The SEC 3500 HMI Operator Interface, an Attendant-Monitored system, continuously interrogates up to 254 system devices over the 9600 baud RS485 Modbus Interface. The OI, operating as the Modbus Master, can communicate with any SEC 3500 Device and any 4-20 transmitter via the SEC 3100 AIM.

There is a power indicator LED located on the front panel of the 3500. Network devices can be interrogated, configured, and calibrated using the password protected touchscreen user interface.