Re: Strain gauge

[Robert L Bass <sales@xxxxxxxxxxxxxxxxxxxxx>]

> The Pulsors I have at least claim to vary their resistance depending on
> stress.  > The delta detection appears to occur in the processors which
> adapt to the new value with a relatively short time constant.

Thanks, Dan, you're right.  They don't generate a current as I
erroneously stated.

> It might be possible to do something over a longer period if you
> could factor out various non-occupancy-related noise, though
> thermal changes in the structure to which the Pulsor is attached
> could be a big problem...

There's more to it than that.  The resistance change is momentary
and occurs when the joist flexes.  It returns to its previous
state once the joist stops moving.  In short, they detect a
moving load on the floor above.  They do not report the existence
of a static load.

> Given the phenomenal signal processing power that you can
> throw at a problem for relatively low cost these days (even
> compared to a few years ago) it may be worth looking at.

I wouldn't discourage anyone from researching possible solutions
to the problem of occupancy sensing.  However, before starting it
helps to understand the limitations of the sensors themselves.
These devices detect joist movement.  A small kerf is cut into
the joist and the detector is cemented in place under that cut.
When the joist flexes the detector is stretched, causing a
momentary electrical change.  It's not like a pressure switch
that closes when you stand on it and opens when you leave.

Also note that the sensors can't tell in which direction a load
is moving -- into or out of an area.  They only know that a load
has been placed upon the floor somewhere within a certain radius.
TTBOMK, the transducers don't differentiate between "load placed"
and "load removed."

> | I've used these sensors on my own jobs a few times.  When
> | properly installed they work well.  Poorly installed they won't
> | detect anything smaller than Mama Kass.
>
> I installed one in my house to see how well they worked (very well) and
> then gave several to a friend.  They are great for houses with cats (and
> presumably other pets).  I bought a bunch more but never got around to
> installing them.  Now the epoxy is way out of date. :(
>
> | If you want to experiment with one of these sensors let me know.
> | Although I don't currently list them online, I carry Sure
> | Action's other lines and can provide these as well.
>
> Do you happen to know whether they sell replacement epoxy packs or
> specify a brand/type that is suitable?  (See my complaints about
> current hardware store epoxy elsewhere...)

Almost any two-part epoxy cement should do the job.  As long as
the cement is rigid -- not flexible stuff like RTV -- it should
work fine.  If you want I'll call and ask them to send you a
package to experiment with.  It's been a while since I spoke to
them but the rep seemed pretty decent -- likes DIYers.  :^)

--

Regards,
Robert L Bass

Bass Burglar Alarms
The Online DIY Store
http://www.BassBurglarAlarms.com

--

Never underestimate the power of very stupid people in large
groups.