Re: Help with 7 Circuit Project?

["Robert L Bass" <robertlbass@xxxxxxxxxxx>]

>> ...When thunder triggers glass breaks it usually trips several of them.
>
> Don't know about you, but the glass breaks I use don't get tripped from
> thunder.  Edmonton (Alberta) is also the "thunder & lightning" capital of
> the Prairies.

Ordinarily I ignore this poster due to his abusive behavior but the above
needs to be answered for the benefit of other readers.  First of all, Mr.
Olson is not an installer nor even an experienced DIYer.  Second, he resides
in Vancouver, BC -- rather a long commute from Edmonton, Alberta.  Third,
there is NO acoustic glass break on the market that doesn't occasionally
false from thunder.  I've been installing glass break detectors for more
than 20 years and I can assure the readers Mr. Olson is dead wrong.

>> Have the glass break zones start a timer.
>
> Zone "anding", timers...
> --- snip snide comments intended to incite flames ---

Zone ANDing is one of the requirements of the current SIA standard for false
alarm reduction.  I suspect the gentleman on the standards committee would
disagree with Mr. Olson as do I.  However, the concept I explained in this
thread could more accurately be called zone "NANDing" since it requires that
one and only one acoustic glass break within a given group of detectors (say
for example, all those facing the same direction) be triggered to generate
an alarm.

>> If any glass break zone is tripped wait 10 seconds
>> before triggering an alarm.  If a second glass break
>> activates within that time frame, take no action.
>
> And I suppose these glass breaks are in different
> rooms...

Acoustic glass breaks can typically cover up to 50' (25' radius) so yes,
they are usually installed in separate rooms.  If you had actually installed
any of them you would know that.

> with windows facing in different directions...

That is not essential but it can actually work to one's advantage using this
technique.  When windows in more than one room face the same direction, my
method is enhanced because thunder will be more likely to trip several zones
at once.  Since most homes have more than one room on each side, that is
usually the case.

> Good plan...  But what if they're not??  What if the room is large enough
> to require two glass
> breaks??

If the room is longer than 50 feet on a side it might need two glass breaks.
In that case, a simple modification to the rule will allow one to "OR" the
two glass break zones within that room.

> What if the perp smashes a window that's close
> to or actually in an area where the coverage patterns happen to overlap??

Quality acoustic glass breaks properly installed will not respond to
breakage in an adjacent room.  It is extremely rare to need more than one in
a single room.  However, if two or more were in a single room they can be
zone ORed using a simple mod to the rule.

> So he smashes the glass and continues to break the broken bits out of the
> frame.

That's another misconception about glass breaks borne of inexperience.  The
good ones generally don't respond to secondary breakage once the window has
been smashed.  That has to do with the design of the glass break detector.
Once the "skin" of the room has been broken, the additional noise generated
by clearing the shards won't include sufficient low frequency sound to
generate a secondary trip.  Granted, if someone wanted to install the old
Sentrol "ShatterBox" units or IEI junk from the 70's, that would be a
problem.  But those falsed when nothing at all was happening.

--

Regards,
Robert L Bass

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