Unusual PIR requirement.

RossR · 19 Jan 2011

Hi all,

Strictly speaking this shouldn't be in the alarm forum, but I figured it was the best place for it.

I'm looking for a PIR to use as an occupancy sensor. It doesn't need to switch any significant load however - it'll be feeding into some home automation electronics. So the main requirement is fast triggering. i.e. short time between entering a room and it sending a signal. It doesn't matter if it gives an occasional false trigger. I guess this means I need a pulse count setting of 1? Some adjustment of the coverage direction would be good. It doesn't have to be super cheap, but obviously I'd rather not spend money I don't have to.

Any recommendations?

Thanks,

Ross

Geps · 19 Jan 2011

There are normally PIR modules for whichever network you're planning on using (I'm looking at Idratek).

RossR · 19 Jan 2011

In the spirit of DIY I'm building a custom system. I just need a normally open or closed contact on the output.

I was hoping for considerably less than £60 each too!

Geps · 19 Jan 2011

There are plenty of ceiling mount PIRs used for lights.

Just get one of those and connect it up accordingly.

mints73 · 19 Jan 2011

If you require a very qick pir and very good false alarm rejection look at

Honeywell IS215T around £8 I have used lots on bells only and remote signalling systems over a few years with no troubles.

Of course they are made in China but what is not ?

RossR · 19 Jan 2011

Those tend to be mains powered and have long timers on them from what I've seen. I'm just after a standard alarm style PIR but that is quite sensitive.

Alarm · 19 Jan 2011

Any standard PIR wil do this.
NC going Open.
A DT will stop false activations or even use a Quad PIR.
http://www.securitywarehouse.co.uk/catalog/index.php?main_page=product_info&products_id=1676

This is good. see above.

RossR · 20 Jan 2011

Thanks for the various replies. However I don't think I made myself clear with requirements.

With PIRs there is a trade off between speed of detection and false alarms. Normally the important thing is low false alarm rate. This is achieved by requiring multiple pulses before a signal is sent, and in some cases dual technology sensors. Both of these slow the detection down though. Normally it doesn't matter if it takes a couple of seconds before a person is detected.

In this application, I don't care about false alarm rate. I do care about speed of detection. I want a person to be detected within the first meter of them entering.

mints73's suggestion might be suitable - I like the look-down zones. I can't find any information on it's pulse count settings though.

bernardgreen · 20 Jan 2011

RossR said:
I want a person to be detected within the first meter of them entering.

Beams across the entry points will provide that for you. Depending on the processing power available a pair of beams (side be side) will enable you to determine whether they are entering or exiting the area.

Such a system was used for many years to count how many people were in a room that had maximum occupancy restrictions. It used a simple micro-processor and was seldom wrong as to how many people were in the room.

mints73 · 20 Jan 2011

RossR said:
Thanks for the various replies. However I don't think I made myself clear with requirements.

With PIRs there is a trade off between speed of detection and false alarms. Normally the important thing is low false alarm rate. This is achieved by requiring multiple pulses before a signal is sent, and in some cases dual technology sensors. Both of these slow the detection down though. Normally it doesn't matter if it takes a couple of seconds before a person is detected.

In this application, I don't care about false alarm rate. I do care about speed of detection. I want a person to be detected within the first meter of them entering.

mints73's suggestion might be suitable - I like the look-down zones. I can't find any information on it's pulse count settings though.

The Honeywell has pulse count adjustment, on its fastest setting it is very very quick I cannot think of another any faster and the price is low enough
for you to buy one and see if it will do.

Alarm · 20 Jan 2011

RossR said:
Thanks for the various replies. However I don't think I made myself clear with requirements.

With PIRs there is a trade off between speed of detection and false alarms. Normally the important thing is low false alarm rate. This is achieved by requiring multiple pulses before a signal is sent, and in some cases dual technology sensors. Both of these slow the detection down though. Normally it doesn't matter if it takes a couple of seconds before a person is detected.

In this application, I don't care about false alarm rate. I do care about speed of detection. I want a person to be detected within the first meter of them entering.

mints73's suggestion might be suitable - I like the look-down zones. I can't find any information on it's pulse count settings though.

Wrong so wrong. Most if not all detectors have look down zones, its called creep protection. Pulse counts can be deselected. Any PIR can "grab" in an instant. As also suggested beams across the entry point.Might not be suitable for your app though.

Buy a 7 quid one see how it goes, you might be suprised as its not for security.

Europlex · 20 Jan 2011

Fit a ' CURTAIN ' PiR

Alarm · 20 Jan 2011

Indeed, a Curtain Pir.
Well done, should have thought of that myself.
Ahh well no one is perfect.

Still top bananna for that.

Europlex · 20 Jan 2011

Even fitting one in a horizontal plane can work well in some situations, just needs some thought.

Alarm · 20 Jan 2011

Box, out thinking.

Exactly.

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