Re: Snow load evaluation

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"Dan Lanciani" <ddl@danlan.*com> wrote in message
news:1338519@xxxxxxxxxxxxxxxxxxxxxx
> In article <EbGdnXAxJfEx0VLYnZ2dnUVZ_qGjnZ2d@xxxxxxx>,
ROBERT_GREEN1963@xxxxxxxxx (Robert Green) writes:
> | Anybody doing anything automated in terms of detecting an excessive snow
> | load on a structure's roof?   I saw a news report about upstate NY where
a
> | guy said "when your doors begin to stick, that's when it's time to clear
the
> | snow off the roof.  It's good to know one of the warning signs but
surely
> | there's got to be a better way!
>
> For something like this (and for the recently mentioned "static" occupancy
> detection) I would recommend looking into Sure Action's Pulsors with
> something *other* than their standard fast-change-detecting zone
processors.

Either I'm having a deja vu, or we've been over this before but with
basement joists.  I went to their site:

http://www.sureaction.com/

and they've got an interesting lineup.  I didn't realize how finely they
could be calibrated.  They offer a good solution to pet problems, although
they still can't distinquish between a small child and large dog, I fear.  I
might have to get some just to play with although they're a little pricey.
I was actually hoping one of our resident McGyver's could outline how to
make a deflection sensor out of $7 laser pointer and an X-10 Hawkeye.   Seem
to me the key is in the epoxy they use to hold the sensors down.  (-:

If I could shoot a laser at a mirror mounted on a basement joist center from
the end of the joist and reflect it back to a sensor with a narrow slit, it
should be able to detect very slight deflections.  Might even be able to
acquire some preliminary data by shining said beam on a piece of paper and
photographing the paper using a *very* long exposure and high f-stop.  The
laser beam should draw a pattern on the paper showing the nature and extent
of the deviations caused by motion on the main floor.

If it turns out I can reliably detect motion on the floor above with that
test, I might consider looking at roof issues.  If snowloading can make
doors stick, it should cause a noticeable deflection in a properly aligned
laser beam long before that happens. My problem is that getting to the roof
rafters is a lot harder than accessing the basement joists.

--
Bobby G.