.pdf

Once you go outside of the visible band it may be hard to predict what
may be causing a PIR to trigger. I used to work with and design military
grade IR cameras. A matt varnish on a wood surface could act as a
perfect mirror in IR and items such as black plastic rubbish sacks are
completely transparent.

That is interesting. Could you hide a PIR detector inside a black sack
to disguise it?.

--

Jeff

I have been in a care home for two weeks recuperating after an
operation. There was an en-suite bathroom behind a door in my bedroom,
and there was no switch on the light in there. Instead it was turned
on for 5 minutes by PIR movement sensors on both sides of the door.

The door faced my bed, and when I moved, the light came on, shined
through the gaps round the door and woke me up. So i didn't lie on
that side.

I got fed up with this and tried to negate the sensor facing me by
covering it with aly foil, and that stopped the red LED indicator
coming on, but still the light came on when I waved my arms about.

Then I managed to unscrew the faceplate with a tiny key I had, and cut
the wires to the pcb with my nail scissors. Amazingly the light still
came on when I moved my arms about.

Then I covered the sensor on the other side of the door with foil -
still the light came on. I didn't sabotage that sensor because the
light needed to be turned on when someone was in there.

It seems that somehow I was waving warmth through the gaps in the door
and triggering that sensor, even round the foil.

A nurse told me other people had complained, and all the sensors were
on hair trigger. She suggested I should make a complaint via their
residents review app on her tablet, which I did.

I would have disabled the inner sensor temporarily by unscrewing the
terminal block output wire, but I had nothing that would turn the
deep-set screw.
--
Dave W

In article ,
Dave W wrote:
I have been in a care home for two weeks recuperating after an
operation. There was an en-suite bathroom behind a door in my bedroom,
and there was no switch on the light in there. Instead it was turned
on for 5 minutes by PIR movement sensors on both sides of the door.

The door faced my bed, and when I moved, the light came on, shined
through the gaps round the door and woke me up. So i didn't lie on
that side.

I got fed up with this and tried to negate the sensor facing me by
covering it with aly foil, and that stopped the red LED indicator
coming on, but still the light came on when I waved my arms about.

Then I managed to unscrew the faceplate with a tiny key I had, and cut
the wires to the pcb with my nail scissors. Amazingly the light still
came on when I moved my arms about.

Then I covered the sensor on the other side of the door with foil -
still the light came on. I didn't sabotage that sensor because the
light needed to be turned on when someone was in there.

It seems that somehow I was waving warmth through the gaps in the door
and triggering that sensor, even round the foil.

A nurse told me other people had complained, and all the sensors were
on hair trigger. She suggested I should make a complaint via their
residents review app on her tablet, which I did.

I would have disabled the inner sensor temporarily by unscrewing the
terminal block output wire, but I had nothing that would turn the
deep-set screw.

last weekend, I was in a village hall, not mine, and wentb to the loo, The
light came on as I went into the room, I went into thecubilce and closed
the door, after a few seconds the light went out. It didn't come on again
until I opened the door. Luckily there was sufficient daylight coming in
through a window.

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

In article -
september.org, lid says...

Spiders? Wouldn't they cause problems irrespective of whether
it is windy or not? The PIR is fairly new and, as far as I
know, is well sealed (but I will inspect it closely in
daylight.)

I left it for a day to let the monsoon pass over but looked
yesterday.

Absolutely no way for even a momey spider to get in there!

I will have to assume that it is just some of the bushes
moving in the wind. It isn't easy to get to the controls so I
won't bother adjusting the sensitivity as on non high wind
nights it works exactly as we want it to.

--

Terry

In article ,
says...


I would have disabled the inner sensor temporarily by unscrewing the
terminal block output wire, but I had nothing that would turn the
deep-set screw.

So after using all that foil you wre still foiled in the end!

Didn't you think to plug the gap round the door with toilet
paper? I'm sure you could have scrounged some sticky tape (or
plaster!) to hold it in place when the door was opened!


--

Terry

On Sat, 14 Dec 2019 14:08:07 -0000, Terry Casey
wrote:

In article ,
says...


I would have disabled the inner sensor temporarily by unscrewing the
terminal block output wire, but I had nothing that would turn the
deep-set screw.

So after using all that foil you wre still foiled in the end!

Didn't you think to plug the gap round the door with toilet
paper? I'm sure you could have scrounged some sticky tape (or
plaster!) to hold it in place when the door was opened!

I plugged the gap on the top with a towel, but it didn't help, perhaps
because of all the other three gaps.
Dave W

On Sat, 14 Dec 2019 14:08:07 -0000, Terry Casey
wrote:

In article ,
says...


I would have disabled the inner sensor temporarily by unscrewing the
terminal block output wire, but I had nothing that would turn the
deep-set screw.

So after using all that foil you wre still foiled in the end!

Didn't you think to plug the gap round the door with toilet
paper? I'm sure you could have scrounged some sticky tape (or
plaster!) to hold it in place when the door was opened!

If you meant plug the gap to stop the light, I didn't have anything
suitable. I had already looked through all the drawers in the 'Crafts
Room' - not even sticky tape - the foil was kindly brought in by a
visitor and I held it in place with blue-tack borrowed from the
cleaners tick-sheet. The door opens both ways so nothing round the
edge to stop the light. I felt like a prisoner of war.
--
Dave W