transfer analog signal via RJ45 cable
A standard technique to deal with line losses and sensors is to use two pairs of wires for the sensors. One pair is used to carry the excitation or power to the sensor (and you don't care if there are line losses here), whereas a second paid of wires are used ONLY to measure the voltage across the sensor. Since these sense wires carry almost no current (AD converters usually have a high input impedance), there are no negligible line losses and you get a good measurement, even with 100's of metres of wire. Your RJ45 conector/cable has lots of conductors, so maybe you can make this work.

You do need to take care that you don't create a ground loop. The easiest way to do this is to measure the output voltage on the sense pair with a differential AD circuit.