Differential voltage measurement with Arduino UNO
You do not need to do any kind of differential measurement here. The
Arduino analog input measures voltages relative to ground. Then, as long
as the Arduino and the power supply share a common ground, you should be
fine.

On the other hand, you may need a voltage divider. I have seen a few
sensors interfaced the same way (GND, +24V and signal), which output a
voltage between 0 and +10&nbsp;V. That could fry the Arduin, and maybe
also the sensor. Check the datasheet to see the maximum voltage the
sensor can output, and use a voltage divider to get that safely into the
0 –&nbsp;+5&nbsp;V range.