'POT' issues with long cable

[Archangel]

Joe, Copper is fine if it is 'inert' like a length of pipework... but as soon as you start applying any sort of voltage to it (even if it's micro-volts) it causes electrolysis which speeds up it's demise.

I am well aware of electrolysis and DC electricity, as you stated:

The secret is to have AC excitation at the probes... electrolyis is then minimal if not completely eradicated. . .

I'm not talking about the total destruction of your probe into a heap of debris at the bottom of your tank... think about it... if you are measuring Capacitance or Resistance, the smallest change of just the surface of your probe makes massive changes in your measurements rendering the probe useless - that can happen after only a few days of service!!

Yeah . . . that's the principle behind electrolytic capacitors, makes them smaller. Again, isn't this a DC problem? I think HIS solution is dependent upon His situation. Is there DC current IN the solution? Is the DC current on constantly, as in a constant monitoring situation? Or is it a check the level once or twice a day situation? How much money is he willing to spend? I have a motor home which has a galvanized steel water tank which has a wire probe to sense the water level, hooked to an analogue meter. this camper is a 1967 model year, and it still works and is not S.S. . The key is it only works when you push the button. I work with stainless steel on an ongoing basis, in a machine shop, and some of it is truly evil to work with. My argument is, unless this is a Life Critical, or very well paid for project which must last for many many years, then there may be alternatives to the highest priced solution. Then as for copper pipe not having electricity you might not be aware in the US the mains are usually grounded to the water supply. Your tank type water heater has a Magnesium sacrificial anode inside to handle electrolysis.