I've worked with industrial 4-20ma current loops for decades and they can be somewhat tricky to wire up if you haven't worked with them before. First a 250 ohm resistor is the normal resistor used that results in a 1-5vdc measurement range representing a 0-100% of the sensor's measurement range. Second you need to know if the sensor is 'loop powered' or not. If the sensor does not have it's own source of power then it's expecting an external voltage source to power the two wire current loop, normally a 24vdc in the most common loop voltage to use, however sometimes you can go as low as 12vdc if the loop is short. A link to the data sheet should help answer on how the loop needs to be powered wired up.
Lefty