SCADA system specification

ANSWER:

• General SCADA Requirements categories might include:
• System availability and failure recovery including redundancy
• Maintainability including a proven support track record for the vendor/system
• Compatibility with existing systems to capitalize on existing infrastructure
• System performance including scan rates, response times, and system loading
• Security, for obvious reasons
• System expandability including the ability to extend all requirements of the system and the use of open communication protocols
• Data retention and management, in support of regulatory requirements such as 21CFR11 Compliance

A specific SCADA sub-section in a URS for a packaged vendor supplied process automation skid that is to be connected to a site SCADA system might read as follows:

1.1.1 Supplier shall exchange data with the site SCADA system in the form of a data map that presents the following data from the site SCADA system:

• All Inputs and Outputs (I/O)
• Alarms
• Interlocks and Permissives
• Recipe Parameters (Pressure Set points, motor speeds etc.), if applicable
• Modes
• Batch Execution Events (Start/Stop/Hold/Restart etc.) if applicable
• Key Process Parameters (such as Min/Max pressures, sample times etc.)
• Batch End Report Parameters if applicable
• Other Events (i.e. operator actions, system events)
• Communications Watchdogs

I suggest that you investigate whether your local ISA chapter sponsors local classes on SCADA as I am aware of local chapters that do provide formal training courses on the subject.

Additional places to look for information:

• GAMP JETT Forum
• IEEE including standard C37.1-1994, "IEEE Standard Definition, Specification, and Analysis of Systems Used for Supervisory Control, Data Acquisition, and Automatic Control"
• Online user discussion archives such as “The SCADA Gospel” 
• White papers, case studies, and specifications can be found from many of the major automation suppliers such as Citect or Emerson Process Management

Scott Clark, Senior Engineer, Automation & Information Services, Merck & Co. Inc.

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