Grandfather ( clock ) triggers alarm

[bernardgreen]

The swinging pendulum of a restored grandfather clock seems to be the culprit that has triggered a couple of false alarms. The clock was stopped and no more triggers. Being looked into in more detail on Tuesday.

Anyone have any experience of similar trigger sources

 

[Europlex]

Forgive me laughing Bernard, but, I'll go with it.

Adj the angle of cover from the detector by a minute amount, that should do it.

Still not sure I believe it though.


What on earth are we doing up at this time on a Sunday morning reading/answering Forums?

Must be an age thing, I'll not see the BIG *0 any more

 

[bernardgreen]

I did laugh when I was told about it. It is a brass disc pendulum so could be reflecting IR energy with enough movment to trip a PIR.

Why am I up this early ? Bright sunlight shining into the bedroom ( I hate closed curtains ).

Age does come into it. I reluctantly accept my OA pension ( helps fund the restoration of this cottage ) but refused the bus pass as I feel far too young to be old enough for a bus pass. Queueing up for a bus is a waste of time.

 

[bernardgreen]

Update

The owner tells me tests were carried out with a PIR pyro element connected to oscilloscope. A weak signal in synch with the swing of the pendulum could be seen. It increased when a person stood still in the room. It ceased when the pendulum was stopped.

So it seems the pendulum is reflecting enough IR energy to create an output from the pyro sensor. During the tests this signal was not enough to trigger the PIR of the alarm.

It is assumed that when the alarm was triggered there was a stronger source of IR for the pendulum to reflect. As yet no idea what that source was.

 

[EightyTwo]

Isn't there usually glass in front of the pendulum? I was led to believe that glass was opaque to IR and so the PIR shouldn't be able to see through it. Maybe the application of some kind of window film (solar film) would sort this out without looking too bad. Not really an option if it's antique, though!

Alternatively, mask out the fresnel lenses that are 'looking' at the pendulum...

 

[bernardgreen]

Eighty Two

Glass is not totally opague to IR and the opacity varies from type to type as in infra red lamps which are almost translucent to IR

I will be getting more info about this soon as I now have an address for the person who carried out the tests on Tuesday.

 

[sparkymarka]

First thing what make and model was the pir ?

 

[bernardgreen]

The PIR in the alarm system is a Securis Model D20

The sun would have been shining into the room at the time the sensor tripped but not onto the clock or the sensor.

It is assumed the moving pendulum was reflecting IR energy radiating from an area of the wall warmed by the incoming sunlight.

The fix is to replace the sensor with a dual tech.

 

[sparkymarka]

only thing I would say Bernard the securis pirs where a load of cr*p and stem from the late eighties early nineties they had loads of pre- cutouts on the rear of the case ( spider heaven ) and not very good at all. replace with an rx40 as we moved onto the optex pir after the securis and never looked back.

 

[EightyTwo]

I know that glass is transparant to microwaves!! A dualtech may not help. We like the Optex RX40's too... amongst other things, they have quad optics.

 

[Europlex]

rx40

Don't forget they are out of production now, d*** shame, very good little detector.

 

[sparkymarka]

Well so they say ! but you can still buy dx40 from optex replaced by the optimal now replaced by the cdx ......still think it will be a couple of years until
The rx 40 is out of stock....

 

[bernardgreen]

Final update.

The alarm technician installed a new sensor yesterday, He made a point of being there at the same time that the the alarm had previously been false triggered to see if there was anything unique at that time.

The grandfather clock may not be the culprit even though the PIR element was responding to the movement of its pendulum with a very small but discernable analogue signal when there was reflected sunlight on the pendulum.

South facing window, clock standing one side of the window and the sensor in the corner on the other side. Bright sunlight reflected by a glass coffee table illuminates a trophy cabinet on the north wall. The trophies reflect the light making a dappled pattern on the south wall around the sensor. Moving the curtains affect the pattern and while it did not trigger the new sensor ( dual tech ) It did register on the test sensor but less than a quarter signal needed to trigger the sensor. So it seems the curtains moving and bright sunlight were the culprits. ( the top vent window was open at the time so the breeze would have moved the curtains. )

 

[EightyTwo]

And the lessons are..?

1. Don't use a 'scope on a PIR to find the false alarm (it could lead you up the garden path).

2. Replace dodgy old PIRs when they false alarm.

3. Close your windows when you set your alarm.

4. Believe sparkymarka...

5.... Did I miss anything? Lol

 

[bernardgreen]

Did I miss anything? Lol

Yes you did.

Don't boast with a cabinet full of trophies.......