alarm PIR

[Steve]

Would raindrops falling from a leaky ceiling 15 foot away be enough to trigger a microwave/PIR detector?

 

[securespark]

Wouldn't think so, but......

 

[bernardgreen]

Would raindrops falling from a leaky ceiling 15 foot away be enough to trigger a microwave/PIR detector?

Micro-wave possibly yes

PIR would need a moving infra red source.

Warm to hot water dripping has been known to trigger a PIR.

Cold water drops wouldn't unless there is also a heat source to illuminate the falling droplets.

Is there a sound detector in the system ? The sound of the drops could be triggering that.

Bernard
Sharnbrook

 

[breezer]

yes it would

the microwave no doubt, since that is how they see people (being 80% water)

the pir although looking for the movement of infra red heat can not see the water as such, but as it obscures it, then it "sees" where the water was, that will cause it to activate.

it should also be noted that 90% of duel technology detectors rely on the microwave not seeing something, so they can economise on the quality of the pir

the other thing is , if there was nothing else "unusual" in the room why else did it go off?

 

[ebee]

go off?
Do you mean activate.
Seriously, running water can trigger microwaves though but I would expect it to have to be closer than that.

 

[Steve]

Hmm. Interesting one. No sound detectors (theres a massive fridge compressor unit 20 feet in the other direction). There is a PIR/microwave detector at the top of the stairs, pointing down the stairs. There is a leak on the 5th step down. One member of staff put a bucket there just before we locked up. There is another leak on the half-landing (6-8 steps lower).

The detector says ADT on it. It flashes red, orange and green in the same LED space. When I stand still, the orange light pretty much stays on (with the other 2 flashing occasionally). If I hide round the corner, the orange light eventually goes off. I take it that whatever triggers the orange light is more sensitive than the other 2?

 

[breezer]

Red means alarm condition

Green pir operated

Orange microwave opeated

 

[Steve]

Red means alarm condition

Green pir operated

Orange microwave opeated

so both have to be operated in order to trigger the alarm? Or have I got that wrong?

 

[RF Lighting]

Yep it is a dual technology detector, so it works by housing two different types of detector in the same unit, and these both need to be triggered at the same time to create an alarm condition, to reduce incidences of false alarms.

 

[breezer]

you do have that right, both must "see" something before an alsrm condition is generated.

That is why it is called a duel tech (duel technology)

the idea is that two detectors of differnt technology will prevent false alarms, so manufacturers have tried various combinations and the best is the pir / microwave.

as police polices have become more strict most (not all) companies fit them as standard

 

[Steve]

the idea is that two detectors of differnt technology will prevent false alarms, so manufacturers have tried various combinations and the best is the pir / microwave.

Hehe. You'd think so wouldn't you?

 

[bernardgreen]

Hmm. Interesting one. No sound detectors (theres a massive fridge compressor unit 20 feet in the other direction). ?

Any moving parts on the compressor, like a fan on the heat exchanger, that would trigger the micro-wave while the moving heated air from the heat exchanger triggers the PIR device ?.

If the sensor is very sensitive an exposed compressor motor on rubber mounts may move enough at start and stop to trigger both micro-wave and PIR sensors.

Fridge = food ?

No chance of rodents when the place is closed is there ?


Bernard
Sharnbook

 

[ebee]

Don`t lose sight of (Like many do) that, in a hostile enviroment, one technology (say Infra Red) might actually be in alarm much of the time.
Therefore you would have a nearly equivalent detector of the other (say microwave) techology detector.
Thus defeating your objective

 

[Steve]

Any moving parts on the compressor, like a fan on the heat exchanger, that would trigger the micro-wave while the moving heated air from the heat exchanger triggers the PIR device ?.

If the sensor is very sensitive an exposed compressor motor on rubber mounts may move enough at start and stop to trigger both micro-wave and PIR sensors.

No chance of rodents. Poison bait everywhere.

I think we are getting somewhere here now. The compressor - it used to run constantly, only shutting down during defrost mode. However, the fridge it drives was re-gassed last week and it cycles a lot more now. It has about 20 mins on, 10 mins off. When it shuts off, it does shudder quite violently, and I wont go anywhere near it when its off, because when it comes back on, it makes a loud bang, and must shudder then too. There are 2 large fans on its evaporator coils, behind the compressor, that blow hot air into the room, past the compressor. To counteract this, there are 2 turbo extractor fans on the opposite wall to cool the room. So the temperature can vary quite rapidly.

Picture of said compressor, we all like pictures
<clicky>
All those pipes shudder during startup and shutdown. And I know the electrics leave a lot to be desired - we're forever banging rollcages into the trunking, so its lid fell off. The sensor is mounted on the opposite wall, pointing 45 degrees to this.

 

[bernardgreen]

If it is the compressor then you may get away with a "shadow mask" made out of metal to screen the sensor from having direct view of the compressor. But in a small room there may be enough refected micro-wave to "see" the shuddering compressor

Have you thought of a through beam sensor system across entry, exit and weak points ? A bit more trouble to install and require a bit of care that nothing has been left blocking a beam when you lock up and set the alarm. A lamp can be fitted in the room to show "beam intact" if it becomes a problem.