Keywords: Distributed Control System (DCS), Safety Instrumented System (SIS), Alarm Management, Human Centred Design (HCD), mimics, cybersecurity.
In 2002, the first Distributed Control System (DCS) was installed on the Ince site on the ammonium nitrate prills, effluent treatment and concentrator plants, to replace an obsolete Supervisory Control and Data Acquisition (SCADA) system. Since then, the DCS system has been installed on all plant areas to replace existing ‘Hard’ control systems.
A ‘Hard’ control system / desk can be classified as one which has panels or desks equipped with equipment, such as controllers, chart recorders, gauges, alarms and push buttons. This approach, when designed well, ensured that all indicators, controls etc. were generally laid out to give a complete overview of the process at a glance. All information was typically on display at all times and could easily be viewed by other operators and engineers when required.
It should however be noted that, at Ince, these panels were modified greatly since they were first installed, with different controllers, indicators etc. which degraded their operability from their original design concept. For example, pneumatic and electronic controllers of different vintage and manufacturers were commonplace on a single control panel. New recorders, indicators and controllers were often shoe-horned in to any available space.
The DCS system when first installed could be classed as a ‘Soft control desk – first generation’. This is defined by the fact that when installed, the DCS graphics were designed to emulate the layout and functionality of the replaced panel instruments. Controller faceplates were designed to be familiar with the operators in function, colours used etc. On the prill plant, the controller faceplates look and feel the same as the legacy SCADA faceplates. On the ammonia plant, the controller faceplates were designed to look and feel like our standard programmable single loops controllers.
Whilst this approach greatly aided our operators with familiarisation, it has led to the operation of the plants being performed mainly on fixed controller faceplate displays. With the current design, multiple screens are required to allow the operators to display all the key faceplate screens to give good coverage of all the plants key controllers.
This paper describes how our systems have evolved, and how we are going to design our DCS system operator interfaces going forward, whilst taking human factors into account. Also, briefly discussed is our vision for the future developments of our DCS systems.
Tony Southerton, CF Fertilisers Ltd., Ince, Chester, United Kingdom
24 pages, 13 figures, 3 plates, 1 table, 1 appendix, 3 references