"ehsjr" wrote in message
news:3qihj.3848$K%6.3695@trndny04...
Joerg wrote:
ehsjr wrote:

You call that a coil? That's not a coil.
*This* is a coil!


No, it's a petunia. Or whatever. (I am not a botanical expert)

So, what's that super-stretch edition of coil for?


For a permeability tuned oscillator. It's an experiment to
measure water level, which changes only 3 feet nominal at
the site.

The finished coil is 42" of wire on 46" of PVC. A float
makes the coil ride up and down on a galvanized rod as
the water level changes.

It is accurate to within an inch, with +/- 3" being acceptable,
so that part is good. There is a big (ie 3" change in reading
with a 30F change in ambient) temperature problem to be solved,
but I ran out of warm weather to work on it. Looking for +/- 3"
accuracy between 50 and 100 F.

Ed

Where do you think the temperature effect is coming in - the oscillator
portion or the coil?
Some freeze spray is usually a good way to find gross effects of
temperature.

Does the inductance change also with temperature? An inductance bridge would
be helpful here.

How about using a LVDT approach instead?