What are the advantages of a 4 - 20 mA output?

The reasons of the enormous spread of this output type are simple handling and, above all, interference immunity. A current signal has a higher interference immunity than a voltage signal, because electromagnetic interference is fed into the signal line as voltage signals, and causes only very low current changes to the load of the receiver. Due to the 4 mA in the offset range, in addition efficient wire break monitoring can be implemented.