Re: Strain gauge

[ddl@danlan.*com (Dan Lanciani)]

In article <l6c9v1pgf138726jtfrpivhse6e8qtkbdc@xxxxxxx>, sales@xxxxxxxxxxxxxxxxxxxxx (Robert L Bass) writes:
| > Has anyone here ever mounted strain gauges on
| > basement jacking posts to measure the load changes
| > of the floor supported by the posts?
|
| I imagine someone has though I haven't.  Coincidentally, there
| are strain sensors that measure floor joist flexing to detect
| burglars.  A company called Sure Action makes them.  They call
| the products "Pulsors".  They give off a tiny electrical current
| when the joist flexes due to an intruder's weight above.
|
| You could measure the current and build a simple circuit to
| detect occupancy  but it only responds to flexing -- not a static
| load -- so it still doesn't solve the perennial problem of room
| occupancy for HA.  :(

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.  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.  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'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  Now the epoxy is way out of date.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...)

				Dan Lanciani
				ddl@danlan.*com