Neil:

Have you had these suicidal impulses for long? :-)

I'm sure you are aware of the huge safety issues. Isolating all
your line voltage switching circuitry from the control circuitry
is not trivial. Relays are good, but there's creepage, leakage,
physical barriers...

Even for the level sensing, it's probably not a good idea to get
your voltages wet. Aside from the safety issues, output from electrodes
in contact with the water/chemical solution may not be stable.
For level sensing, GEMS makes some float-type modules that are very
reliable and inherently isolated.

What does the existing control system use for temperature sensing?
You can probably adapt that same sensor to your new circuit.

Reg Neale

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