Independent Alarm System


Implement an independent alarm system for an oil and gas refinery using Allen-Bradley ControlLogix PLCs and a CitectSCADA HMI. Provide centrally displayed plant wide alarm monitoring.

  • Four pairs of seven slot redundant Allen-Bradley ControlLogix processors located in four panels in the central control room.
  • Four pairs of ten slot redundant Allen-Bradley ControlLogix racks with up to eight CNET communications modules each.
  • Nine pairs of redundant Allen-Bradley ControlLogix processors in enclosures/panels located in various locations throughout the refinery; designed to allow expansion to a total of thirty two redundant processors.
  • Two pairs of redundant CitectSCADA HMI servers to communicate with equipment PLCs and serve data to clients.
  • Four Microsoft Access databases to store alarm configurations.
  • One Visual Basic application designed as a user interface for entering data into the Access database tables.
  • Thirty CitectSCADA clients designed to mimic annunciator panels.
  • Thirty 50 inch plasma screens, used as monitors for the CitectSCADA clients, mounted above the Honeywell Universal Stations.
  • Integration with Honeywell’s TDC3000 via a Modbus link.
  • One pair of redundant Pepperl & Fuchs Remote Process Interfaces (RPI).
  • Capacity to monitor up to 9,600 field devices.

The Independent Alarm System (IAS) monitors, displays, and annunciates process alarms via multiple display stations. Each display station has 160 cells that communicate over Ethernet with the CitectSCADA servers. The system also communicates the alarms over Modbus to a Honeywell TDC3000 DCS for monitoring the health of the system and logging the alarms. The operator can also bypass alarms from the Honeywell TDC3000, which is written back to the IAS over Modbus.

The system is designed to be fully configurable using a custom Visual Basic program as a user interface to enter data into the Access database tables. The CitectSCADA HMI accesses the database tables via SQL queries and downloads the data to the PLCs, CitectSCADA servers, and CitectSCADA display clients. With the proper security credentials, the operator can add new or modify the existing alarm configurations without modifying the PLC logic or editing the HMI application.

The PLC configuration parameters that can be edited by the operator include, but are not limited to, alarm location, type, priority, and process status. The HMI parameters available for modification via the custom configuration tool include the alarm sound, color, cell border color, and screen location. The operator can also enter ranges and setpoints for analog alarms as well as set the alarm type as high, low, or disabled.

The CitectSCADA HMI application was designed to allow point-to-point online replacement. If the new inputs are the same configuration, the application can replace an input being decommissioned in the PLCs and on the HMI screens with the newly commissioned input within seconds.

Full system documentation and testing were provided including User Requirements Specification, Functional Specification, Software Design Specification, Hardware Design Specification, Factory Acceptance Test, and Site Acceptance Test. Onsite commissioning and support were also provided.


The control system was staged at ACE’s facility in multiple phases and tested prior to shipment to the field. ACE provided assistance with onsite installation and startup of the alarm management system. ACE continues to provide onsite and offsite assistance, including maintenance and services to add additional remote I/O locations as the site expands.