The monitoring system with LCD´s is already there, also analog to digital converters modules, I don´t have to change anything buying new modules. I´ve been repairing some of these modules, also adapting signals, I´m pretty sure the system installed on board was never working properly because of its configuration... I solved a lot of wrong things at this yacht.
Now, to finish the complete job I have to adapt this sensor signal, in this case 4 to 8 mA to a scale 0,4V to 2V used by the inputs of A/D converter modules. I usually repair and I don´t design a lot so I don´t remember very well when at school we calculated transistor circuits (Ib, Ic, Vce...).
My idea was to use a DC/DC to have a constant voltage, for example 5V, then a transistor circuit where changes the output voltage depending on the input at base (sensor signal), if necessary I can amplify the input with an operational amplifier which would drive the transistor, I can play with variable resistors to get the correct output scale, what do you think?