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.