Reed switches are great as long as they are working correctly. But they=20
have a tendency to tack and sometimes intermittently. Sometimes they are=20
just slow to release.
Unless it is difficult to replace a failed switch I would pursue a=20
separate safety scheme. Consider a return line to the main tank from the=20
header tank that will assure a spill proof system. Also,  an alarm on on=20
the pump ( or a shutdown ) in the case of an excessive run time cycle.
I prefer independent safety systems.

On 10/16/2013 9:22 AM, Carl Denk wrote:
> Recently the reed contacts welded together causing a possible unsafe
> condition of overflowing gasoline. I have new switches ordered, the
> question is, is the current configuration of the usual alarm circuit,
> normally powered, and a fault (could be a broken wire) open is detected
> and shuts thing down. But with welded contacts that's bad.:(  It
> wouldn't be hard to make the reed switch NO, change the relay contact
> used to NO, and program the PLC for inverted action to make the circuit
> powered is alarm. Think it's about which is better scenario.

--=20
John Ferrell W8CCW
"Shut her down Scotty, she's sucking mud again!"


--=20
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