Connections diagram
Tomble, ericgibbs and aljamri, thank you for yours repplies.
Aljamri, it was my fault. I wrote it wrong. I should had written "(to get 1-5V from 4-20mA)". Thank you!
Tomble, I think it can be really the problem, so, as ericgibbs asked, I put the connections diagram so we can check it.
ericgibbs, here they are: two_supplies.png and single_supply.png.
I've also realized some strange behavior:
1 - When I use single supply connection, when I measure the Voltage (circuit GND as measuring reference) at the input pin of the ADC, I get always an apparently constant correct value (as it should be after passing through the OPAMP configuration), even when ADC output is fluctuating.
For example: with 4mA from the sensor, 1V is gotten through the 250 Ohm resistor and also at the ADC input pin;
2 - With two power supplies, the 4-20mA sensor power supply of 12-13V, and the current of 4mA through closed loop, I still get 1V over the 250 Ohm resistor, but I get about 1.64V at the ACD input (reference at circuit GND);
3 - When I use a power supply of 24V for the 4-20mA sensor, for 4mA in the closed loop I still get 1V over the 250 Ohm resistor, but now I get about 2.25V over the ACD input (reference at circuit GND).
4 - The values gotten in cases 2 e 3 seems to be constant at the multimeter (voltage meter), by the ADC outputs fluctuates.
I hope it may give us some direction.
If I convert the 4-20mA of the closed loop with another circuit and them use an linear opto between the closed loop circuit and the circuit input, it would help?
Thank you again!!!!!