[aprssig] FEMA- Flood gauges (feedback)
ross at topwire.co.nz
Thu Sep 15 16:25:08 CDT 2016
> 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.
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