The Pressure Switch (
http://www.andymark.com/product-p/am-2006.htm) reads the air pressure in the system and tells the shuts off the compressor when 120 psi is hit by communicating with the Digital Sidecar. That is why you specify the relay and digital input output port when coding. The relay is for the compressor and the DIO is for the switch that gives a reading and shuts off the compressor when that reading hits 120 psi. I have seen other teams read the psi using that but i wanted to know how we can do it the same way.