Re: Glass skylights

["Russ Brill" <russwbrill@xxxxxxxxxxxxx>]

Don't forget about the heat that's present above a drop ceiling, it will
reduce the range of most PIR's......... Regards, Russ

"Jim" <alarminex@xxxxxxx> wrote in message
news:1118549255.222436.134250@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>
>
> mikey wrote:
> > Curtain PIR?
> >
>
> I had an experience many years ago with using a curtain PIR in a
> similar type of installation.
>
> Customer wanted protection above his drop ceiling against someone
> coming in through the roof. The distance between the hard ceiling and
> the drop ceiling was about 3 feet. I mounted a Visonic (forget the
> model #) curtain PIR on it's side. I seem to remember it was rated at
> 35 feet(?). I couldn't get detection at any range further than about
> 17-18 feet. I wound up having to use more than one unit above the
> ceiling, to cover the area that I wanted.
>
> I had to assume that the divergence of the array, between the two
> ceilings, got too wide with distance to be able to detect the cross
> section of a body perpendicular to the curtain, at anything further
> than 17 feet.
>
> When I tested the unit below the ceiling it worked at a greater
> distance but not at the maximum distance the unit was rated for. I
> found that when the unit was mounted on it's side and you "stood up"
> perpendicular to the curtain, the unit wouldn't detect as far away as
> it would as if the unit were mounted with the unit mounted properly and
> you walked through the curtain in parallel with the array. I assumed
> that since the size of the heat source the unit sees is smaller when
> mounted on it's side, that the range was somewhat shortened.
>
> That was with Visonics very first curtain unit. I'm sure things have
> changed since then. ( don't have much call for curtain units) But it
> would be an interesting experiment to see if it still affects the range
> when used horizontally.
>