4-20 mA signals from instrument (transmitters) are analog input to control system.

4-20 mA signals to instrument (I/p & electro pneumatic positioner) are analog output from control system.

Volt free (24V) contact (NO/NC) by instruments (all type of switches, ex. Limit switch, press,temp,flow,level switch) are digital input to control system.

All powered signals (24V,48V,110V….) from system to instruments (SOV) are Digital outputs.