xgrapher:
I have a sensor that outputs 0~5V and I want to be able to hook up a circuitry onto that signal wire in order to reduce a dynamically defined percentage of the voltage.
Are you saying that the "line voltage" (or estimated voltage of the line with respect to ground) is dependent on the sensor's output voltage (in the range 0 to 5 volt), and you want to be able to adjust the output voltage of the sensor?
When you indicate 'reduce a dynamically defined percentage of the voltage', does this mean you want to alter the sensor's output voltage (which is the voltage of the line)?