SIMPLEARKANSAN, your post on heat motion ...

spectr17

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Your post on heat motion got hit by a glitch in the forum software. It's the thread with no topics and it shows a reply by dharter on 9/3/01. The thread cannot be opened and I can't figure out how to repair it. So, here what was posted posted by you and 4 replies by the time I saw the glitch.


SIMPLEARKANSAN'S Post

HEAT/MOTION DETECTION? DOES THIS DETECT MOTION OR HEAT? MY BUCKSHOT 35 DETECTS HEAT AND MOTION I BELIEVE. I NOTICED THE MENTION OF EVERGREENS HEATING UP AND SETTING OFF THE PIR. IS THE REGENT ALSO HEAT SENSITIVE ALSO?

Possum's reply.

Yes it detects motion & heat.  You can roll a plastic ball in front of it and it will not activate.  You can stand still in front of it and it will not to off.  If you move in front of it BINGO.  But, just like the sensors installed on my house lights, it will go off sometimes if a thunderstorm blows the trees in front of it after they are heated by the sun.PS This goes for both MS20 & RSPIR

SIMPLEARKANSAN'S reply

THANKS FOR YOUR ANSWER. ONE MORE QUESTION THOUGH. IF THE PLASTIC BALL WILL NOT SET IT OFF BECAUSE OF NO HEAT, THEN WHY DOES THE MOTION ALONE NOT SET IT OFF? IF YOU STAND IN FRONT OF THE SENSOR WITHOUT MOTION, YOUR BODY HEAT ALONE WOULDN'T SET IT OFF? DOES IT TAKE A COMBO OF BOTH FACTORS TO TRIP THE SENSOR?

Passthru's reply

exactly,motion and heat.

dharter's reply

The MS20 PIR sensor is charged by heat. The fresnel lens focuses different zones onto the sensor. When a warm body moves from one zone to another there is a varying charge on the output of the PIR. You can see this if you take a laser pointer and point it at the ms20 with the cover off. As you move the laser pointer from left to right, you can see the light move across the PIR.

The output of the PIR goes to an op-amp differentiator. A differentiator is like in calculus.
For a given signal it is the instaneous slope or change of the signal.

The next stage amplifies the signal. The next stage rectifies the signal. That is so the ms20 will be triggered by both increasing charge and decreasing charge.

It also has a comparator with a time constant.
That determines how long the ms20's relay will be on.
 



Tinhorn

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To add to the above and put it in "Other Words"  PIR's work when 2 things happen, as below

1.  (this is the 1st thing)
Warm-Blooded-Animals are actually "Glowing" like a beacon but the light is Infrared, which is not visible to "our" eyes.

2.  The following is the 2nd set of things

A)
Look at the PIR lens, you will see rows of boxes.  Each box is a Magnifiying Lens that will focus the IR Light given off by the animal onto the sensor behind it.  Only one box at a time will see the animal and focus on the sensor.

B)
If the animal is moving across the field of view, there is a "Dead Spot" between boxes (as the focused beam leaves one box and transferrs to the next, there is a dead spot)

C)  So, a moving animal causes a "Pulsating" on the Sensor behind the lens because 1st, there is a Focused Beam on the Sensor then a Dead Spot (No Beam)   The PIR sees something like Morse Code, Dit Dit Dit Dit, as the animal sweeps across all those boxes (Lens)  ----Get It----

To keep down false alarms, PIR's used for burglar alarm systems can be set to go off with either 1, 2, or 3 pulses but I imagine the cheapy MS20,s or RS PIRs are triggered with a single pulse.

*********************************

Okay, so we are glowing like a beacon but the glow is invisible to us?   Some say animals, like Turkey and maybe deer, can see this Infrared too and we are Glowing beacons to them, especially at low light conditions......This is why there are IR inhibitors for our camo

***************************************

Tinhorn
 


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