In this mode, a device shall be controlled entirely by the Control System. Starting and stopping pumps or closing and opening valves shall be performed automatically and in accordance with the relevant sequence- and control algorithms. The operator shall not have the capability to issue a command individually to a device while it is in the automatic mode. However, the current status of the device shall be monitored and indicated on the display devices of the SCADA system.
In the manual mode, a device shall be operated by issuing commands from the operating console of the SCADA system utilizing dialogue boxes, buttons and other appropriate tools. The level of authorization identified by log-in-code limits the extent of operations. Only operators logged in with sufficient level of authorization shall be allowed to perform particular operations. Safety interlocks associated with such operations shall be activated and executed within the second (PLC) layer of the Control System.
The local mode can be set by activating a hardware switch installed locally to that item (in the field). In this mode, the only possible way to issue a command to that equipment item shall be via a dedicated hardware switch also placed locally to that item. The operator performing actions on equipment in local mode shall have full responsibility for those actions as the safety interlocks implemented within the Control System will be bypassed in this mode.