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Per Splatz's original post, the problem was that the inputs were not isolated. Looping the current signal was not an option. OK, leaving one set for current and the other set for voltage might confuse the next guy if he doesn't truly understand analog signals. That said, set them both to voltage and use a common shunt resistor. 250 ohm for 0-5v(1-5v actual) or 500 ohm for 0-10v(2-10v). The inputs when set to voltage will be some very high impedance so paralleling won't be a load issue as they are still significantly higher then the shunt resistor. The transmitter will never know the difference. It will still be controlling current. Per Splatz's comment, the inputs are on the same controller so they are probably not very far apart, so you will only have a voltage signal essentially between them. Hummmm, single, 25 cent component or $75 or more loop splitter? Since this is storm water control, my bet is NASA grade calibration is probably not necessary.
A surge arrestor anytime your transducer is outside is never a bad idea.

Ive done this at home on arduino's but im not sure i would ever do it in the field unless its a patch to get me through the night.

Honestly if a customer is using a engineering firm who sub's the job to a contractor $75 wont cover lunch. Its a dam good idea looking for a problem.
 

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Lift station panels we are working on now have both plc and relay logic controls. If the plc is up then they run off a level sensor with a fancy touch screen and more information then you could possibly use. (mainly used for remote monitoring)
If something happens and it hits the high level float then a latch relay will sound the alarm, start one pump, delay the second pump (in case we are on generator) then run both to low level where it will be unlatched.
 

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Lift station panels we are working on now have both plc and relay logic controls. If the plc is up then they run off a level sensor with a fancy touch screen and more information then you could possibly use. (mainly used for remote monitoring)
If something happens and it hits the high level float then a latch relay will sound the alarm, start one pump, delay the second pump (in case we are on generator) then run both to low level where it will be unlatched.
Done many like that. Had one lift station were the mechanical contractor came in a few months after the project was complete to work on the piping, Dry well side was about 3 stories below ground level. Anyway, he turned off the pumps from the touchscreen only, went down stairs and proceeded to disassemble the 12" piping to work on the check valve. He had the system down for about 3 hours when the backup float got tripped. He then had a 75HP pump blowing raw sewage out the open 12" pipe. He had quite the mess to clean up.
 

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Had a smart relay that flaked out. They had just programmed input to turn on output. Replaced with ice cube relay.
 
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