[aprssig] FEMA- Flood gauges (feedback)

Robert Bruninga bruninga at usna.edu
Thu Sep 15 16:52:59 CDT 2016

The indicated float switch is completely sealed and has an internal magnetic
reed switch.  As long as the float moves, it will work.  But I guess you are
suggesting the sliding surface on which it slides could become fouled...

-----Original Message-----
From: aprssig [mailto:aprssig-bounces at tapr.org] On Behalf Of Ross Whenmouth
Sent: Thursday, September 15, 2016 5:25 PM
To: Kirby; aprssig at tapr.org
Subject: Re: [aprssig] FEMA- Flood gauges (feedback)

Hi Kirby,

> What happens when gunk grows on the wire? Granted gunk will interfere
> with the float switch, but I would think it would be more likely to
> fail on. I would think failing on would be preferable to failing off.
Gunk on the insulated ribbon conductor will either have a higher dielectric
constant than air (if dry) or be electrically conductive (if
wet) and both cases will tend to "fail on" (indicate a higher water level
than is actually present) as the capacitance between the conductors will be
increased by the gunk.

A pair of insulated rods spaced apart from each other (no plastic webbing
between them unlike with 300 ohm ribbon) or a single insulated rod located
co-axially inside a metallic (or otherwise electrically
conductive) tube would probably be less prone to mis-operation due to
fouling, but would probably cost more to manufacture.

Ross Whenmouth
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