An alternate solution to expanding and upgrading a DCS with same vendor parts is to consider a hybrid solution.
Because of cost constraints and limited production downtime, the plant opted for a hybrid solution consisting of replacement of obsolete operator stations by an off-the-shelf HMI and interfacing these into the existing plant architecture.
A graphics converter worked to convert the DCS graphics to the HMI format. Minor modifications to the graphics were required. A standard interface provided by the DCS vendor between the HMI and the DCS network completed the integration.
Another avenue embraces digital automation systems (DAS). Although at one time state-of-the-art, proprietary DCS systems were challenging to maintain and not as reliable, secure, robust, or scalable as standards-based, high speed, digital automation systems.
However, the interoperable nature of a DAS enables it to connect with DCS and PLC systems to:
• Provide scalability
• Incorporate new bus technology
• Improve process optimization
• Lower maintenance costs
• Integrate smart diagnostics
A digital automation system offers multiple migration techniques enabling process manufacturers to choose the best solution for their transition to a digital automation system.
These solutions all ensure minimal downtime and a phased approach to the migration process. Over time, the digital automation system will completely replace the proprietary system.
Cable connection: Controllers in a digital automation system can connect to the existing termination panel of a DCS using a trademarked cable and a mass termination block.
After simply connecting the cables, software running in the digital automation system verifies input/output configurations then either connects directly to the controller or uses OPC to set up communications.
The digital automation system then uses file conversion utilities to translate and replicate DCS graphics and engineering configurations such as batch applications.
In addition, it is easy to build high-resolution graphics in the digital automation system as time permits. Upon completion of these steps, advanced control applications, such as tuning, quickly get the process to optimum capacity.
This solution uses existing wiring and engineering configurations, does not disturb field connections, eliminates engineering configuration, and produces minimal downtime.
Some process manufacturers will use a serial interface and MODBUS protocol to set up communications between the proprietary system and the digital control system.
This solution uses a serial I/O card in the digital automation system controller with a serial communications link. This requires custom written drivers for both ends of the serial link. Some types of proprietary systems will require using this migration method.
Console connection: An OPC server gets data from the proprietary control system, puts the data into a standard format, and reads to an OPC-compliant client.
Normally, a server provides data to clients only; however, a digital automation system enables data sharing between OPC servers.
This functionality not only links to the control system but to all plant subsystems.
This creates plant-wide interoperability at the workstation level.
Source: Fundamentals of Industrial Control, ISA Press, 2005.