PIRs

There are many different types of PIS on the market.  For home automation we tend to use two or three types.  The most common and easily available PIRs are those found in security systems.  These are very good for applications where lights are to be switched on (or 'DWELLed on', for example hallways and external lights.

Here's the connection diagram:
 

PIRs for OFF Applications 

 Experience has taught us that security PIRs are not particulary good for applications where a lack of movement should switch off lights etc.

This is because security PIRs are designed to reject false-positives, for example thermals or pet movement.

If you have an application for say switching off kitchen lights on 'no occupancy' its better to use hyper sensitive PIRs. You can get these in small discrete packages with TTL output that is directly compatible with WebBrick Digital inputs.

See Farnell part number 1373718 as an example

Would you also suggest that with ceiling pir's of this nature that atleast 2 be installed in a normal sized room due to the 50deg scope?

Or place them in the corner and loose 1/2 of the detection zones?

I would say run the wire so you have the ability to add another one, but not necessarily put it in straight away.

The less stuff visible the better imo.

Ian

For clarity, the application you are think of is the 'Off' application.

I have a room that has two 'hyper sensitive' sensors.  One is as 45deg looking into the room in both the vertical and horizontal plane.  This has proved 100% reliable for the area (a kitchen separated by a large island).  Even a small hand movement will register.

The second is pointing straight down by the entrance door way and occaisonally doesn't detect movement over a 10 min period.

In open rooms less than 10m one PIR will be fine providing it is 'sighting' well.

 I'll be moving mine at some point!

Regards

Andy
 

I spoke to an alarms guy who is trying to convince me to stick with alarm cable for PIRs - he sees them as less hassle than cat5...... appreciate your views on this please.

I certainly am interested in the prospect of programming a task on motion sensor - eg lighting on - but bigger scale stuff like dialout on alarm automation could be achieved via conventional alarm panel..... so is cat5 the recommended route? Or alarm cable better?

tx

 Ravi

 - in performance terms there is no comparision of CAT5E versus security cable.  The CAT5E is good for for 1GB and 10GB on the short hauls found in homes.

 CAT5E is fullt re-purposeable - i.e. you want an IP camera in place of a PIR - you got it!.  With the extra cores you *could* do ethernet and a PIR on the same cable.

 The only hassle I can see is colour schemes, security cable uses solid colourw whereas CAT5E uses pair colours.  There is a very slight difference in thickness.

 When I had my alarms implemented, it was a mere case of a pot of tea to decide on the colours.  The longer debate related to both the automation system AND the alarm system seeing the PIRs - this they were less keen on.  We ended up with some PIRs being security only, and the home automation set being grouped in to upstairs and downstairs then taken to a separate input on the alarm panel.

 This is so that at maintenance they can discriminate bewteen PIRs they need to maintain and check, and those that they leave along.

 The security market is quite tied up in NACOSS, but these are recommendations that effectively become 'regulations' through the demand of insurance companies.  You also need to understand that many security installers are trained for a set group of panels and accesories and wish to keep exclusively to those.  This is because they have to maintain the equipement.

 The debate has been exercised many times, at the top end of the market there is a divergence with security systems being implemented on the same hardware as home automation and the maintenance contracts covering both.  Some installers are NACOSS registered, and its their seal of approval that satisfies the insurance company.

 These days (oddly enough) it is sometimes better to have a security alarm but not declare it to your insurance company.  This is because you may find that you're not covered if you are burgled when your alarm is off.  The small increase in premium may be worth the extra cover, particularly if you know your family will not be rigorous in setting the alarm.

 
Andy
 

Another way potential way round the problem of Nacoss installer retiscence:

Many alarm panels have sets of configurable and/or hard wired dry outputs - these can often be used to echo the inputs and so may be used as a feedthrough the alarm panel from the PIR to your brick - keeps the alarm installer happy as he is only implementing standard features and his cable monkies don't get confused by a 'new' cable type :-)

Simon