All Pir's Led's Permanently On

[lawandorder]

Hi,

Many thanks to everyone who gave me the benefit of their experience. I have just come back from the house having disconnected the mains and removing the battery and then reconnecting again and lo and behold the LEDS have gone off and are acting as LEDS should do (or LED's on PIR detectors anyway!).

All your replies were very gratefully received.

Rgds

Neilo

Glad you got this problem sorted but it would be interesting to know why it happened in the first place.

My guess (and it is only a guess) is that the existing PIRs had the option to be wired as latching and that at some time during your initial repair the voltage to them dropped to a level where the latch initiated. (perhaps during battery test?).

As I say, just a guess but it does seem strange that they all "appeared" to latch.

[Neilo]

I think you might be right about the latching. To be honest I changed the detector on the 'faulty zone' without powering off etc. (hence the expression a little bit of knowledge is a dangerous thing!) . It would seem, that thanks to your help and the rest of the replies, I probably got away with it but I'll know to switch everything off next time.

Once again many thanks. No longer in a hole I'd dug!

[mark auto]

sorry for being a dumbass guys, but could someone explain latching to me? i dont get it

[lawandorder]

I think you might be right about the latching. To be honest I changed the detector on the 'faulty zone' without powering off etc. (hence the expression a little bit of knowledge is a dangerous thing!) . It would seem, that thanks to your help and the rest of the replies, I probably got away with it but I'll know to switch everything off next time.

Once again many thanks. No longer in a hole I'd dug!

BS4737 demanded that there was a way of identifying which electronic detector had triggered so in the event of a false alarm the problem could be recified.

Nowadays that usually means fitting a control unit with multiple zones and each detector tends to be wired to it's own zone and when the alarm activates the user can see which zone triggered.

In the good old days before you could buy an 8 zone panel for less than the cost of a round of drinks many panels were single zone.

To identify which detector had triggered an extra wire was used in each detector which was connected to the latching terminal. As I recall this wire went positive when the system was set and the walk test LED would stay illuminated until manually reset.

Many panels still have an output for latching detectors and latching still has it's uses with things like vibration detectors etc.

Some detectors even had a remote output to allow an additional walk test/latch indication to be mounted near the panel.

If you work for any of the long established nationals you may still come across this type of installation.