Independent power supply and loop power supply generally refer to the power supply mode of the module; output looop power supply usually refers to the signal circuit is passive and needs external power supply
Independent powered: The isolated barrier needs independent 24V power supply.
Loop powered: No external power supply is needed. The signal acquisition loop and the power distribution loop share one loop. E.g. GS8531-EX. It should be noted that: (1) The output accuracy of the loop power supply will be lower than that of the independent power supply （2）The formula Uo=Ue-0.02*RL-Ud requires Uo≥ minimum working voltage of the field transmitter.
For example：Assuming that power supply in the safe area, voltage Ue=24V, the load resistance of the field 2-wire transmitter is 300Ω, and the voltage drop of the isolated barrier Ud=6V, then Uo=24-0.02*300-6=12V. If the minimum working voltage of field 2-wire transmitter is 15V, the Uo＜minimum working voltage of the field transmitter. In this case, the following methods could solve this problem:
● Reduce Ud: Select an isolated barrier with a smaller voltage drop;
● Reduce RL: Select a transmitter with smaller load resistance;
● Select a transmitter with a wider working voltage range so that it can work normally at 12V;
● Increase Ue: Increase the power supply voltage of the isolated barrier (the maximum working voltage of the isolated barrier is 35V).
Output loop powered：The output is loop powered. It outputs passive signals, which need DCS/PLC to provide external power supply, such as GS8547-EX（Output loop powered）.