How motion sensors work

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in
news:hm3qkt$gko$1@news.eternal-september.org:

These are not microwave detectors, but /motion/ detectors
using microwaves.

Please think about it.

Just as the IR sensors are MOTION sensors. Think about it.

You're confusing what the device does with how the sensor works.

check the topic again.

The infrared sensor in a motion sensor is not the motion sensor itself.
Click to expand...
To restate the obvious;the thread's subject is "how motion sensors work".

Clue;It's about sensing MOTION.

--
Jim Yanik
jyanik
at
localnet
dot com
 
On 2/24/2010 2:38 PM Jim Yanik spake thus:

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in
news:hm3qkt$gko$1@news.eternal-september.org:

These are not microwave detectors, but /motion/ detectors
using microwaves.

Please think about it.

Just as the IR sensors are MOTION sensors. Think about it.

You're confusing what the device does with how the sensor works.

check the topic again.

The infrared sensor in a motion sensor is not the motion sensor itself.

To restate the obvious;the thread's subject is "how motion sensors work".

Clue;It's about sensing MOTION.
Click to expand...
William's right. The whole unit is a motion detector; the PIR is not.
All it does is sense infrared, as its name implies. It's the circuitry
downstream of it that analyzes the deltas and comes up with "Aha!
thermal source moving across my field of view!".


--
You were wrong, and I'm man enough to admit it.

- a Usenet "apology"
 
To restate the obvious; the thread's subject is
"how motion sensors work".
Clue; It's about sensing MOTION.
Click to expand...
That wasn't what we were last discussing, but rather the issue of active
versus passive sensing.
 
"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in
news:hm4j4o$hgf$1@news.eternal-september.org:

To restate the obvious; the thread's subject is
"how motion sensors work".
Clue; It's about sensing MOTION.

That wasn't what we were last discussing, but rather the issue of active
versus passive sensing.
Click to expand...
not relevant to the thread subject.

--
Jim Yanik
jyanik
at
localnet
dot com
 
"Jim Yanik" <jyanik@abuse.gov> wrote in message
news:Xns9D2A55CA5CFDCjyaniklocalnetcom@216.168.3.44...
"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in
news:hm4j4o$hgf$1@news.eternal-september.org:

To restate the obvious; the thread's subject is
"how motion sensors work".
Clue; It's about sensing MOTION.

That wasn't what we were last discussing, but rather
the issue of active versus passive sensing.

Not relevant to the thread subject.
Click to expand...
It might not be (though I feel it is), but it came up.
 
"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in
news:hm5ue9$ls8$1@news.eternal-september.org:

"Jim Yanik" <jyanik@abuse.gov> wrote in message
news:Xns9D2A55CA5CFDCjyaniklocalnetcom@216.168.3.44...
"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in
news:hm4j4o$hgf$1@news.eternal-september.org:

To restate the obvious; the thread's subject is
"how motion sensors work".
Clue; It's about sensing MOTION.

That wasn't what we were last discussing, but rather
the issue of active versus passive sensing.

Not relevant to the thread subject.

It might not be (though I feel it is), but it came up.
Click to expand...
note how the other guy moved the goalposts by asking about "active -
thermal- IR sensors",deliberatly excluding other IR wavelengths that ARE
used in active IR sensing.

--
Jim Yanik
jyanik
at
localnet
dot com
 
Jim Yanik wrote:
"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in
news:hm5ue9$ls8$1@news.eternal-september.org:

"Jim Yanik" <jyanik@abuse.gov> wrote in message
news:Xns9D2A55CA5CFDCjyaniklocalnetcom@216.168.3.44...
"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in
news:hm4j4o$hgf$1@news.eternal-september.org:

To restate the obvious; the thread's subject is
"how motion sensors work".
Clue; It's about sensing MOTION.

That wasn't what we were last discussing, but rather
the issue of active versus passive sensing.

Not relevant to the thread subject.

It might not be (though I feel it is), but it came up.




note how the other guy moved the goalposts by asking about "active -
thermal- IR sensors",deliberatly excluding other IR wavelengths that ARE
used in active IR sensing.
Click to expand...

The other guy? You mean Phil Hobbs. He is an optical engineer.


--
Greed is the root of all eBay.
 
Sansui Samari wrote:
On Feb 23, 2:27 pm, "Michael A. Terrell" <mike.terr...@earthlink.net
wrote:
David Nebenzahl wrote:

Jim Yanik wrote:

NOPE. PIR=Passive Infra-Red.

Nope.

They can be called that, but they are also called pyroelectric (look it
up if you don't believe me). And no, I don't think they have anything to
do with piezoelectricity; they are, after all, passive elements.

They are 'passive', as opposed to the earlier break beam detectors
that were a two piece detector.

--
Greed is the root of all eBay.

A great technology.... Too bad most of the light fixtures you buy now
days are garbage. I've got ones that I've put in for clients that
have worked for 15 years, and many installed within the last 5 years
that have just fallen apart and/or burnt up internally.

Thanks for giving me something to read about tonight...
Click to expand...

Some of the hard wired break beam sensors fed a square wave from the
transmitter to the detector to synchronize them. This prevented ambient
light from tripping them, and also allowed multiple units to be used
where reflections wouldn't cause problems due to differences in the time
period. They were great for lighting controls and for security systems.

They also came with multiple sets of lenses to allow you to select
the beam width, shape and distance. You could shoot one down a long
hallway to turn on the lights whenever anyone stepped into the hallway.
The rest of the time a few night lights gave just enough light to see if
the other lights failed.


--
Greed is the root of all eBay.
 
On Feb 23, 3:27 pm, "Michael A. Terrell" <mike.terr...@earthlink.net>
wrote:
David Nebenzahl wrote:

Jim Yanik wrote:

NOPE. PIR=Passive Infra-Red.

Nope.

They can be called that, but they are also called pyroelectric (look it
up if you don't believe me). And no, I don't think they have anything to
do with piezoelectricity; they are, after all, passive elements.

   They are 'passive', as opposed to the earlier break beam detectors
that were a two piece detector.

--
Greed is the root of all eBay.
Click to expand...
Circuit-wise, it works like this: a light sensor produces a voltage
for a given pattern of light. That voltage is read by a diferentiator
op-amp. The differentiator measures the rate of change of the input
voltage. The output of the differentiator drives a comparator, which
drives a relay to turn on the light.

So, if the light pattern changes, the voltage changes. The op-amp,
which is acting as the brain here, is designed to detect changes in
that sensed voltage with respect to time. In other words, if the op-
amp sees 4V at one time and then 6V one second later, that may be what
is called a "significant change", which is sufficient to activate the
light. However, if the voltage changes from 4V to 6V over the course
of 8 hours, then that rate of change is much slower, and is not likely
to cause the system to switch on.
 
On Feb 23, 3:27 pm, "Michael A. Terrell" <mike.terr...@earthlink.net>
wrote:
David Nebenzahl wrote:

Jim Yanik wrote:

NOPE. PIR=Passive Infra-Red.

Nope.

They can be called that, but they are also called pyroelectric (look it
up if you don't believe me). And no, I don't think they have anything to
do with piezoelectricity; they are, after all, passive elements.

   They are 'passive', as opposed to the earlier break beam detectors
that were a two piece detector.

--
Greed is the root of all eBay.
Click to expand...
If you are interested in the circuitry of these devices, you can buy
the sensors for less than $2.00. The remaining circuitry might cost
you $5.00. http://www.futurlec.com/PIR_Sensors.shtml
 
Andy wrote:
On Feb 23, 3:27 pm, "Michael A. Terrell" <mike.terr...@earthlink.net
wrote:
David Nebenzahl wrote:

Jim Yanik wrote:

NOPE. PIR=Passive Infra-Red.

Nope.

They can be called that, but they are also called pyroelectric (look it
up if you don't believe me). And no, I don't think they have anything to
do with piezoelectricity; they are, after all, passive elements.

They are 'passive', as opposed to the earlier break beam detectors
that were a two piece detector.

--
Greed is the root of all eBay.

If you are interested in the circuitry of these devices, you can buy
the sensors for less than $2.00. The remaining circuitry might cost
you $5.00. http://www.futurlec.com/PIR_Sensors.shtml
Click to expand...

I learned how they work over 25 years ago, but thanks for the link.


--
Greed is the root of all eBay.
 
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