How well do Active IR Sensors cope with Power Outages?

[Geflugenmitt]

Hi, I have a wireless (433MHz) alarm system. The PIR sensors this came with are prone to false triggering.

The alarm manufacturer does not supply any active IR sensors that are compatible, however I do have the technical know-how to buy an active transmitter/receiver pair and link it to a spare wireless sender, thus triggering an alarm. I am aware that the active setup requires a permanent power source - I can sort that via a mains adaptor.

I am wondering what might happen though if the mains power failed. In the milliseconds before it died completely, I would need the active IR device to intelligently realise that the reason it wasn't seeing a beam any more was because the power has just gone off, and not because the beam has been broken by an intruder. I would need it to maintain a 'Normally Closed' output condition throughout, up to and including when the power came back on again.

I am capable of designing a circuit that would sense a power fail and kill the power to the wireless sender first, so if the IR detector then went open cct it wouldn't matter because the alarm signal would never get transmitted to the control box. But that would be a whole extra level of complexity.

Also, is anyone aware of an active IR sender/receiver in a single box that you use with a corresonding mirror? Otherwise I need power going to two boxes - sender and receiver.

Thank you.

 

[sparkymarka]

That's what battery back up is for ! Try using a power supply with battery back up!

 

[EightyTwo]

Do you really need an IR beam detector? It might be better to go with a dual tech and wire it's output to the wireless sender. As sparkymarka says, use a battery backed psu. You could also consider running the sender from the same psu - just knock up a linear (not switching) voltage regulator than will knock the psu's 13.8V output down to the battery voltage of the sender.

There are battery operated beams available. Optex and Takex (was Pulnix) make loads of them but they are really designed for perimeter protection (and you don't want to know how much the lithium 'D' cells cost..!). Takex also make one called a PR-11B which is the reflector type but it's not battery powered.

There's another company whose products we've used but I'm damned if I can remember what they're called!

 

[bernardgreen]

Also, is anyone aware of an active IR sender/receiver in a single box that you use with a corresonding mirror? Otherwise I need power going to two boxes - sender and receiver.

That method requires the system to be able to distinguish between reflections from the mirror and reflections from people breaking the beam. This makes a reliable combined TX+RX module much more expensive than a system using separate TX and RX modules.