"Ben Okopnik" wrote:

> Lew, that's an interesting statement. What's unreliable about a
> well-designed float (e.g., http://x.co/KGoQ), or for that matter, 
> the
> cycling pump that we were talking about?
-------------------------------------
Everything.

Float switches define the baseline of a failed application.

I make a living replacing failed float switches in the industrial 
market.

You can find similar stories of failure in the recreational marine 
market.

A "Rule" brand product comes to mind.

They jam with crud or residual build up or short out.
---------------------------------
> These seem like no-brainers.
------------------------------
That is exactly what they are.
-----------------------------
> It's not like you're working with high-viscosity materials here; 
> it's
> pretty well limited to water with maybe some oil and fuel mixed in.
> What's the catch?
----------------------------
Gunk.
------------------------------

> OK, I can see conductivity as being of marginal use if the contacts 
> get
> coated with oil; somewhat of a ditto for capacitance, although for
> slightly different reasons. What's the failure mode for ultrasonic 
> or
> pulse radar?
-------------------------------
Continuous ultrasonic suffers from gunk build up and/or foam, same 
with ultrasonic point level (gap switch) technology.

These days the US Navy is big on pulse radar at $2K-$3K each, not to 
mention size and power consumption.

Not much opportunity in the recreational marine market at those 
levels<G>.

Bottom line, of the 10-12 level measuring technologies available, none 
can provide a reliable solution at a price, physical size, and power 
consumption the market can support.

Lew

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