Function of photocell on operation of PIR?

B

Bill Woods

Guest
I have a PIR motion detector designed to sense if someone is walking
towards my house.

In addition to a dial for adjusting PIR sensitivity, this motion
detector unit has a photocell mounted to face downwards. The motion
detector unit is designed for 24 hour operation so clearly the
photocell is NOT for sensing darkness for "night time only"
operation.

So what does the photocell do?

Unfortunately I can't test it reliably under light and dark
conditions because it is a wirefree detector unit which transmits
pulses every few seconds and gives very sporadic responses.

I figure the photocell probably alters the PIR's sensitivity
charactersistics in some way. Is this right?

But would the unit be made more sensitive or less sensitive in
brighter daylight?
 
Bill Woods wrote:

I have a PIR motion detector designed to sense if someone is walking
towards my house.

In addition to a dial for adjusting PIR sensitivity, this motion
detector unit has a photocell mounted to face downwards. The motion
detector unit is designed for 24 hour operation so clearly the
photocell is NOT for sensing darkness for "night time only"
operation.

So what does the photocell do?

Unfortunately I can't test it reliably under light and dark
conditions because it is a wirefree detector unit which transmits
pulses every few seconds and gives very sporadic responses.

I figure the photocell probably alters the PIR's sensitivity
charactersistics in some way. Is this right?

But would the unit be made more sensitive or less sensitive in
brighter daylight?
Click to expand...
Its more than likely that the motion sensor and the photocell are wired
in series, and the output taken from the centre of them.

The resistance varies WILDLY with ambient light, and this arrangement
allows a basic comparison between them.

Then AC couple that to detect the d/dt of the lot and you are in business.
 
"Bill Woods" <woods_b@emercom.com> wrote in message
news:96447DCF9F01F51D7E@204.153.244.156...
I have a PIR motion detector designed to sense if someone is walking
towards my house.

In addition to a dial for adjusting PIR sensitivity, this motion
detector unit has a photocell mounted to face downwards. The motion
detector unit is designed for 24 hour operation so clearly the
photocell is NOT for sensing darkness for "night time only"
operation.

So what does the photocell do?

Unfortunately I can't test it reliably under light and dark
conditions because it is a wirefree detector unit which transmits
pulses every few seconds and gives very sporadic responses.

I figure the photocell probably alters the PIR's sensitivity
charactersistics in some way. Is this right?

But would the unit be made more sensitive or less sensitive in
brighter daylight?
Click to expand...
All of the fixtures that I have seen that are motion only, do not have a
photo cell. Sort of dumb turning on a light in the day time. My porch
fixture has a photo cell and motion detector. I do not have a adjustment on
the photocell. I try to keep the sensitivity down so that anyone on the
sidewalk does not trigger it. A couple of steps into the yard and it will
turn on. I leave the fixture on all of the time so in the evenings when it
starts getting dark the motion sensor takes over and will turn the light on
according to my settings.
 
On Tue 26 Apr 2005 17:12:29, AlanBown wrote:
<news:MLtbe.44$aA2.1010@news.uswest.net>

"Bill Woods" <woods_b@emercom.com> wrote in message
news:96447DCF9F01F51D7E@204.153.244.156...
I have a PIR motion detector designed to sense if someone is
walking towards my house.

In addition to a dial for adjusting PIR sensitivity, this
motion detector unit has a photocell mounted to face downwards.
The motion detector unit is designed for 24 hour operation so
clearly the photocell is NOT for sensing darkness for "night
time only" operation.

So what does the photocell do?

Unfortunately I can't test it reliably under light and dark
conditions because it is a wirefree detector unit which
transmits pulses every few seconds and gives very sporadic
responses.

I figure the photocell probably alters the PIR's sensitivity
charactersistics in some way. Is this right?

But would the unit be made more sensitive or less sensitive in
brighter daylight?

All of the fixtures that I have seen that are motion only, do
not have a photo cell. Sort of dumb turning on a light in the
day time.
Click to expand...
I too thought a daytime lamp was silly but it works rather well:

When the PIR is tripped, the unit makes a loud sound. If you plug
a lamp into the mains socket on the unit then power is sent to
that socket. You might have a red bulb in your study and get a
visual alarm that someone is approaching. Could be useful if you
didn't want them to hear the audio alarm.


My porch fixture has a photo cell and motion
detector. I do not have a adjustment on the photocell.
Click to expand...
Sounds a bit like mine. What do you find the photocell does to
the PIR's ability to sense people in different conditions of
ambient light?

I try to
keep the sensitivity down so that anyone on the sidewalk does
not trigger it. A couple of steps into the yard and it will turn
on. I leave the fixture on all of the time so in the evenings
when it starts getting dark the motion sensor takes over and
will turn the light on according to my settings.
Click to expand...
The unit I describe sounds more of an alarm.

Your unit lights a lamp and seems more as a warning to intruders
or a courtesy to visitors.
 
"Bill Woods" <woods_b@emercom.com> wrote in message
news:96447DCF9F01F51D7E@204.153.244.156...
I have a PIR motion detector designed to sense if someone is walking
towards my house.

In addition to a dial for adjusting PIR sensitivity, this motion
detector unit has a photocell mounted to face downwards. The motion
detector unit is designed for 24 hour operation so clearly the
photocell is NOT for sensing darkness for "night time only"
operation.

So what does the photocell do?

Unfortunately I can't test it reliably under light and dark
conditions because it is a wirefree detector unit which transmits
pulses every few seconds and gives very sporadic responses.

I figure the photocell probably alters the PIR's sensitivity
charactersistics in some way. Is this right?

But would the unit be made more sensitive or less sensitive in
brighter daylight?
Click to expand...
The photocell is nothing to do with varying the sensitivity of the device -
it is there to detect 'darkness'.
Commonly these things are arranged so that the pir triggers a lamp of some
for some fixed time, to illuminate a path for example, but such illumination
is not required in daylight.
The position and direction of view the photocell (most frequently actually
either a photo-resistor or a photo-transistor) depends on the combined
optical characteristics of the housing, lensing, and photo device. Pointing
down is the most common way of getting the best average ambient illumination
level. Pointing up almost never is.
 
On Tue 26 Apr 2005 21:55:12, R.Lewis wrote:
<news:d4m9nj$8ke$1@domitilla.aioe.org>

"Bill Woods" <woods_b@emercom.com> wrote in message
news:96447DCF9F01F51D7E@204.153.244.156...
I have a PIR motion detector designed to sense if someone is
walking towards my house.

In addition to a dial for adjusting PIR sensitivity, this
motion detector unit has a photocell mounted to face downwards.
The motion detector unit is designed for 24 hour operation so
clearly the photocell is NOT for sensing darkness for "night
time only" operation.

So what does the photocell do?

Unfortunately I can't test it reliably under light and dark
conditions because it is a wirefree detector unit which
transmits pulses every few seconds and gives very sporadic
responses.

I figure the photocell probably alters the PIR's sensitivity
charactersistics in some way. Is this right?

But would the unit be made more sensitive or less sensitive in
brighter daylight?

The photocell is nothing to do with varying the sensitivity of
the device - it is there to detect 'darkness'.
Commonly these things are arranged so that the pir triggers a
lamp of some for some fixed time, to illuminate a path for
example, but such illumination is not required in daylight.
The position and direction of view the photocell (most
frequently actually either a photo-resistor or a
photo-transistor) depends on the combined optical
characteristics of the housing, lensing, and photo device.
Pointing down is the most common way of getting the best average
ambient illumination level. Pointing up almost never is.
Click to expand...
I think you may have skipped too lightly over where I say that the
motion detector unit is designed for 24 hour operation so clearly
the photocell is not for sensing darkness for "night time only"
operation.
 
I have to ask why do you say that the photocell cannot be to detect light or
dark. you say that it is 24 hour operation. All pir operated lights are for
24 hour operation, the pir operates 24 hours, the photocell decides whether
it switches the light on or not.

"Bill Woods" <woods_b@emercom.com> wrote in message
news:9645F0313AC351D7E@204.153.244.156...
On Tue 26 Apr 2005 21:55:12, R.Lewis wrote:
news:d4m9nj$8ke$1@domitilla.aioe.org

"Bill Woods" <woods_b@emercom.com> wrote in message
news:96447DCF9F01F51D7E@204.153.244.156...
I have a PIR motion detector designed to sense if someone is
walking towards my house.

In addition to a dial for adjusting PIR sensitivity, this
motion detector unit has a photocell mounted to face downwards.
The motion detector unit is designed for 24 hour operation so
clearly the photocell is NOT for sensing darkness for "night
time only" operation.

So what does the photocell do?

Unfortunately I can't test it reliably under light and dark
conditions because it is a wirefree detector unit which
transmits pulses every few seconds and gives very sporadic
responses.

I figure the photocell probably alters the PIR's sensitivity
charactersistics in some way. Is this right?

But would the unit be made more sensitive or less sensitive in
brighter daylight?

The photocell is nothing to do with varying the sensitivity of
the device - it is there to detect 'darkness'.
Commonly these things are arranged so that the pir triggers a
lamp of some for some fixed time, to illuminate a path for
example, but such illumination is not required in daylight.
The position and direction of view the photocell (most
frequently actually either a photo-resistor or a
photo-transistor) depends on the combined optical
characteristics of the housing, lensing, and photo device.
Pointing down is the most common way of getting the best average
ambient illumination level. Pointing up almost never is.


I think you may have skipped too lightly over where I say that the
motion detector unit is designed for 24 hour operation so clearly
the photocell is not for sensing darkness for "night time only"
operation.
Click to expand...
 
BIG NIGE wrote:

I have to ask why do you say that the photocell cannot be to detect light or
dark. you say that it is 24 hour operation. All pir operated lights
Click to expand...
He never said it was a PIR operated light.

In fact I assumed it was part of an alarm system.


are for
24 hour operation, the pir operates 24 hours, the photocell decides whether
it switches the light on or not.

"Bill Woods" <woods_b@emercom.com> wrote in message
news:9645F0313AC351D7E@204.153.244.156...

On Tue 26 Apr 2005 21:55:12, R.Lewis wrote:
news:d4m9nj$8ke$1@domitilla.aioe.org

"Bill Woods" <woods_b@emercom.com> wrote in message
news:96447DCF9F01F51D7E@204.153.244.156...

I have a PIR motion detector designed to sense if someone is
walking towards my house.

In addition to a dial for adjusting PIR sensitivity, this
motion detector unit has a photocell mounted to face downwards.
The motion detector unit is designed for 24 hour operation so
clearly the photocell is NOT for sensing darkness for "night
time only" operation.

So what does the photocell do?

Unfortunately I can't test it reliably under light and dark
conditions because it is a wirefree detector unit which
transmits pulses every few seconds and gives very sporadic
responses.

I figure the photocell probably alters the PIR's sensitivity
charactersistics in some way. Is this right?

But would the unit be made more sensitive or less sensitive in
brighter daylight?

The photocell is nothing to do with varying the sensitivity of
the device - it is there to detect 'darkness'.
Commonly these things are arranged so that the pir triggers a
lamp of some for some fixed time, to illuminate a path for
example, but such illumination is not required in daylight.
The position and direction of view the photocell (most
frequently actually either a photo-resistor or a
photo-transistor) depends on the combined optical
characteristics of the housing, lensing, and photo device.
Pointing down is the most common way of getting the best average
ambient illumination level. Pointing up almost never is.


I think you may have skipped too lightly over where I say that the
motion detector unit is designed for 24 hour operation so clearly
the photocell is not for sensing darkness for "night time only"
operation.
Click to expand...
 
"The Natural Philosopher" <A@b.c> wrote in message
news:1114675569.2845.1@spandrell.news.uk.clara.net...
BIG NIGE wrote:

I have to ask why do you say that the photocell cannot be to detect
light or
dark. you say that it is 24 hour operation. All pir operated lights

He never said it was a PIR operated light.

In fact I assumed it was part of an alarm system.
These normally have the photo cell, to allow an _option_ to control a
Click to expand...
light.
I have a couple of controllers of this sort, that feed an alarm, and one
of the configuration options, allows a light to be triggered at night....

Best Wishes

are for
24 hour operation, the pir operates 24 hours, the photocell decides
whether
it switches the light on or not.

"Bill Woods" <woods_b@emercom.com> wrote in message
news:9645F0313AC351D7E@204.153.244.156...

On Tue 26 Apr 2005 21:55:12, R.Lewis wrote:
news:d4m9nj$8ke$1@domitilla.aioe.org

"Bill Woods" <woods_b@emercom.com> wrote in message
news:96447DCF9F01F51D7E@204.153.244.156...

I have a PIR motion detector designed to sense if someone is
walking towards my house.

In addition to a dial for adjusting PIR sensitivity, this
motion detector unit has a photocell mounted to face downwards.
The motion detector unit is designed for 24 hour operation so
clearly the photocell is NOT for sensing darkness for "night
time only" operation.

So what does the photocell do?

Unfortunately I can't test it reliably under light and dark
conditions because it is a wirefree detector unit which
transmits pulses every few seconds and gives very sporadic
responses.

I figure the photocell probably alters the PIR's sensitivity
charactersistics in some way. Is this right?

But would the unit be made more sensitive or less sensitive in
brighter daylight?

The photocell is nothing to do with varying the sensitivity of
the device - it is there to detect 'darkness'.
Commonly these things are arranged so that the pir triggers a
lamp of some for some fixed time, to illuminate a path for
example, but such illumination is not required in daylight.
The position and direction of view the photocell (most
frequently actually either a photo-resistor or a
photo-transistor) depends on the combined optical
characteristics of the housing, lensing, and photo device.
Pointing down is the most common way of getting the best average
ambient illumination level. Pointing up almost never is.


I think you may have skipped too lightly over where I say that the
motion detector unit is designed for 24 hour operation so clearly
the photocell is not for sensing darkness for "night time only"
operation.
Click to expand...
 
Excellent point (I just assumed that it was a light) as most outside
motions are.

Although the photocell is still probably to operate someting else (when its
dark) rather than being an adjustment for the Pir.

"The Natural Philosopher" <A@b.c> wrote in message
news:1114675569.2845.1@spandrell.news.uk.clara.net...
BIG NIGE wrote:

I have to ask why do you say that the photocell cannot be to detect
light or
dark. you say that it is 24 hour operation. All pir operated lights

He never said it was a PIR operated light.

In fact I assumed it was part of an alarm system.


are for
24 hour operation, the pir operates 24 hours, the photocell decides
whether
it switches the light on or not.

"Bill Woods" <woods_b@emercom.com> wrote in message
news:9645F0313AC351D7E@204.153.244.156...

On Tue 26 Apr 2005 21:55:12, R.Lewis wrote:
news:d4m9nj$8ke$1@domitilla.aioe.org

"Bill Woods" <woods_b@emercom.com> wrote in message
news:96447DCF9F01F51D7E@204.153.244.156...

I have a PIR motion detector designed to sense if someone is
walking towards my house.

In addition to a dial for adjusting PIR sensitivity, this
motion detector unit has a photocell mounted to face downwards.
The motion detector unit is designed for 24 hour operation so
clearly the photocell is NOT for sensing darkness for "night
time only" operation.

So what does the photocell do?

Unfortunately I can't test it reliably under light and dark
conditions because it is a wirefree detector unit which
transmits pulses every few seconds and gives very sporadic
responses.

I figure the photocell probably alters the PIR's sensitivity
charactersistics in some way. Is this right?

But would the unit be made more sensitive or less sensitive in
brighter daylight?

The photocell is nothing to do with varying the sensitivity of
the device - it is there to detect 'darkness'.
Commonly these things are arranged so that the pir triggers a
lamp of some for some fixed time, to illuminate a path for
example, but such illumination is not required in daylight.
The position and direction of view the photocell (most
frequently actually either a photo-resistor or a
photo-transistor) depends on the combined optical
characteristics of the housing, lensing, and photo device.
Pointing down is the most common way of getting the best average
ambient illumination level. Pointing up almost never is.


I think you may have skipped too lightly over where I say that the
motion detector unit is designed for 24 hour operation so clearly
the photocell is not for sensing darkness for "night time only"
operation.
Click to expand...
 
Bill Woods wrote:
On Tue 26 Apr 2005 21:55:12, R.Lewis wrote:
news:d4m9nj$8ke$1@domitilla.aioe.org

"Bill Woods" <woods_b@emercom.com> wrote in message
news:96447DCF9F01F51D7E@204.153.244.156...
I have a PIR motion detector designed to sense if someone is
walking towards my house.

In addition to a dial for adjusting PIR sensitivity, this
motion detector unit has a photocell mounted to face downwards.
The motion detector unit is designed for 24 hour operation so
clearly the photocell is NOT for sensing darkness for "night
time only" operation.

So what does the photocell do?

Unfortunately I can't test it reliably under light and dark
conditions because it is a wirefree detector unit which
transmits pulses every few seconds and gives very sporadic
responses.

I figure the photocell probably alters the PIR's sensitivity
charactersistics in some way. Is this right?

But would the unit be made more sensitive or less sensitive in
brighter daylight?

The photocell is nothing to do with varying the sensitivity of
the device - it is there to detect 'darkness'.
Commonly these things are arranged so that the pir triggers a
lamp of some for some fixed time, to illuminate a path for
example, but such illumination is not required in daylight.
The position and direction of view the photocell (most
frequently actually either a photo-resistor or a
photo-transistor) depends on the combined optical
characteristics of the housing, lensing, and photo device.
Pointing down is the most common way of getting the best average
ambient illumination level. Pointing up almost never is.


I think you may have skipped too lightly over where I say that the
motion detector unit is designed for 24 hour operation so clearly
the photocell is not for sensing darkness for "night time only"
operation.
Click to expand...
This sounds like a unit that I have. It can be set for motion activation
and/or darkness. For some strange reason, the manufacturer didn't see
the need to incorporate a daytime inhibit on the motion detector.

--
Paul Hovnanian mailto:paul@Hovnanian.com
------------------------------------------------------------------
SHIFT TO THE LEFT! SHIFT TO THE RIGHT!
POP UP, PUSH DOWN, BYTE, BYTE, BYTE!
 
By operate an alarm I assume that you are referring to some kind of chime
system rather than an Intruder alarm.


"Roger Hamlett" <rogerspamignored@ttelmah.demon.co.uk> wrote in message
news:jw1ce.7370$YF5.1594@newsfe5-win.ntli.net...
"The Natural Philosopher" <A@b.c> wrote in message
news:1114675569.2845.1@spandrell.news.uk.clara.net...
BIG NIGE wrote:

I have to ask why do you say that the photocell cannot be to detect
light or
dark. you say that it is 24 hour operation. All pir operated lights

He never said it was a PIR operated light.

In fact I assumed it was part of an alarm system.
These normally have the photo cell, to allow an _option_ to control a
light.
I have a couple of controllers of this sort, that feed an alarm, and one
of the configuration options, allows a light to be triggered at night....

Best Wishes

are for
24 hour operation, the pir operates 24 hours, the photocell decides
whether
it switches the light on or not.

"Bill Woods" <woods_b@emercom.com> wrote in message
news:9645F0313AC351D7E@204.153.244.156...

On Tue 26 Apr 2005 21:55:12, R.Lewis wrote:
news:d4m9nj$8ke$1@domitilla.aioe.org

"Bill Woods" <woods_b@emercom.com> wrote in message
news:96447DCF9F01F51D7E@204.153.244.156...

I have a PIR motion detector designed to sense if someone is
walking towards my house.

In addition to a dial for adjusting PIR sensitivity, this
motion detector unit has a photocell mounted to face downwards.
The motion detector unit is designed for 24 hour operation so
clearly the photocell is NOT for sensing darkness for "night
time only" operation.

So what does the photocell do?

Unfortunately I can't test it reliably under light and dark
conditions because it is a wirefree detector unit which
transmits pulses every few seconds and gives very sporadic
responses.

I figure the photocell probably alters the PIR's sensitivity
charactersistics in some way. Is this right?

But would the unit be made more sensitive or less sensitive in
brighter daylight?

The photocell is nothing to do with varying the sensitivity of
the device - it is there to detect 'darkness'.
Commonly these things are arranged so that the pir triggers a
lamp of some for some fixed time, to illuminate a path for
example, but such illumination is not required in daylight.
The position and direction of view the photocell (most
frequently actually either a photo-resistor or a
photo-transistor) depends on the combined optical
characteristics of the housing, lensing, and photo device.
Pointing down is the most common way of getting the best average
ambient illumination level. Pointing up almost never is.


I think you may have skipped too lightly over where I say that the
motion detector unit is designed for 24 hour operation so clearly
the photocell is not for sensing darkness for "night time only"
operation.
Click to expand...
 
"Paul Hovnanian P.E." <Paul@Hovnanian.com> wrote in message
news:427296C3.9897659F@Hovnanian.com...
Bill Woods wrote:

On Tue 26 Apr 2005 21:55:12, R.Lewis wrote:
news:d4m9nj$8ke$1@domitilla.aioe.org

"Bill Woods" <woods_b@emercom.com> wrote in message
news:96447DCF9F01F51D7E@204.153.244.156...
I have a PIR motion detector designed to sense if someone is
walking towards my house.

In addition to a dial for adjusting PIR sensitivity, this
motion detector unit has a photocell mounted to face downwards.
The motion detector unit is designed for 24 hour operation so
clearly the photocell is NOT for sensing darkness for "night
time only" operation.

So what does the photocell do?

Unfortunately I can't test it reliably under light and dark
conditions because it is a wirefree detector unit which
transmits pulses every few seconds and gives very sporadic
responses.

I figure the photocell probably alters the PIR's sensitivity
charactersistics in some way. Is this right?

But would the unit be made more sensitive or less sensitive in
brighter daylight?

The photocell is nothing to do with varying the sensitivity of
the device - it is there to detect 'darkness'.
Commonly these things are arranged so that the pir triggers a
lamp of some for some fixed time, to illuminate a path for
example, but such illumination is not required in daylight.
The position and direction of view the photocell (most
frequently actually either a photo-resistor or a
photo-transistor) depends on the combined optical
characteristics of the housing, lensing, and photo device.
Pointing down is the most common way of getting the best average
ambient illumination level. Pointing up almost never is.


I think you may have skipped too lightly over where I say that the
motion detector unit is designed for 24 hour operation so clearly
the photocell is not for sensing darkness for "night time only"
operation.

This sounds like a unit that I have. It can be set for motion activation
and/or darkness. For some strange reason, the manufacturer didn't see
the need to incorporate a daytime inhibit on the motion detector.

--
Paul Hovnanian mailto:paul@Hovnanian.com
Click to expand...
Why would you need a pir that did not detect in the daylight?
You may need a pir that does not turn on a light in daylight hours but why
inhibit the pir function?
 
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