Desensing PIR Detectors

Jun 06, 2017 10 Replies

Hi all,



Is there a way to make PIR motion sensors a bit *less* sensitive? I have one of these Driveway Alert ones from CPC and it's supposed to have a range of about 30' but is actually detecting vehicles crossing in front of it at closer to 60' which is generating a lot of false alerts. I was thinking maybe some kind of coloured film that could be stuck over the sensor, perhaps? Sigh. It's very windy today and that seems to be setting it off too. :(



Chris


Angle it down a bit, so that it doesn't see the distant traffic. As to the wind setting it off, shrubs waving in the wind is enough to trigger a PIR sensor.

I have a thermal camera for work. It sees through black bin-liners but not without some attenuation, so I'd start there.

Cheers

Try some filters using polythene from a _thick_ polythene bag. You might have to stack a few layers.

Brian

I've just this minute bought this selection:

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With a bit of luck, just *one* of these should have the desired effect. I just need to try them all one after the other.

The backing would likely interefere with tests. I'd go with a bag.

NT

I wasn't going to leave the backing on! I'll peel it off and attach each one to some clingfilm for testing purposes.

do you not have binbags where you are?

NT

The thing is thes devices are not linear, they actually are all or nothing based on a threshold. As they are not actually focussed as such it can be very hard to change them. Most of the ones I've seen have a little internal adjustment for it. However as you have discovered they tend to be far more sensitive than they should be. In the end, angling it down and making sure nothing in the region can move in the wind is the only way. I gave up in the end. Nowadays I don't need a device like this, but my original use was to detect me when I was close to my gate and bleep so I could find it. Brian

Wouldn't look very elegant, would it!

A piece of bag polythene fixed flat onto the lens element would, assuming it's done neatly, be neat. It would just look black or whatever colour the bag was instead of clear, as does fablon of course. But do we need to state the obvious?

NT

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