Nascheme,
Just a little more info to add, to set up the speed sensor on an ART-120, you want to press the button for speed mode, then hold the up arrow for 3 seconds to change the speed sensor type. There are several options to choose from, which are outlined below:
OFF - no speed sensor, test speed will be used
GND0 - 1:1 ratio on the monitor minidin port
GND1 - 1:1 ratio on splitter fan port
GND2 - 1:1 ratio on splitter aux1 port
GND3 - 1:1 ratio on splitter aux2 port
RDR0 - 32:1 ratio on the monitor minidin port
RDR1 - 32:1 ratio on splitter fan port
RDR2 - 32:1 ratio on splitter aux1 port
RDR3 - 32:1 ratio on splitter aux2 port