All relevant product information can be found on the Analox Sensor Technology website, take a look at the O2NE+  and Safe-Ox+ product pages. 

The 4-20mA outputs must be requested when ordering as they are a factory fitted option. 

The two-wire (1 positive 1 negative) 4-20mA loop is a continuous (not pulsed) signal.

A simple passive or loop powered monitor can be used with this output.