You just explained why I can sneak past the detectors when the shop temp is
very high...and it gets VERY hot in here with everything closed-up, even
with 10 hp of vent fans going. I had to go in today and show some stuff to
a potential customer and I wish I had a video of me "sweeping" the plant
with my 9mm Springfield...scared the crap out of the cat. No, I didn't have
to smell Hoppies #9 when I got home.

I'll try an IR source and a fan ainside nd put up some motion detector
lights up outside with some type of noise maker that lets the thieves know
they have been "seen" before they break in.

"Gunner" wrote in message
...
On Fri, 15 Jul 2005 22:27:14 -0700, "PrecisionMachinisT"
wrote:


Pretty sure that's correct....

As I understand it, these sensors pick up "average ir emmision".....this
is
sampled upon some established periodic ( time period )....if /when there
is
some change in total amount ir being recieved that is above (or below )
the
'setpoint' ( perhaps established as an average of the last ten samples or
so)...(and it occurs within too fast of a time frame) then the alarm is
triggered.

--

SVL


Sigh...most PIR detectors have a parabolic mirror element with
multiple segments in multiple aiming paths. An infrared detector
located at the focal point monitors the sum of the incoming infrared.
(or a segmented lens with the detector element facing forwards)

This makes the detector to have detection "fingers"....multple narrow
"alleys" that the detector looks down. A moving heat source when
passing through one of these "alleys", will spike the incoming
infrared..and the detector will trip.

Hold your hand over your desk, with your fingers spread. Your fingers
are the sensitive zones. Now holding a lit match...pass the burning
match under your fingers. Notice the pain occurs only when the match
passes under the sensitive zone ? G

PIR detectors have multiple zones stacked in multiple angles below
horizontal so they may be mounted above normal furniture etc.

Hold your hand out again, fingers spread. Now hold your other hand
below it..fingers spread, and pointing downwards at a 45' angle. We
have just added another layer of detection zones. Call in the wife,
have her add her hands, both with spread fingers and pointing even
farther down. Notice the area is still covered by alleys..but they
start making a rather complex fence. But remember..few PIRS look
straight down..so most have a dead zone below them..and hugging the
wall may defeat detection, directly below the unit.

Something to also consider as you ice your fingers from the match
test..if you had moved the burning match towards and away from your
hand BETWEEN the fingers...you have dead zones where nothing is
detected until you get close to your hand. So when orienting a PIR
device..it should be setup so an intruder has to cross the fingers,
rather than moving towards or away the unit.

There are many units with lens arraignments specifically designed to
look in only one or several directions and angles. If you have pets
for example..a unit mounted in a hallway..with NO downward looking
zones prevents the mogs from tripping the unit.

Some are designed to look in a 360' circle and are to be mounted in
the ceiling in the center of the room, and so forth.

There are some issues with PIR, besides the dead spots between the
detection alleys. The #1 is the Mouse/Elephant Effect. The unit as
we know..is sensitive to sudden changes in detected IR sources. This
means it will detect a mouse at xx inches, or an elephant at .xx
miles.
G
Aiming a PIR unit at an area that has BIG moving heat sources in the
distance..outside for example will cause accidental trips .

The other issue with PIR is and this is less common with newer units
with better detection circuitry..is environmental masking. If the
unit is looking at a wall that is 98.6F..it means each finger is
receiving a heat signature the same as a human body. No detection
unit can operated without false trips if it is only sensitive to a
single "temperature", so internal temperature compensation circuits
will change the sensitivity of the unit as the rooms temperature..or
the background temp changes and over a time period..constantly.

Remember...our detection fingers are looking at walls and floors. As
they change temperature constantly through out the day and night. Lets
say its in a steel building..and the ambient is 80F. One wall is 120F
because the sun is shining on it. Suddenly a cloud passes..and that
wall is no longer being heated. If there were no time/temp
compensation circuity..the walls sudden cooling would generate an
alarm as the detector would suddenly see a change in its input. And
another alarm would occur the moment the cloud passed and the sun
heated the wall again.

The 3rd issue is the lack of sensitivity as the ambient temperature
climbs..overloading the detector. Now it takes an elephant at xx
inches to trigger the unit. Oddly enough..something cold can now
trigger the unit..as its Below ambient..and the detector sees a
negative spike

PIRs are NOT universal units you can stick up anyplace and expect them
to A. Work Every time, and B. Not trip by accident.

Some thought in placement must be used when installing them.
Unfortunately..Ive seen far too many lazy installers stick em up whily
nilly and then leave. The major alarm companies tend to be the worst
offenders for this. Frankly..they want the bucks far more than they
care about providing you with a decent detection system.

And remember folks..a burglar alarm system has NO protection value. It
will NOT protect you from intruders. It will only detect them. Period.
End Program. Full Stop. Next time an alarm co. sales droid comes
calling..ask for a written guarentee that their system will protect
your goods. Chuckle...watch em panic.

Only the Deterent of getting detected and caught keeps the bad guys
away. And if they know that the cops are 45 minutes away..they can be
in and out long before anyone shows up. Gun and pawn shops are
examples of high security, often with multiple alarms by multiple
companies. (eggs in one basket is frowned on in such) and yet a band
of bad guys who steal a truck, ram the front of the business and make
off with a ton of Stuff can get away, unless other provisions are
made..ram proof store fronts, lots of steel and concrete..etc.

Gunner
"Considering the events of recent years,
the world has a long way to go to regain
its credibility and reputation with the US."
unknown

I talked to one of my engineer's son, a cop, about video and he said:
"Great Idea! Just show the video to the inner-city Cleveland cops of some
black men breaking in to your ghetto plant's refrigerators for food and the
cops will run right out and arrest a bunch of them in a city-wide dragnet."

"Jerry Martes" wrote in message
news:0I8Ce.8471$Tx1.5178@trnddc03...

"Tom Gardner" wrote in message
...
I'm still getting broken into almost every weekend again and the thieves
only get the employee's food in the refrigerators and make a mess. I
have
the tools locked-up. We have an ADT system with door contacts and 4
motion detectors. ADT wants $400 for a motion detector so my idea is to
install some or all of the 10 I bought for $14 ea. on a separate system
that triggers a relay to turn on a fan in front of ADT's motion detector.
However, a fan won't trigger the motion detector. I can't "cut-in" to
ADT's system actively so I need to do it passively...any ideas?

(I won't sit down here with a gun, I won't make a batch of Exlax
brownies!
I do have an armed guard service that is in here every couple of hours.)


Tom

If you are interested in seeing who is entering, theres an inexpensive
computer software program called "GOTCHA" that will record pictures on
your
computer whenever the image changes. It was originally designed to
identify whoever entered an area to access some guy's computer.

Jerry

Tom Gardner wrote:
You just explained why I can sneak past the detectors when the shop temp is
very high...and it gets VERY hot in here with everything closed-up, even
with 10 hp of vent fans going. I had to go in today and show some stuff to
a potential customer and I wish I had a video of me "sweeping" the plant
with my 9mm Springfield...scared the crap out of the cat. No, I didn't have
to smell Hoppies #9 when I got home.

I'll try an IR source and a fan ainside nd put up some motion detector
lights up outside with some type of noise maker that lets the thieves know
they have been "seen" before they break in.


snip

Instead of noise, how about a recording.
"Here they come..., you aim for the head, I'll aim for the balls."

--
Gary A. Gorgen | "From ideas to PRODUCTS"
| Tunxis Design Inc.
| Cupertino, Ca. 95014